threads / patch / 63170

v4, 8 partsrefs/files: remove redundant check in split_symref_update()

Subject: [PATCH v4 1/8] refs/files: remove redundant check in split_symref_update()

## tl;dr

19 messages between Mar 20, 2025 and Mar 25, 2025. Diffs are folded; open one to read it.

replies: 18people: 2as markdown or json

Karthik Nayak· Mar 20, 2025, 11:43 UTC · lore

[PATCH v4 0/8] refs: introduce support for batched reference updates

Git supports making reference updates with or without transactions. Updates with transactions are generally better optimized. But transactions are all or nothing. This means, if a user wants to batch updates to take advantage of the optimizations without the hard requirement that all updates must succeed, there is no way currently to do so. Particularly with the reftable backend where batching multiple reference updates is more efficient than performing them sequentially.

This series introduces support for batched reference updates without transactions allowing individual reference updates to fail while letting others proceed. This capability is exposed through git-update-ref's `--allow-partial` flag, which can be used in `--stdin` mode to batch updates and handle failures gracefully. Under the hood, these batched updates still use the transactions infrastructure, while modifying sections to allow partial failures.

The changes are structured to carefully build up this functionality:

First, we clean up and consolidate the reference update checking logic. This includes removing duplicate checks in the files backend and moving refname tracking to the generic layer, which simplifies the codebase and prepares it for the new feature.

We then restructure the reftable backend's transaction preparation code, extracting the update validation logic into a dedicated function. This not only improves code organization but sets the stage for implementing partial transaction support.

To ensure we only skip errors which are user-oriented, we introduce typed errors for transactions with 'enum ref_transaction_error'. We extend the existing errors to include other scenarios and use this new errors throughout the refs code.

With this groundwork in place, we implement the core batch update support in the refs subsystem. This adds the necessary infrastructure to track and report rejected updates while allowing transactions to proceed. All reference backends are modified to support this behavior when enabled.

Finally, we expose this functionality to users through git-update-ref(1)'s `--allow-partial` flag, complete with test coverage and documentation. The flag is specifically limited to `--stdin` mode where batching multiple updates is most relevant.

This enhancement improves Git's flexibility in handling reference updates while maintaining the safety of atomic transactions by default. It's particularly valuable for tools and workflows that need to handle reference update failures gracefully without abandoning the entire batch of updates.

This series is based on top of 683c54c999 (Git 2.49, 2025-03-14) with Patrick's series 'refs: batch refname availability checks' [1] merged in.

[1]: https://lore.kernel.org/all/20250217-pks-update-ref-optimization-v1-0-a2b6d87a24af@pks.im/
---
Changes in v4:
- Rebased on top of 2.49 since there was a long time between the
  previous iteration and we have a new release.
- Changed the naming to say 'batched' updates instead of 'partial
  transactions'. While we still use the transaction infrastructure
  underneath, the new naming causes less ambiguity.
- Clean up some of the commit messages.
- Raise BUG for invalid update index while setting rejections.
- Fix an incorrect early return.
- Link to v3: https://lore.kernel.org/r/20250305-245-partially-atomic-ref-updates-v3-0-0c64e3052354@gmail.com
Changes in v3:
- Changed 'transaction_error' to 'ref_transaction_error' along with the
  error names. Removed 'TRANSACTION_OK' since it can potentially be
  missed instead of simply 'return 0'.
- Rename 'ref_transaction_set_rejected' to
  'ref_transaction_maybe_set_rejected' and move logic around error
  checks to within this function.
- Add a new struct 'ref_transaction_rejections' to track the rejections
  within a transaction. This allows us to only iterate over rejected
  updates.
- Add a new commit to also support partial transactions within the
  batched F/D checks.
- Remove NUL delimited outputs in 'git-update-ref(1)'.
- Remove translations for plumbing outputs.
- Other small cleanups in the commit message and code.
Changes in v2:
- Introduce and use structured errors. This consolidates the errors
  and their handling between the ref backends.
- In the previous version, we skipped over all failures. This include
  system failures such as low memory or IO problems. Let's instead, only
  skip user-oriented failures, such as invalid old OID and so on.
- Change the rejection function name to `ref_transaction_set_rejected()`.
- Modify the commit messages and documentation to be a little more
  verbose.
- Link to v1: https://lore.kernel.org/r/20250207-245-partially-atomic-ref-updates-v1-0-e6a3690ff23a@gmail.com
 Documentation/git-update-ref.adoc |  14 +-
 builtin/fetch.c                   |   2 +-
 builtin/update-ref.c              |  67 ++++-
 refs.c                            | 162 ++++++++++--
 refs.h                            |  76 ++++--
 refs/files-backend.c              | 314 +++++++++++-------------
 refs/packed-backend.c             |  69 +++---
 refs/refs-internal.h              |  51 +++-
 refs/reftable-backend.c           | 502 +++++++++++++++++++-------------------
 t/t1400-update-ref.sh             | 233 ++++++++++++++++++
 10 files changed, 968 insertions(+), 522 deletions(-)
Karthik Nayak (8):
      refs/files: remove redundant check in split_symref_update()
      refs: move duplicate refname update check to generic layer
      refs/files: remove duplicate duplicates check
      refs/reftable: extract code from the transaction preparation
      refs: introduce enum-based transaction error types
      refs: implement batch reference update support
      refs: support rejection in batch updates during F/D checks
      update-ref: add --batch-updates flag for stdin mode
Range-diff versus v3:
1:  c54471c108 ! 1:  0ddde0cb83 refs/files: remove redundant check in split_symref_update()
    @@ Commit message
         The second check is unnecessary because the first one guarantees that
         `string_list_insert()` will never encounter a preexisting entry.
     
    -    Since `item->util` is only used in this context, remove the assignment and
    -    simplify the surrounding code.
    +    The `item->util` field is assigned to validate that a rename doesn't
    +    already exist in the list. The validation is done after the first check.
    +    As this check is removed, clean up the validation and the assignment of
    +    this field in `split_head_update()` and `files_transaction_prepare()`.
     
         Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
     
2:  438ed0b49a ! 2:  4eba9153ff refs: move duplicate refname update check to generic layer
    @@ refs/reftable-backend.c: static int reftable_be_transaction_prepare(struct ref_s
      		}
      
     @@ refs/reftable-backend.c: static int reftable_be_transaction_prepare(struct ref_store *ref_store,
    + 		}
      	}
      
    - 	string_list_sort(&refnames_to_check);
     -	ret = refs_verify_refnames_available(ref_store, &refnames_to_check, &affected_refnames, NULL,
     +	ret = refs_verify_refnames_available(ref_store, &refnames_to_check,
     +					     &transaction->refnames, NULL,
3:  acdaa636d9 = 3:  a06733298d refs/files: remove duplicate duplicates check
4:  fc61deb9c6 ! 4:  707afdb039 refs/reftable: extract code from the transaction preparation
    @@ Commit message
         The refactoring consolidates all reference update validation into a
         single logical block, which improves code maintainability and
         readability. More importantly, this restructuring lays the groundwork
    -    for implementing partial transaction support in the reftable backend,
    -    which will be introduced in the following commit.
    +    for implementing batched reference update support in the reftable
    +    backend, which will be introduced in a followup commit.
     
         No functional changes are included in this commit - it is purely a code
         reorganization to support future enhancements.
    @@ refs/reftable-backend.c: static int reftable_be_transaction_prepare(struct ref_s
     -		}
      	}
      
    - 	string_list_sort(&refnames_to_check);
    + 	ret = refs_verify_refnames_available(ref_store, &refnames_to_check,
5:  c494ff7e99 ! 5:  b93c3f3f9f refs: introduce enum-based transaction error types
    @@ Commit message
             common scenarios.
     
         This refactoring paves the way for more comprehensive error handling
    -    which we will utilize in the upcoming commits to add partial transaction
    -    support.
    +    which we will utilize in the upcoming commits to add batch reference
    +    update support.
     
         Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
     
    @@ refs.c: int ref_transaction_commit(struct ref_transaction *transaction,
      {
      	struct strbuf dirname = STRBUF_INIT;
      	struct strbuf referent = STRBUF_INIT;
    + 	struct string_list_item *item;
      	struct ref_iterator *iter = NULL;
      	struct strset dirnames;
     -	int ret = -1;
    @@ refs/packed-backend.c: static int write_with_updates(struct packed_ref_store *re
      					    "reference is missing but expected %s",
      					    update->refname,
      					    oid_to_hex(&update->old_oid));
    -+				return REF_TRANSACTION_ERROR_NONEXISTENT_REF;
    ++				ret = REF_TRANSACTION_ERROR_NONEXISTENT_REF;
      				goto error;
      			}
      		}
6:  b051e51162 ! 6:  feacd50666 refs: implement partial reference transaction support
    @@ Metadata
     Author: Karthik Nayak <karthik.188@gmail.com>
     
      ## Commit message ##
    -    refs: implement partial reference transaction support
    +    refs: implement batch reference update support
     
    -    Git's reference transactions are all-or-nothing: either all updates
    -    succeed, or none do. While this atomic behavior is generally desirable,
    -    it can be suboptimal especially when using the reftable backend, where
    -    batching multiple reference updates into a single transaction is more
    -    efficient than performing them sequentially.
    +    Git supports making reference updates with or without transactions.
    +    Updates with transactions are generally better optimized. But
    +    transactions are all or nothing. This means, if a user wants to batch
    +    updates to take advantage of the optimizations without the hard
    +    requirement that all updates must succeed, there is no way currently to
    +    do so. Particularly with the reftable backend where batching multiple
    +    reference updates is more efficient than performing them sequentially.
     
    -    Introduce partial transaction support with a new flag,
    -    'REF_TRANSACTION_ALLOW_PARTIAL'. When enabled, this flag allows
    -    individual reference updates that would typically cause the entire
    -    transaction to fail due to non-system-related errors to be marked as
    -    rejected while permitting other updates to proceed. System errors
    -    referred by 'REF_TRANSACTION_ERROR_GENERIC' continue to result in the
    -    entire transaction failing. This approach enhances flexibility while
    -    preserving transactional integrity where necessary.
    +    Introduce batched update support with a new flag,
    +    'REF_TRANSACTION_ALLOW_FAILURE'. Batched updates while different from
    +    transactions, use the transaction infrastructure under the hood. When
    +    enabled, this flag allows individual reference updates that would
    +    typically cause the entire transaction to fail due to non-system-related
    +    errors to be marked as rejected while permitting other updates to
    +    proceed. System errors referred by 'REF_TRANSACTION_ERROR_GENERIC'
    +    continue to result in the entire transaction failing. This approach
    +    enhances flexibility while preserving transactional integrity where
    +    necessary.
     
         The implementation introduces several key components:
     
    @@ Commit message
           - Modify reference backends (files, packed, reftable) to handle
             partial transactions by using `ref_transaction_set_rejected()`
             instead of failing the entire transaction when
    -        `REF_TRANSACTION_ALLOW_PARTIAL` is set.
    +        `REF_TRANSACTION_ALLOW_FAILURE` is set.
     
           - Add `ref_transaction_for_each_rejected_update()` to let callers
             examine which updates were rejected and why.
     
    -    This foundational change enables partial transaction support throughout
    -    the reference subsystem. A following commit will expose this capability
    -    to users by adding a `--allow-partial` flag to 'git-update-ref(1)',
    +    This foundational change enables batched update support throughout the
    +    reference subsystem. A following commit will expose this capability to
    +    users by adding a `--batch-updates` flag to 'git-update-ref(1)',
         providing both a user-facing feature and a testable implementation.
     
         Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
    @@ refs.c: struct ref_transaction *ref_store_transaction_begin(struct ref_store *re
      	tr->flags = flags;
      	string_list_init_dup(&tr->refnames);
     +
    -+	if (flags & REF_TRANSACTION_ALLOW_PARTIAL)
    ++	if (flags & REF_TRANSACTION_ALLOW_FAILURE)
     +		CALLOC_ARRAY(tr->rejections, 1);
     +
      	return tr;
    @@ refs.c: void ref_transaction_free(struct ref_transaction *transaction)
     +	if (update_idx >= transaction->nr)
     +		BUG("trying to set rejection on invalid update index");
     +
    -+	if (!(transaction->flags & REF_TRANSACTION_ALLOW_PARTIAL))
    ++	if (!(transaction->flags & REF_TRANSACTION_ALLOW_FAILURE))
     +		return 0;
     +
     +	if (!transaction->rejections)
    -+		BUG("transaction not inititalized with partial support");
    ++		BUG("transaction not inititalized with failure support");
     +
     +	/*
     +	 * Don't accept generic errors, since these errors are not user
    @@ refs.h: enum ref_transaction_flag {
     +	 * is detected. This flag allows transactions to partially apply updates
     +	 * while rejecting updates which do not match the expected state.
     +	 */
    -+	REF_TRANSACTION_ALLOW_PARTIAL = (1 << 1),
    ++	REF_TRANSACTION_ALLOW_FAILURE = (1 << 1),
      };
      
      /*
    @@ refs/packed-backend.c: static enum ref_transaction_error write_with_updates(stru
     @@ refs/packed-backend.c: static enum ref_transaction_error write_with_updates(struct packed_ref_store *re
      					    update->refname,
      					    oid_to_hex(&update->old_oid));
    - 				return REF_TRANSACTION_ERROR_NONEXISTENT_REF;
    + 				ret = REF_TRANSACTION_ERROR_NONEXISTENT_REF;
     +
     +				if (ref_transaction_maybe_set_rejected(transaction, i, ret)) {
     +					strbuf_setlen(err, 0);
    @@ refs/refs-internal.h: struct ref_update {
      	uint64_t index;
      
     +	/*
    -+	 * Used in partial transactions to mark if a given update was rejected.
    ++	 * Used in batched reference updates to mark if a given update
    ++	 * was rejected.
     +	 */
     +	enum ref_transaction_error rejection_err;
     +
    @@ refs/refs-internal.h: enum ref_transaction_state {
      };
      
     +/*
    -+ * Data structure to hold indices of updates which were rejected, when
    -+ * partial transactions where enabled. While the updates themselves hold
    -+ * the rejection error, this structure allows a transaction to iterate
    -+ * only over the rejected updates.
    ++ * Data structure to hold indices of updates which were rejected, for batched
    ++ * reference updates. While the updates themselves hold the rejection error,
    ++ * this structure allows a transaction to iterate only over the rejected
    ++ * updates.
     + */
     +struct ref_transaction_rejections {
     +	size_t *update_indices;
    @@ refs/reftable-backend.c: static int reftable_be_transaction_prepare(struct ref_s
     +		}
      	}
      
    - 	string_list_sort(&refnames_to_check);
    + 	ret = refs_verify_refnames_available(ref_store, &refnames_to_check,
     @@ refs/reftable-backend.c: static int write_transaction_table(struct reftable_writer *writer, void *cb_data
      		struct reftable_transaction_update *tx_update = &arg->updates[i];
      		struct ref_update *u = tx_update->update;
7:  47d7a64cb4 ! 7:  f20877267d refs: support partial update rejections during F/D checks
    @@ Metadata
     Author: Karthik Nayak <karthik.188@gmail.com>
     
      ## Commit message ##
    -    refs: support partial update rejections during F/D checks
    +    refs: support rejection in batch updates during F/D checks
     
         The `refs_verify_refnames_available()` is used to batch check refnames
         for F/D conflicts. While this is the more performant alternative than
         its individual version, it does not provide rejection capabilities on a
    -    single update level. For partial transactions, this would mean a
    -    rejection of the entire transaction whenever one reference has a F/D
    -    conflict.
    +    single update level. For batched updates, this would mean a rejection of
    +    the entire transaction whenever one reference has a F/D conflict.
     
         Modify the function to call `ref_transaction_maybe_set_rejected()` to
         check if a single update can be rejected. Since this function is only
    @@ refs.c: enum ref_transaction_error refs_verify_refnames_available(struct ref_sto
     @@ refs.c: enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs
      	strset_init(&dirnames);
      
    - 	for (size_t i = 0; i < refnames->nr; i++) {
    -+		const size_t *update_idx = (size_t *)refnames->items[i].util;
    - 		const char *refname = refnames->items[i].string;
    + 	for_each_string_list_item(item, refnames) {
    ++		const size_t *update_idx = (size_t *)item->util;
    + 		const char *refname = item->string;
      		const char *extra_refname;
      		struct object_id oid;
     @@ refs.c: enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs
    @@ refs/files-backend.c: static enum ref_transaction_error lock_raw_ref(struct file
      		 * make sure there is no existing packed ref that conflicts
      		 * with refname. This check is deferred so that we can batch it.
      		 */
    --		string_list_insert(refnames_to_check, refname);
    -+		item = string_list_insert(refnames_to_check, refname);
    +-		string_list_append(refnames_to_check, refname);
    ++		item = string_list_append(refnames_to_check, refname);
     +		item->util = xmalloc(sizeof(update_idx));
     +		memcpy(item->util, &update_idx, sizeof(update_idx));
      	}
    @@ refs/refs-internal.h: enum ref_transaction_error ref_update_check_old_target(con
     + * refnames instead of only a single item. This is more efficient in the case
     + * where one needs to check multiple refnames.
     + *
    -+ * If a transaction is provided with partial support, then individual updates
    -+ * are marked rejected, reference backends are then in charge of not committing
    -+ * those updates.
    ++ * If using batched updates, then individual updates are marked rejected,
    ++ * reference backends are then in charge of not committing those updates.
     + */
     +enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs,
     +					  const struct string_list *refnames,
    @@ refs/reftable-backend.c: static int reftable_be_transaction_prepare(struct ref_s
      					    &head_referent, &referent, err);
      		if (ret) {
     @@ refs/reftable-backend.c: static int reftable_be_transaction_prepare(struct ref_store *ref_store,
    - 	string_list_sort(&refnames_to_check);
    + 
      	ret = refs_verify_refnames_available(ref_store, &refnames_to_check,
      					     &transaction->refnames, NULL,
     +					     transaction,
8:  2237086c65 ! 8:  d6f43d5dce update-ref: add --allow-partial flag for stdin mode
    @@ Metadata
     Author: Karthik Nayak <karthik.188@gmail.com>
     
      ## Commit message ##
    -    update-ref: add --allow-partial flag for stdin mode
    +    update-ref: add --batch-updates flag for stdin mode
     
         When updating multiple references through stdin, Git's update-ref
         command normally aborts the entire transaction if any single update
    -    fails. While this atomic behavior prevents partial updates by default,
    -    there are cases where applying successful updates while reporting
    -    failures is desirable.
    +    fails. This atomic behavior prevents partial updates. Introduce a new
    +    batch update system, where the updates the performed together similar
    +    but individual updates are allowed to fail.
     
    -    Add a new `--allow-partial` flag that allows the transaction to continue
    +    Add a new `--batch-updates` flag that allows the transaction to continue
         even when individual reference updates fail. This flag can only be used
    -    in `--stdin` mode and builds upon the partial transaction support added
    -    to the refs subsystem. When enabled, failed updates are reported in the
    -    following format:
    +    in `--stdin` mode and builds upon the batch update support added to the
    +    refs subsystem in the previous commits. When enabled, failed updates are
    +    reported in the following format:
     
           rejected SP (<old-oid> | <old-target>) SP (<new-oid> | <new-target>) SP <rejection-reason> LF
     
    @@ Documentation/git-update-ref.adoc: git-update-ref - Update the object name store
     +[synopsis]
     +git update-ref [-m <reason>] [--no-deref] -d <ref> [<old-oid>]
     +	       [-m <reason>] [--no-deref] [--create-reflog] <ref> <new-oid> [<old-oid>]
    -+               [-m <reason>] [--no-deref] --stdin [-z] [--allow-partial]
    ++               [-m <reason>] [--no-deref] --stdin [-z] [--batch-updates]
      
      DESCRIPTION
      -----------
    @@ Documentation/git-update-ref.adoc: performs all modifications together.  Specify
      With `--create-reflog`, update-ref will create a reflog for each ref
      even if one would not ordinarily be created.
      
    -+With `--allow-partial`, update-ref continues executing the transaction even if
    -+some updates fail due to invalid or incorrect user input, applying only the
    -+successful updates. Errors resulting from user-provided input are treated as
    -+non-system-related and do not cause the entire transaction to be aborted.
    -+However, system-related errors—such as I/O failures or memory issues—will still
    -+result in a full failure. Additionally, errors like F/D conflicts are batched
    -+for performance optimization and will also cause a full failure. Any failed
    ++With `--batch-updates`, update-ref executes the updates in a batch but allows
    ++individual updates to fail due to invalid or incorrect user input, applying only
    ++the successful updates. However, system-related errors—such as I/O failures or
    ++memory issues—will result in a full failure of all batched updates. Any failed
     +updates will be reported in the following format:
     +
     +	rejected SP (<old-oid> | <old-target>) SP (<new-oid> | <new-target>) SP <rejection-reason> LF
    @@ builtin/update-ref.c
      	N_("git update-ref [<options>] -d <refname> [<old-oid>]"),
      	N_("git update-ref [<options>]    <refname> <new-oid> [<old-oid>]"),
     -	N_("git update-ref [<options>] --stdin [-z]"),
    -+	N_("git update-ref [<options>] --stdin [-z] [--allow-partial]"),
    ++	N_("git update-ref [<options>] --stdin [-z] [--batch-updates]"),
      	NULL
      };
      
    @@ builtin/update-ref.c: int cmd_update_ref(int argc,
      		OPT_BOOL('z', NULL, &end_null, N_("stdin has NUL-terminated arguments")),
      		OPT_BOOL( 0 , "stdin", &read_stdin, N_("read updates from stdin")),
      		OPT_BOOL( 0 , "create-reflog", &create_reflog, N_("create a reflog")),
    -+		OPT_BIT('0', "allow-partial", &flags, N_("allow partial transactions"),
    -+			REF_TRANSACTION_ALLOW_PARTIAL),
    ++		OPT_BIT('0', "batch-updates", &flags, N_("batch reference updates"),
    ++			REF_TRANSACTION_ALLOW_FAILURE),
      		OPT_END(),
      	};
      
    @@ builtin/update-ref.c: int cmd_update_ref(int argc,
     +		update_refs_stdin(flags);
      		return 0;
     -	}
    -+	} else if (flags & REF_TRANSACTION_ALLOW_PARTIAL)
    -+		die("--allow-partial can only be used with --stdin");
    ++	} else if (flags & REF_TRANSACTION_ALLOW_FAILURE)
    ++		die("--batch-updates can only be used with --stdin");
      
      	if (end_null)
      		usage_with_options(git_update_ref_usage, options);
    @@ t/t1400-update-ref.sh: do
      		grep "$(git rev-parse $a) $(git rev-parse $a)" actual
      	'
      
    -+	test_expect_success "stdin $type allow-partial" '
    ++	test_expect_success "stdin $type batch-updates" '
     +		git init repo &&
     +		test_when_finished "rm -fr repo" &&
     +		(
    @@ t/t1400-update-ref.sh: do
     +
     +			format_command $type "update refs/heads/ref1" "$head" "$Z" >stdin &&
     +			format_command $type "update refs/heads/ref2" "$head" "$Z" >>stdin &&
    -+			git update-ref $type --stdin --allow-partial <stdin &&
    ++			git update-ref $type --stdin --batch-updates <stdin &&
     +			echo $head >expect &&
     +			git rev-parse refs/heads/ref1 >actual &&
     +			test_cmp expect actual &&
    @@ t/t1400-update-ref.sh: do
     +		)
     +	'
     +
    -+	test_expect_success "stdin $type allow-partial with invalid new_oid" '
    ++	test_expect_success "stdin $type batch-updates with invalid new_oid" '
     +		git init repo &&
     +		test_when_finished "rm -fr repo" &&
     +		(
    @@ t/t1400-update-ref.sh: do
     +
     +			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
     +			format_command $type "update refs/heads/ref2" "$(test_oid 001)" "$head" >>stdin &&
    -+			git update-ref $type --stdin --allow-partial <stdin >stdout &&
    ++			git update-ref $type --stdin --batch-updates <stdin >stdout &&
     +			echo $old_head >expect &&
     +			git rev-parse refs/heads/ref1 >actual &&
     +			test_cmp expect actual &&
    @@ t/t1400-update-ref.sh: do
     +		)
     +	'
     +
    -+	test_expect_success "stdin $type allow-partial with non-commit new_oid" '
    ++	test_expect_success "stdin $type batch-updates with non-commit new_oid" '
     +		git init repo &&
     +		test_when_finished "rm -fr repo" &&
     +		(
    @@ t/t1400-update-ref.sh: do
     +
     +			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
     +			format_command $type "update refs/heads/ref2" "$head_tree" "$head" >>stdin &&
    -+			git update-ref $type --stdin --allow-partial <stdin >stdout &&
    ++			git update-ref $type --stdin --batch-updates <stdin >stdout &&
     +			echo $old_head >expect &&
     +			git rev-parse refs/heads/ref1 >actual &&
     +			test_cmp expect actual &&
    @@ t/t1400-update-ref.sh: do
     +		)
     +	'
     +
    -+	test_expect_success "stdin $type allow-partial with non-existent ref" '
    ++	test_expect_success "stdin $type batch-updates with non-existent ref" '
     +		git init repo &&
     +		test_when_finished "rm -fr repo" &&
     +		(
    @@ t/t1400-update-ref.sh: do
     +
     +			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
     +			format_command $type "update refs/heads/ref2" "$old_head" "$head" >>stdin &&
    -+			git update-ref $type --stdin --allow-partial <stdin >stdout &&
    ++			git update-ref $type --stdin --batch-updates <stdin >stdout &&
     +			echo $old_head >expect &&
     +			git rev-parse refs/heads/ref1 >actual &&
     +			test_cmp expect actual &&
    @@ t/t1400-update-ref.sh: do
     +		)
     +	'
     +
    -+	test_expect_success "stdin $type allow-partial with dangling symref" '
    ++	test_expect_success "stdin $type batch-updates with dangling symref" '
     +		git init repo &&
     +		test_when_finished "rm -fr repo" &&
     +		(
    @@ t/t1400-update-ref.sh: do
     +
     +			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
     +			format_command $type "update refs/heads/ref2" "$old_head" "$head" >>stdin &&
    -+			git update-ref $type --no-deref --stdin --allow-partial <stdin >stdout &&
    ++			git update-ref $type --no-deref --stdin --batch-updates <stdin >stdout &&
     +			echo $old_head >expect &&
     +			git rev-parse refs/heads/ref1 >actual &&
     +			test_cmp expect actual &&
    @@ t/t1400-update-ref.sh: do
     +		)
     +	'
     +
    -+	test_expect_success "stdin $type allow-partial with regular ref as symref" '
    ++	test_expect_success "stdin $type batch-updates with regular ref as symref" '
     +		git init repo &&
     +		test_when_finished "rm -fr repo" &&
     +		(
    @@ t/t1400-update-ref.sh: do
     +
     +			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
     +			format_command $type "symref-update refs/heads/ref2" "$old_head" "ref" "refs/heads/nonexistent" >>stdin &&
    -+			git update-ref $type --no-deref --stdin --allow-partial <stdin >stdout &&
    ++			git update-ref $type --no-deref --stdin --batch-updates <stdin >stdout &&
     +			echo $old_head >expect &&
     +			git rev-parse refs/heads/ref1 >actual &&
     +			test_cmp expect actual &&
    @@ t/t1400-update-ref.sh: do
     +		)
     +	'
     +
    -+	test_expect_success "stdin $type allow-partial with invalid old_oid" '
    ++	test_expect_success "stdin $type batch-updates with invalid old_oid" '
     +		git init repo &&
     +		test_when_finished "rm -fr repo" &&
     +		(
    @@ t/t1400-update-ref.sh: do
     +
     +			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
     +			format_command $type "update refs/heads/ref2" "$old_head" "$Z" >>stdin &&
    -+			git update-ref $type --stdin --allow-partial <stdin >stdout &&
    ++			git update-ref $type --stdin --batch-updates <stdin >stdout &&
     +			echo $old_head >expect &&
     +			git rev-parse refs/heads/ref1 >actual &&
     +			test_cmp expect actual &&
    @@ t/t1400-update-ref.sh: do
     +		)
     +	'
     +
    -+	test_expect_success "stdin $type allow-partial with incorrect old oid" '
    ++	test_expect_success "stdin $type batch-updates with incorrect old oid" '
     +		git init repo &&
     +		test_when_finished "rm -fr repo" &&
     +		(
    @@ t/t1400-update-ref.sh: do
     +
     +			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
     +			format_command $type "update refs/heads/ref2" "$head" "$old_head" >>stdin &&
    -+			git update-ref $type --stdin --allow-partial <stdin >stdout &&
    ++			git update-ref $type --stdin --batch-updates <stdin >stdout &&
     +			echo $old_head >expect &&
     +			git rev-parse refs/heads/ref1 >actual &&
     +			test_cmp expect actual &&
    @@ t/t1400-update-ref.sh: do
     +		)
     +	'
     +
    -+	test_expect_success "stdin $type allow-partial refname conflict" '
    ++	test_expect_success "stdin $type batch-updates refname conflict" '
     +		git init repo &&
     +		test_when_finished "rm -fr repo" &&
     +		(
    @@ t/t1400-update-ref.sh: do
     +
     +			format_command $type "update refs/heads/ref/foo" "$old_head" "$head" >stdin &&
     +			format_command $type "update refs/heads/ref" "$old_head" "" >>stdin &&
    -+			git update-ref $type --stdin --allow-partial <stdin >stdout &&
    ++			git update-ref $type --stdin --batch-updates <stdin >stdout &&
     +			echo $old_head >expect &&
     +			git rev-parse refs/heads/ref/foo >actual &&
     +			test_cmp expect actual &&
    @@ t/t1400-update-ref.sh: do
     +		)
     +	'
     +
    -+	test_expect_success "stdin $type allow-partial refname conflict new ref" '
    ++	test_expect_success "stdin $type batch-updates refname conflict new ref" '
     +		git init repo &&
     +		test_when_finished "rm -fr repo" &&
     +		(
    @@ t/t1400-update-ref.sh: do
     +
     +			format_command $type "update refs/heads/foo" "$old_head" "" >stdin &&
     +			format_command $type "update refs/heads/ref" "$old_head" "" >>stdin &&
    -+			git update-ref $type --stdin --allow-partial <stdin >stdout &&
    ++			git update-ref $type --stdin --batch-updates <stdin >stdout &&
     +			echo $old_head >expect &&
     +			git rev-parse refs/heads/foo >actual &&
     +			test_cmp expect actual &&

base-commit: 679c868f5fffadd1f7e8e49d4d87d745ee36ffb7 change-id: 20241206-245-partially-atomic-ref-updates-9fe8b080345c

Thanks
- Karthik
Karthik Nayak· Mar 20, 2025, 11:43 UTC · re: Karthik Nayak · lore

In `split_symref_update()`, there were two checks for duplicate refnames:

  - At the start, `string_list_has_string()` ensures the refname is not
    already in `affected_refnames`, preventing duplicates from being
    added.
  - After adding the refname, another check verifies whether the newly
    inserted item has a `util` value.

The second check is unnecessary because the first one guarantees that `string_list_insert()` will never encounter a preexisting entry.

The `item->util` field is assigned to validate that a rename doesn't already exist in the list. The validation is done after the first check. As this check is removed, clean up the validation and the assignment of this field in `split_head_update()` and `files_transaction_prepare()`.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 refs/files-backend.c | 20 +++-----------------
 1 file changed, 3 insertions(+), 17 deletions(-)
Show changes to refs/files-backend.c +3 −17
diff --git a/refs/files-backend.c b/refs/files-backend.c
index ff54a4bb7e..15559a09c5 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -2382,7 +2382,6 @@ static int split_head_update(struct ref_update *update,
 			     struct string_list *affected_refnames,
 			     struct strbuf *err)
 {
-	struct string_list_item *item;
 	struct ref_update *new_update;
 
 	if ((update->flags & REF_LOG_ONLY) ||
@@ -2421,8 +2420,7 @@ static int split_head_update(struct ref_update *update,
 	 */
 	if (strcmp(new_update->refname, "HEAD"))
 		BUG("%s unexpectedly not 'HEAD'", new_update->refname);
-	item = string_list_insert(affected_refnames, new_update->refname);
-	item->util = new_update;
+	string_list_insert(affected_refnames, new_update->refname);
 
 	return 0;
 }
@@ -2441,7 +2439,6 @@ static int split_symref_update(struct ref_update *update,
 			       struct string_list *affected_refnames,
 			       struct strbuf *err)
 {
-	struct string_list_item *item;
 	struct ref_update *new_update;
 	unsigned int new_flags;
 
@@ -2496,11 +2493,7 @@ static int split_symref_update(struct ref_update *update,
 	 * be valid as long as affected_refnames is in use, and NOT
 	 * referent, which might soon be freed by our caller.
 	 */
-	item = string_list_insert(affected_refnames, new_update->refname);
-	if (item->util)
-		BUG("%s unexpectedly found in affected_refnames",
-		    new_update->refname);
-	item->util = new_update;
+	string_list_insert(affected_refnames, new_update->refname);
 
 	return 0;
 }
@@ -2834,7 +2827,6 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 	 */
 	for (i = 0; i < transaction->nr; i++) {
 		struct ref_update *update = transaction->updates[i];
-		struct string_list_item *item;
 
 		if ((update->flags & REF_IS_PRUNING) &&
 		    !(update->flags & REF_NO_DEREF))
@@ -2843,13 +2835,7 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 		if (update->flags & REF_LOG_ONLY)
 			continue;
 
-		item = string_list_append(&affected_refnames, update->refname);
-		/*
-		 * We store a pointer to update in item->util, but at
-		 * the moment we never use the value of this field
-		 * except to check whether it is non-NULL.
-		 */
-		item->util = update;
+		string_list_append(&affected_refnames, update->refname);
 	}
 	string_list_sort(&affected_refnames);
 	if (ref_update_reject_duplicates(&affected_refnames, err)) {
-- 
2.48.1
Karthik Nayak· Mar 20, 2025, 11:43 UTC · re: Karthik Nayak · lore

[PATCH v4 2/8] refs: move duplicate refname update check to generic layer

Move the tracking of refnames in `affected_refnames` from individual backends into the generic layer in 'refs.c'. This centralizes the duplicate refname detection that was previously handled separately by each backend.

Make some changes to accommodate this move:
  - Add a `string_list` field `refnames` to `ref_transaction` to contain
    all the references in a transaction. This field is updated whenever
    a new update is added via `ref_transaction_add_update`, so manual
    additions in reference backends are dropped.
  - Modify the backends to use this field internally as needed. The
    backends need to check if an update for refname already exists when
    splitting symrefs or adding an update for 'HEAD'.
  - In the reftable backend, within `reftable_be_transaction_prepare()`,
    move the `string_list_has_string()` check above
    `ref_transaction_add_update()`. Since `ref_transaction_add_update()`
    automatically adds the refname to `transaction->refnames`,
    performing the check after will always return true, so we perform
    the check before adding the update.

This helps reduce duplication of functionality between the backends and makes it easier to make changes in a more centralized manner.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 refs.c                  | 17 +++++++++++++
 refs/files-backend.c    | 67 +++++++++++--------------------------------------
 refs/packed-backend.c   | 25 +-----------------
 refs/refs-internal.h    |  2 ++
 refs/reftable-backend.c | 54 +++++++++++++--------------------------
 5 files changed, 51 insertions(+), 114 deletions(-)
Show changes to 5 files +51 −114

refs.c, refs/files-backend.c, refs/packed-backend.c, refs/refs-internal.h, refs/reftable-backend.c

diff --git a/refs.c b/refs.c
index 2ac9d8ebd0..504bf2063e 100644
--- a/refs.c
+++ b/refs.c
@@ -1175,6 +1175,7 @@ struct ref_transaction *ref_store_transaction_begin(struct ref_store *refs,
 	CALLOC_ARRAY(tr, 1);
 	tr->ref_store = refs;
 	tr->flags = flags;
+	string_list_init_dup(&tr->refnames);
 	return tr;
 }
 
@@ -1205,6 +1206,7 @@ void ref_transaction_free(struct ref_transaction *transaction)
 		free((char *)transaction->updates[i]->old_target);
 		free(transaction->updates[i]);
 	}
+	string_list_clear(&transaction->refnames, 0);
 	free(transaction->updates);
 	free(transaction);
 }
@@ -1218,6 +1220,7 @@ struct ref_update *ref_transaction_add_update(
 		const char *committer_info,
 		const char *msg)
 {
+	struct string_list_item *item;
 	struct ref_update *update;
 
 	if (transaction->state != REF_TRANSACTION_OPEN)
@@ -1245,6 +1248,16 @@ struct ref_update *ref_transaction_add_update(
 		update->msg = normalize_reflog_message(msg);
 	}
 
+	/*
+	 * This list is generally used by the backends to avoid duplicates.
+	 * But we do support multiple log updates for a given refname within
+	 * a single transaction.
+	 */
+	if (!(update->flags & REF_LOG_ONLY)) {
+		item = string_list_append(&transaction->refnames, refname);
+		item->util = update;
+	}
+
 	return update;
 }
 
@@ -2405,6 +2418,10 @@ int ref_transaction_prepare(struct ref_transaction *transaction,
 		return -1;
 	}
 
+	string_list_sort(&transaction->refnames);
+	if (ref_update_reject_duplicates(&transaction->refnames, err))
+		return TRANSACTION_GENERIC_ERROR;
+
 	ret = refs->be->transaction_prepare(refs, transaction, err);
 	if (ret)
 		return ret;
diff --git a/refs/files-backend.c b/refs/files-backend.c
index 15559a09c5..58f62ea8a3 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -2378,9 +2378,7 @@ static struct ref_iterator *files_reflog_iterator_begin(struct ref_store *ref_st
  */
 static int split_head_update(struct ref_update *update,
 			     struct ref_transaction *transaction,
-			     const char *head_ref,
-			     struct string_list *affected_refnames,
-			     struct strbuf *err)
+			     const char *head_ref, struct strbuf *err)
 {
 	struct ref_update *new_update;
 
@@ -2398,7 +2396,7 @@ static int split_head_update(struct ref_update *update,
 	 * transaction. This check is O(lg N) in the transaction
 	 * size, but it happens at most once per transaction.
 	 */
-	if (string_list_has_string(affected_refnames, "HEAD")) {
+	if (string_list_has_string(&transaction->refnames, "HEAD")) {
 		/* An entry already existed */
 		strbuf_addf(err,
 			    "multiple updates for 'HEAD' (including one "
@@ -2420,7 +2418,6 @@ static int split_head_update(struct ref_update *update,
 	 */
 	if (strcmp(new_update->refname, "HEAD"))
 		BUG("%s unexpectedly not 'HEAD'", new_update->refname);
-	string_list_insert(affected_refnames, new_update->refname);
 
 	return 0;
 }
@@ -2436,7 +2433,6 @@ static int split_head_update(struct ref_update *update,
 static int split_symref_update(struct ref_update *update,
 			       const char *referent,
 			       struct ref_transaction *transaction,
-			       struct string_list *affected_refnames,
 			       struct strbuf *err)
 {
 	struct ref_update *new_update;
@@ -2448,7 +2444,7 @@ static int split_symref_update(struct ref_update *update,
 	 * size, but it happens at most once per symref in a
 	 * transaction.
 	 */
-	if (string_list_has_string(affected_refnames, referent)) {
+	if (string_list_has_string(&transaction->refnames, referent)) {
 		/* An entry already exists */
 		strbuf_addf(err,
 			    "multiple updates for '%s' (including one "
@@ -2486,15 +2482,6 @@ static int split_symref_update(struct ref_update *update,
 	update->flags |= REF_LOG_ONLY | REF_NO_DEREF;
 	update->flags &= ~REF_HAVE_OLD;
 
-	/*
-	 * Add the referent. This insertion is O(N) in the transaction
-	 * size, but it happens at most once per symref in a
-	 * transaction. Make sure to add new_update->refname, which will
-	 * be valid as long as affected_refnames is in use, and NOT
-	 * referent, which might soon be freed by our caller.
-	 */
-	string_list_insert(affected_refnames, new_update->refname);
-
 	return 0;
 }
 
@@ -2558,7 +2545,6 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 			       struct ref_transaction *transaction,
 			       const char *head_ref,
 			       struct string_list *refnames_to_check,
-			       struct string_list *affected_refnames,
 			       struct strbuf *err)
 {
 	struct strbuf referent = STRBUF_INIT;
@@ -2575,8 +2561,7 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 		update->flags |= REF_DELETING;
 
 	if (head_ref) {
-		ret = split_head_update(update, transaction, head_ref,
-					affected_refnames, err);
+		ret = split_head_update(update, transaction, head_ref, err);
 		if (ret)
 			goto out;
 	}
@@ -2586,9 +2571,8 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 		lock->count++;
 	} else {
 		ret = lock_raw_ref(refs, update->refname, mustexist,
-				   refnames_to_check, affected_refnames,
-				   &lock, &referent,
-				   &update->type, err);
+				   refnames_to_check, &transaction->refnames,
+				   &lock, &referent, &update->type, err);
 		if (ret) {
 			char *reason;
 
@@ -2642,9 +2626,8 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 			 * of processing the split-off update, so we
 			 * don't have to do it here.
 			 */
-			ret = split_symref_update(update,
-						  referent.buf, transaction,
-						  affected_refnames, err);
+			ret = split_symref_update(update, referent.buf,
+						  transaction, err);
 			if (ret)
 				goto out;
 		}
@@ -2799,7 +2782,6 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 			       "ref_transaction_prepare");
 	size_t i;
 	int ret = 0;
-	struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
 	struct string_list refnames_to_check = STRING_LIST_INIT_NODUP;
 	char *head_ref = NULL;
 	int head_type;
@@ -2818,12 +2800,7 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 	transaction->backend_data = backend_data;
 
 	/*
-	 * Fail if a refname appears more than once in the
-	 * transaction. (If we end up splitting up any updates using
-	 * split_symref_update() or split_head_update(), those
-	 * functions will check that the new updates don't have the
-	 * same refname as any existing ones.) Also fail if any of the
-	 * updates use REF_IS_PRUNING without REF_NO_DEREF.
+	 * Fail if any of the updates use REF_IS_PRUNING without REF_NO_DEREF.
 	 */
 	for (i = 0; i < transaction->nr; i++) {
 		struct ref_update *update = transaction->updates[i];
@@ -2831,16 +2808,6 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 		if ((update->flags & REF_IS_PRUNING) &&
 		    !(update->flags & REF_NO_DEREF))
 			BUG("REF_IS_PRUNING set without REF_NO_DEREF");
-
-		if (update->flags & REF_LOG_ONLY)
-			continue;
-
-		string_list_append(&affected_refnames, update->refname);
-	}
-	string_list_sort(&affected_refnames);
-	if (ref_update_reject_duplicates(&affected_refnames, err)) {
-		ret = TRANSACTION_GENERIC_ERROR;
-		goto cleanup;
 	}
 
 	/*
@@ -2882,7 +2849,7 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 
 		ret = lock_ref_for_update(refs, update, transaction,
 					  head_ref, &refnames_to_check,
-					  &affected_refnames, err);
+					  err);
 		if (ret)
 			goto cleanup;
 
@@ -2929,7 +2896,7 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 	 * So instead, we accept the race for now.
 	 */
 	if (refs_verify_refnames_available(refs->packed_ref_store, &refnames_to_check,
-					   &affected_refnames, NULL, 0, err)) {
+					   &transaction->refnames, NULL, 0, err)) {
 		ret = TRANSACTION_NAME_CONFLICT;
 		goto cleanup;
 	}
@@ -2975,7 +2942,6 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 
 cleanup:
 	free(head_ref);
-	string_list_clear(&affected_refnames, 0);
 	string_list_clear(&refnames_to_check, 0);
 
 	if (ret)
@@ -3050,13 +3016,8 @@ static int files_transaction_finish_initial(struct files_ref_store *refs,
 	if (transaction->state != REF_TRANSACTION_PREPARED)
 		BUG("commit called for transaction that is not prepared");
 
-	/* Fail if a refname appears more than once in the transaction: */
-	for (i = 0; i < transaction->nr; i++)
-		if (!(transaction->updates[i]->flags & REF_LOG_ONLY))
-			string_list_append(&affected_refnames,
-					   transaction->updates[i]->refname);
-	string_list_sort(&affected_refnames);
-	if (ref_update_reject_duplicates(&affected_refnames, err)) {
+	string_list_sort(&transaction->refnames);
+	if (ref_update_reject_duplicates(&transaction->refnames, err)) {
 		ret = TRANSACTION_GENERIC_ERROR;
 		goto cleanup;
 	}
@@ -3074,7 +3035,7 @@ static int files_transaction_finish_initial(struct files_ref_store *refs,
 	 * that we are creating already exists.
 	 */
 	if (refs_for_each_rawref(&refs->base, ref_present,
-				 &affected_refnames))
+				 &transaction->refnames))
 		BUG("initial ref transaction called with existing refs");
 
 	packed_transaction = ref_store_transaction_begin(refs->packed_ref_store,
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index f4c82ba2c7..19220d2e99 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -1622,8 +1622,6 @@ int is_packed_transaction_needed(struct ref_store *ref_store,
 struct packed_transaction_backend_data {
 	/* True iff the transaction owns the packed-refs lock. */
 	int own_lock;
-
-	struct string_list updates;
 };
 
 static void packed_transaction_cleanup(struct packed_ref_store *refs,
@@ -1632,8 +1630,6 @@ static void packed_transaction_cleanup(struct packed_ref_store *refs,
 	struct packed_transaction_backend_data *data = transaction->backend_data;
 
 	if (data) {
-		string_list_clear(&data->updates, 0);
-
 		if (is_tempfile_active(refs->tempfile))
 			delete_tempfile(&refs->tempfile);
 
@@ -1658,7 +1654,6 @@ static int packed_transaction_prepare(struct ref_store *ref_store,
 			REF_STORE_READ | REF_STORE_WRITE | REF_STORE_ODB,
 			"ref_transaction_prepare");
 	struct packed_transaction_backend_data *data;
-	size_t i;
 	int ret = TRANSACTION_GENERIC_ERROR;
 
 	/*
@@ -1671,34 +1666,16 @@ static int packed_transaction_prepare(struct ref_store *ref_store,
 	 */
 
 	CALLOC_ARRAY(data, 1);
-	string_list_init_nodup(&data->updates);
 
 	transaction->backend_data = data;
 
-	/*
-	 * Stick the updates in a string list by refname so that we
-	 * can sort them:
-	 */
-	for (i = 0; i < transaction->nr; i++) {
-		struct ref_update *update = transaction->updates[i];
-		struct string_list_item *item =
-			string_list_append(&data->updates, update->refname);
-
-		/* Store a pointer to update in item->util: */
-		item->util = update;
-	}
-	string_list_sort(&data->updates);
-
-	if (ref_update_reject_duplicates(&data->updates, err))
-		goto failure;
-
 	if (!is_lock_file_locked(&refs->lock)) {
 		if (packed_refs_lock(ref_store, 0, err))
 			goto failure;
 		data->own_lock = 1;
 	}
 
-	if (write_with_updates(refs, &data->updates, err))
+	if (write_with_updates(refs, &transaction->refnames, err))
 		goto failure;
 
 	transaction->state = REF_TRANSACTION_PREPARED;
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index e5862757a7..92db793026 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -3,6 +3,7 @@
 
 #include "refs.h"
 #include "iterator.h"
+#include "string-list.h"
 
 struct fsck_options;
 struct ref_transaction;
@@ -198,6 +199,7 @@ enum ref_transaction_state {
 struct ref_transaction {
 	struct ref_store *ref_store;
 	struct ref_update **updates;
+	struct string_list refnames;
 	size_t alloc;
 	size_t nr;
 	enum ref_transaction_state state;
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index ae434cd248..a92c9a2f4f 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1076,7 +1076,6 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 	struct reftable_ref_store *refs =
 		reftable_be_downcast(ref_store, REF_STORE_WRITE|REF_STORE_MAIN, "ref_transaction_prepare");
 	struct strbuf referent = STRBUF_INIT, head_referent = STRBUF_INIT;
-	struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
 	struct string_list refnames_to_check = STRING_LIST_INIT_NODUP;
 	struct reftable_transaction_data *tx_data = NULL;
 	struct reftable_backend *be;
@@ -1101,10 +1100,6 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 						 transaction->updates[i], err);
 		if (ret)
 			goto done;
-
-		if (!(transaction->updates[i]->flags & REF_LOG_ONLY))
-			string_list_append(&affected_refnames,
-					   transaction->updates[i]->refname);
 	}
 
 	/*
@@ -1116,17 +1111,6 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 		tx_data->args[i].updates_alloc = tx_data->args[i].updates_expected;
 	}
 
-	/*
-	 * Fail if a refname appears more than once in the transaction.
-	 * This code is taken from the files backend and is a good candidate to
-	 * be moved into the generic layer.
-	 */
-	string_list_sort(&affected_refnames);
-	if (ref_update_reject_duplicates(&affected_refnames, err)) {
-		ret = TRANSACTION_GENERIC_ERROR;
-		goto done;
-	}
-
 	/*
 	 * TODO: it's dubious whether we should reload the stack that "HEAD"
 	 * belongs to or not. In theory, it may happen that we only modify
@@ -1194,14 +1178,12 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 		    !(u->flags & REF_LOG_ONLY) &&
 		    !(u->flags & REF_UPDATE_VIA_HEAD) &&
 		    !strcmp(rewritten_ref, head_referent.buf)) {
-			struct ref_update *new_update;
-
 			/*
 			 * First make sure that HEAD is not already in the
 			 * transaction. This check is O(lg N) in the transaction
 			 * size, but it happens at most once per transaction.
 			 */
-			if (string_list_has_string(&affected_refnames, "HEAD")) {
+			if (string_list_has_string(&transaction->refnames, "HEAD")) {
 				/* An entry already existed */
 				strbuf_addf(err,
 					    _("multiple updates for 'HEAD' (including one "
@@ -1211,12 +1193,11 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 				goto done;
 			}
 
-			new_update = ref_transaction_add_update(
-					transaction, "HEAD",
-					u->flags | REF_LOG_ONLY | REF_NO_DEREF,
-					&u->new_oid, &u->old_oid, NULL, NULL, NULL,
-					u->msg);
-			string_list_insert(&affected_refnames, new_update->refname);
+			ref_transaction_add_update(
+				transaction, "HEAD",
+				u->flags | REF_LOG_ONLY | REF_NO_DEREF,
+				&u->new_oid, &u->old_oid, NULL, NULL, NULL,
+				u->msg);
 		}
 
 		ret = reftable_backend_read_ref(be, rewritten_ref,
@@ -1281,6 +1262,15 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 				if (!strcmp(rewritten_ref, "HEAD"))
 					new_flags |= REF_UPDATE_VIA_HEAD;
 
+				if (string_list_has_string(&transaction->refnames, referent.buf)) {
+					strbuf_addf(err,
+						    _("multiple updates for '%s' (including one "
+						    "via symref '%s') are not allowed"),
+						    referent.buf, u->refname);
+					ret = TRANSACTION_NAME_CONFLICT;
+					goto done;
+				}
+
 				/*
 				 * If we are updating a symref (eg. HEAD), we should also
 				 * update the branch that the symref points to.
@@ -1305,16 +1295,6 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 				 */
 				u->flags |= REF_LOG_ONLY | REF_NO_DEREF;
 				u->flags &= ~REF_HAVE_OLD;
-
-				if (string_list_has_string(&affected_refnames, new_update->refname)) {
-					strbuf_addf(err,
-						    _("multiple updates for '%s' (including one "
-						    "via symref '%s') are not allowed"),
-						    referent.buf, u->refname);
-					ret = TRANSACTION_NAME_CONFLICT;
-					goto done;
-				}
-				string_list_insert(&affected_refnames, new_update->refname);
 			}
 		}
 
@@ -1383,7 +1363,8 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 		}
 	}
 
-	ret = refs_verify_refnames_available(ref_store, &refnames_to_check, &affected_refnames, NULL,
+	ret = refs_verify_refnames_available(ref_store, &refnames_to_check,
+					     &transaction->refnames, NULL,
 					     transaction->flags & REF_TRANSACTION_FLAG_INITIAL,
 					     err);
 	if (ret < 0)
@@ -1401,7 +1382,6 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 			strbuf_addf(err, _("reftable: transaction prepare: %s"),
 				    reftable_error_str(ret));
 	}
-	string_list_clear(&affected_refnames, 0);
 	strbuf_release(&referent);
 	strbuf_release(&head_referent);
 	string_list_clear(&refnames_to_check, 0);
-- 
2.48.1
Karthik Nayak· Mar 20, 2025, 11:43 UTC · re: Karthik Nayak · lore

[PATCH v4 3/8] refs/files: remove duplicate duplicates check

Within the files reference backend's transaction's 'finish' phase, a verification step is currently performed wherein the refnames list is sorted and examined for multiple updates targeting the same refname.

It has been observed that this verification is redundant, as an identical check is already executed during the transaction's 'prepare' stage. Since the refnames list remains unmodified following the 'prepare' stage, this secondary verification can be safely eliminated.

The duplicate check has been removed accordingly, and the `ref_update_reject_duplicates()` function has been marked as static, as its usage is now confined to 'refs.c'.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 refs.c               | 9 +++++++--
 refs/files-backend.c | 6 ------
 refs/refs-internal.h | 8 --------
 3 files changed, 7 insertions(+), 16 deletions(-)
Show changes to 3 files +7 −16

refs.c, refs/files-backend.c, refs/refs-internal.h

diff --git a/refs.c b/refs.c
index 504bf2063e..61bed9672a 100644
--- a/refs.c
+++ b/refs.c
@@ -2303,8 +2303,13 @@ int refs_update_symref_extended(struct ref_store *refs, const char *ref,
 	return ret;
 }
 
-int ref_update_reject_duplicates(struct string_list *refnames,
-				 struct strbuf *err)
+/*
+ * Write an error to `err` and return a nonzero value iff the same
+ * refname appears multiple times in `refnames`. `refnames` must be
+ * sorted on entry to this function.
+ */
+static int ref_update_reject_duplicates(struct string_list *refnames,
+					struct strbuf *err)
 {
 	size_t i, n = refnames->nr;
 
diff --git a/refs/files-backend.c b/refs/files-backend.c
index 58f62ea8a3..ea023a59fc 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -3016,12 +3016,6 @@ static int files_transaction_finish_initial(struct files_ref_store *refs,
 	if (transaction->state != REF_TRANSACTION_PREPARED)
 		BUG("commit called for transaction that is not prepared");
 
-	string_list_sort(&transaction->refnames);
-	if (ref_update_reject_duplicates(&transaction->refnames, err)) {
-		ret = TRANSACTION_GENERIC_ERROR;
-		goto cleanup;
-	}
-
 	/*
 	 * It's really undefined to call this function in an active
 	 * repository or when there are existing references: we are
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 92db793026..6d3770d0cc 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -142,14 +142,6 @@ int refs_read_raw_ref(struct ref_store *ref_store, const char *refname,
 		      struct object_id *oid, struct strbuf *referent,
 		      unsigned int *type, int *failure_errno);
 
-/*
- * Write an error to `err` and return a nonzero value iff the same
- * refname appears multiple times in `refnames`. `refnames` must be
- * sorted on entry to this function.
- */
-int ref_update_reject_duplicates(struct string_list *refnames,
-				 struct strbuf *err);
-
 /*
  * Add a ref_update with the specified properties to transaction, and
  * return a pointer to the new object. This function does not verify
-- 
2.48.1
Karthik Nayak· Mar 20, 2025, 11:43 UTC · re: Karthik Nayak · lore

[PATCH v4 4/8] refs/reftable: extract code from the transaction preparation

Extract the core logic for preparing individual reference updates from `reftable_be_transaction_prepare()` into `prepare_single_update()`. This dedicated function now handles all validation and preparation steps for each reference update in the transaction, including object ID verification, HEAD reference handling, and symref processing.

The refactoring consolidates all reference update validation into a single logical block, which improves code maintainability and readability. More importantly, this restructuring lays the groundwork for implementing batched reference update support in the reftable backend, which will be introduced in a followup commit.

No functional changes are included in this commit - it is purely a code reorganization to support future enhancements.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 refs/reftable-backend.c | 463 +++++++++++++++++++++++++-----------------------
 1 file changed, 237 insertions(+), 226 deletions(-)
Show changes to refs/reftable-backend.c +237 −226
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index a92c9a2f4f..786df11a03 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1069,6 +1069,239 @@ static int queue_transaction_update(struct reftable_ref_store *refs,
 	return 0;
 }
 
+static int prepare_single_update(struct reftable_ref_store *refs,
+				 struct reftable_transaction_data *tx_data,
+				 struct ref_transaction *transaction,
+				 struct reftable_backend *be,
+				 struct ref_update *u,
+				 struct string_list *refnames_to_check,
+				 unsigned int head_type,
+				 struct strbuf *head_referent,
+				 struct strbuf *referent,
+				 struct strbuf *err)
+{
+	struct object_id current_oid = {0};
+	const char *rewritten_ref;
+	int ret = 0;
+
+	/*
+	 * There is no need to reload the respective backends here as
+	 * we have already reloaded them when preparing the transaction
+	 * update. And given that the stacks have been locked there
+	 * shouldn't have been any concurrent modifications of the
+	 * stack.
+	 */
+	ret = backend_for(&be, refs, u->refname, &rewritten_ref, 0);
+	if (ret)
+		return ret;
+
+	/* Verify that the new object ID is valid. */
+	if ((u->flags & REF_HAVE_NEW) && !is_null_oid(&u->new_oid) &&
+	    !(u->flags & REF_SKIP_OID_VERIFICATION) &&
+	    !(u->flags & REF_LOG_ONLY)) {
+		struct object *o = parse_object(refs->base.repo, &u->new_oid);
+		if (!o) {
+			strbuf_addf(err,
+				    _("trying to write ref '%s' with nonexistent object %s"),
+				    u->refname, oid_to_hex(&u->new_oid));
+			return -1;
+		}
+
+		if (o->type != OBJ_COMMIT && is_branch(u->refname)) {
+			strbuf_addf(err, _("trying to write non-commit object %s to branch '%s'"),
+				    oid_to_hex(&u->new_oid), u->refname);
+			return -1;
+		}
+	}
+
+	/*
+	 * When we update the reference that HEAD points to we enqueue
+	 * a second log-only update for HEAD so that its reflog is
+	 * updated accordingly.
+	 */
+	if (head_type == REF_ISSYMREF &&
+	    !(u->flags & REF_LOG_ONLY) &&
+	    !(u->flags & REF_UPDATE_VIA_HEAD) &&
+	    !strcmp(rewritten_ref, head_referent->buf)) {
+		/*
+		 * First make sure that HEAD is not already in the
+		 * transaction. This check is O(lg N) in the transaction
+		 * size, but it happens at most once per transaction.
+		 */
+		if (string_list_has_string(&transaction->refnames, "HEAD")) {
+			/* An entry already existed */
+			strbuf_addf(err,
+				    _("multiple updates for 'HEAD' (including one "
+				      "via its referent '%s') are not allowed"),
+				    u->refname);
+			return TRANSACTION_NAME_CONFLICT;
+		}
+
+		ref_transaction_add_update(
+			transaction, "HEAD",
+			u->flags | REF_LOG_ONLY | REF_NO_DEREF,
+			&u->new_oid, &u->old_oid, NULL, NULL, NULL,
+			u->msg);
+	}
+
+	ret = reftable_backend_read_ref(be, rewritten_ref,
+					&current_oid, referent, &u->type);
+	if (ret < 0)
+		return ret;
+	if (ret > 0 && !ref_update_expects_existing_old_ref(u)) {
+		/*
+		 * The reference does not exist, and we either have no
+		 * old object ID or expect the reference to not exist.
+		 * We can thus skip below safety checks as well as the
+		 * symref splitting. But we do want to verify that
+		 * there is no conflicting reference here so that we
+		 * can output a proper error message instead of failing
+		 * at a later point.
+		 */
+		string_list_append(refnames_to_check, u->refname);
+
+		/*
+		 * There is no need to write the reference deletion
+		 * when the reference in question doesn't exist.
+		 */
+		if ((u->flags & REF_HAVE_NEW) && !ref_update_has_null_new_value(u)) {
+			ret = queue_transaction_update(refs, tx_data, u,
+						       &current_oid, err);
+			if (ret)
+				return ret;
+		}
+
+		return 0;
+	}
+	if (ret > 0) {
+		/* The reference does not exist, but we expected it to. */
+		strbuf_addf(err, _("cannot lock ref '%s': "
+
+
+				   "unable to resolve reference '%s'"),
+			    ref_update_original_update_refname(u), u->refname);
+		return -1;
+	}
+
+	if (u->type & REF_ISSYMREF) {
+		/*
+		 * The reftable stack is locked at this point already,
+		 * so it is safe to call `refs_resolve_ref_unsafe()`
+		 * here without causing races.
+		 */
+		const char *resolved = refs_resolve_ref_unsafe(&refs->base, u->refname, 0,
+							       &current_oid, NULL);
+
+		if (u->flags & REF_NO_DEREF) {
+			if (u->flags & REF_HAVE_OLD && !resolved) {
+				strbuf_addf(err, _("cannot lock ref '%s': "
+						   "error reading reference"), u->refname);
+				return -1;
+			}
+		} else {
+			struct ref_update *new_update;
+			int new_flags;
+
+			new_flags = u->flags;
+			if (!strcmp(rewritten_ref, "HEAD"))
+				new_flags |= REF_UPDATE_VIA_HEAD;
+
+			if (string_list_has_string(&transaction->refnames, referent->buf)) {
+				strbuf_addf(err,
+					    _("multiple updates for '%s' (including one "
+					      "via symref '%s') are not allowed"),
+					    referent->buf, u->refname);
+				return TRANSACTION_NAME_CONFLICT;
+			}
+
+			/*
+			 * If we are updating a symref (eg. HEAD), we should also
+			 * update the branch that the symref points to.
+			 *
+			 * This is generic functionality, and would be better
+			 * done in refs.c, but the current implementation is
+			 * intertwined with the locking in files-backend.c.
+			 */
+			new_update = ref_transaction_add_update(
+				transaction, referent->buf, new_flags,
+				u->new_target ? NULL : &u->new_oid,
+				u->old_target ? NULL : &u->old_oid,
+				u->new_target, u->old_target,
+				u->committer_info, u->msg);
+
+			new_update->parent_update = u;
+
+			/*
+			 * Change the symbolic ref update to log only. Also, it
+			 * doesn't need to check its old OID value, as that will be
+			 * done when new_update is processed.
+			 */
+			u->flags |= REF_LOG_ONLY | REF_NO_DEREF;
+			u->flags &= ~REF_HAVE_OLD;
+		}
+	}
+
+	/*
+	 * Verify that the old object matches our expectations. Note
+	 * that the error messages here do not make a lot of sense in
+	 * the context of the reftable backend as we never lock
+	 * individual refs. But the error messages match what the files
+	 * backend returns, which keeps our tests happy.
+	 */
+	if (u->old_target) {
+		if (!(u->type & REF_ISSYMREF)) {
+			strbuf_addf(err, _("cannot lock ref '%s': "
+					   "expected symref with target '%s': "
+					   "but is a regular ref"),
+				    ref_update_original_update_refname(u),
+				    u->old_target);
+			return -1;
+		}
+
+		if (ref_update_check_old_target(referent->buf, u, err)) {
+			return -1;
+		}
+	} else if ((u->flags & REF_HAVE_OLD) && !oideq(&current_oid, &u->old_oid)) {
+		if (is_null_oid(&u->old_oid)) {
+			strbuf_addf(err, _("cannot lock ref '%s': "
+					   "reference already exists"),
+				    ref_update_original_update_refname(u));
+			return TRANSACTION_CREATE_EXISTS;
+		}
+		else if (is_null_oid(&current_oid))
+			strbuf_addf(err, _("cannot lock ref '%s': "
+					   "reference is missing but expected %s"),
+				    ref_update_original_update_refname(u),
+				    oid_to_hex(&u->old_oid));
+		else
+			strbuf_addf(err, _("cannot lock ref '%s': "
+					   "is at %s but expected %s"),
+				    ref_update_original_update_refname(u),
+				    oid_to_hex(&current_oid),
+				    oid_to_hex(&u->old_oid));
+		return TRANSACTION_NAME_CONFLICT;
+	}
+
+	/*
+	 * If all of the following conditions are true:
+	 *
+	 *   - We're not about to write a symref.
+	 *   - We're not about to write a log-only entry.
+	 *   - Old and new object ID are different.
+	 *
+	 * Then we're essentially doing a no-op update that can be
+	 * skipped. This is not only for the sake of efficiency, but
+	 * also skips writing unneeded reflog entries.
+	 */
+	if ((u->type & REF_ISSYMREF) ||
+	    (u->flags & REF_LOG_ONLY) ||
+	    (u->flags & REF_HAVE_NEW && !oideq(&current_oid, &u->new_oid)))
+		return queue_transaction_update(refs, tx_data, u,
+					       &current_oid, err);
+
+	return 0;
+}
+
 static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 					   struct ref_transaction *transaction,
 					   struct strbuf *err)
@@ -1133,234 +1366,12 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 	ret = 0;
 
 	for (i = 0; i < transaction->nr; i++) {
-		struct ref_update *u = transaction->updates[i];
-		struct object_id current_oid = {0};
-		const char *rewritten_ref;
-
-		/*
-		 * There is no need to reload the respective backends here as
-		 * we have already reloaded them when preparing the transaction
-		 * update. And given that the stacks have been locked there
-		 * shouldn't have been any concurrent modifications of the
-		 * stack.
-		 */
-		ret = backend_for(&be, refs, u->refname, &rewritten_ref, 0);
+		ret = prepare_single_update(refs, tx_data, transaction, be,
+					    transaction->updates[i],
+					    &refnames_to_check, head_type,
+					    &head_referent, &referent, err);
 		if (ret)
 			goto done;
-
-		/* Verify that the new object ID is valid. */
-		if ((u->flags & REF_HAVE_NEW) && !is_null_oid(&u->new_oid) &&
-		    !(u->flags & REF_SKIP_OID_VERIFICATION) &&
-		    !(u->flags & REF_LOG_ONLY)) {
-			struct object *o = parse_object(refs->base.repo, &u->new_oid);
-			if (!o) {
-				strbuf_addf(err,
-					    _("trying to write ref '%s' with nonexistent object %s"),
-					    u->refname, oid_to_hex(&u->new_oid));
-				ret = -1;
-				goto done;
-			}
-
-			if (o->type != OBJ_COMMIT && is_branch(u->refname)) {
-				strbuf_addf(err, _("trying to write non-commit object %s to branch '%s'"),
-					    oid_to_hex(&u->new_oid), u->refname);
-				ret = -1;
-				goto done;
-			}
-		}
-
-		/*
-		 * When we update the reference that HEAD points to we enqueue
-		 * a second log-only update for HEAD so that its reflog is
-		 * updated accordingly.
-		 */
-		if (head_type == REF_ISSYMREF &&
-		    !(u->flags & REF_LOG_ONLY) &&
-		    !(u->flags & REF_UPDATE_VIA_HEAD) &&
-		    !strcmp(rewritten_ref, head_referent.buf)) {
-			/*
-			 * First make sure that HEAD is not already in the
-			 * transaction. This check is O(lg N) in the transaction
-			 * size, but it happens at most once per transaction.
-			 */
-			if (string_list_has_string(&transaction->refnames, "HEAD")) {
-				/* An entry already existed */
-				strbuf_addf(err,
-					    _("multiple updates for 'HEAD' (including one "
-					    "via its referent '%s') are not allowed"),
-					    u->refname);
-				ret = TRANSACTION_NAME_CONFLICT;
-				goto done;
-			}
-
-			ref_transaction_add_update(
-				transaction, "HEAD",
-				u->flags | REF_LOG_ONLY | REF_NO_DEREF,
-				&u->new_oid, &u->old_oid, NULL, NULL, NULL,
-				u->msg);
-		}
-
-		ret = reftable_backend_read_ref(be, rewritten_ref,
-						&current_oid, &referent, &u->type);
-		if (ret < 0)
-			goto done;
-		if (ret > 0 && !ref_update_expects_existing_old_ref(u)) {
-			/*
-			 * The reference does not exist, and we either have no
-			 * old object ID or expect the reference to not exist.
-			 * We can thus skip below safety checks as well as the
-			 * symref splitting. But we do want to verify that
-			 * there is no conflicting reference here so that we
-			 * can output a proper error message instead of failing
-			 * at a later point.
-			 */
-			string_list_append(&refnames_to_check, u->refname);
-
-			/*
-			 * There is no need to write the reference deletion
-			 * when the reference in question doesn't exist.
-			 */
-			 if ((u->flags & REF_HAVE_NEW) && !ref_update_has_null_new_value(u)) {
-				 ret = queue_transaction_update(refs, tx_data, u,
-								&current_oid, err);
-				 if (ret)
-					 goto done;
-			 }
-
-			continue;
-		}
-		if (ret > 0) {
-			/* The reference does not exist, but we expected it to. */
-			strbuf_addf(err, _("cannot lock ref '%s': "
-				    "unable to resolve reference '%s'"),
-				    ref_update_original_update_refname(u), u->refname);
-			ret = -1;
-			goto done;
-		}
-
-		if (u->type & REF_ISSYMREF) {
-			/*
-			 * The reftable stack is locked at this point already,
-			 * so it is safe to call `refs_resolve_ref_unsafe()`
-			 * here without causing races.
-			 */
-			const char *resolved = refs_resolve_ref_unsafe(&refs->base, u->refname, 0,
-								       &current_oid, NULL);
-
-			if (u->flags & REF_NO_DEREF) {
-				if (u->flags & REF_HAVE_OLD && !resolved) {
-					strbuf_addf(err, _("cannot lock ref '%s': "
-						    "error reading reference"), u->refname);
-					ret = -1;
-					goto done;
-				}
-			} else {
-				struct ref_update *new_update;
-				int new_flags;
-
-				new_flags = u->flags;
-				if (!strcmp(rewritten_ref, "HEAD"))
-					new_flags |= REF_UPDATE_VIA_HEAD;
-
-				if (string_list_has_string(&transaction->refnames, referent.buf)) {
-					strbuf_addf(err,
-						    _("multiple updates for '%s' (including one "
-						    "via symref '%s') are not allowed"),
-						    referent.buf, u->refname);
-					ret = TRANSACTION_NAME_CONFLICT;
-					goto done;
-				}
-
-				/*
-				 * If we are updating a symref (eg. HEAD), we should also
-				 * update the branch that the symref points to.
-				 *
-				 * This is generic functionality, and would be better
-				 * done in refs.c, but the current implementation is
-				 * intertwined with the locking in files-backend.c.
-				 */
-				new_update = ref_transaction_add_update(
-					transaction, referent.buf, new_flags,
-					u->new_target ? NULL : &u->new_oid,
-					u->old_target ? NULL : &u->old_oid,
-					u->new_target, u->old_target,
-					u->committer_info, u->msg);
-
-				new_update->parent_update = u;
-
-				/*
-				 * Change the symbolic ref update to log only. Also, it
-				 * doesn't need to check its old OID value, as that will be
-				 * done when new_update is processed.
-				 */
-				u->flags |= REF_LOG_ONLY | REF_NO_DEREF;
-				u->flags &= ~REF_HAVE_OLD;
-			}
-		}
-
-		/*
-		 * Verify that the old object matches our expectations. Note
-		 * that the error messages here do not make a lot of sense in
-		 * the context of the reftable backend as we never lock
-		 * individual refs. But the error messages match what the files
-		 * backend returns, which keeps our tests happy.
-		 */
-		if (u->old_target) {
-			if (!(u->type & REF_ISSYMREF)) {
-				strbuf_addf(err, _("cannot lock ref '%s': "
-					   "expected symref with target '%s': "
-					   "but is a regular ref"),
-					    ref_update_original_update_refname(u),
-					    u->old_target);
-				ret = -1;
-				goto done;
-			}
-
-			if (ref_update_check_old_target(referent.buf, u, err)) {
-				ret = -1;
-				goto done;
-			}
-		} else if ((u->flags & REF_HAVE_OLD) && !oideq(&current_oid, &u->old_oid)) {
-			ret = TRANSACTION_NAME_CONFLICT;
-			if (is_null_oid(&u->old_oid)) {
-				strbuf_addf(err, _("cannot lock ref '%s': "
-						   "reference already exists"),
-					    ref_update_original_update_refname(u));
-				ret = TRANSACTION_CREATE_EXISTS;
-			}
-			else if (is_null_oid(&current_oid))
-				strbuf_addf(err, _("cannot lock ref '%s': "
-						   "reference is missing but expected %s"),
-					    ref_update_original_update_refname(u),
-					    oid_to_hex(&u->old_oid));
-			else
-				strbuf_addf(err, _("cannot lock ref '%s': "
-						   "is at %s but expected %s"),
-					    ref_update_original_update_refname(u),
-					    oid_to_hex(&current_oid),
-					    oid_to_hex(&u->old_oid));
-			goto done;
-		}
-
-		/*
-		 * If all of the following conditions are true:
-		 *
-		 *   - We're not about to write a symref.
-		 *   - We're not about to write a log-only entry.
-		 *   - Old and new object ID are different.
-		 *
-		 * Then we're essentially doing a no-op update that can be
-		 * skipped. This is not only for the sake of efficiency, but
-		 * also skips writing unneeded reflog entries.
-		 */
-		if ((u->type & REF_ISSYMREF) ||
-		    (u->flags & REF_LOG_ONLY) ||
-		    (u->flags & REF_HAVE_NEW && !oideq(&current_oid, &u->new_oid))) {
-			ret = queue_transaction_update(refs, tx_data, u,
-						       &current_oid, err);
-			if (ret)
-				goto done;
-		}
 	}
 
 	ret = refs_verify_refnames_available(ref_store, &refnames_to_check,
-- 
2.48.1
Karthik Nayak· Mar 20, 2025, 11:44 UTC · re: Karthik Nayak · lore

[PATCH v4 6/8] refs: implement batch reference update support

Git supports making reference updates with or without transactions. Updates with transactions are generally better optimized. But transactions are all or nothing. This means, if a user wants to batch updates to take advantage of the optimizations without the hard requirement that all updates must succeed, there is no way currently to do so. Particularly with the reftable backend where batching multiple reference updates is more efficient than performing them sequentially.

Introduce batched update support with a new flag, 'REF_TRANSACTION_ALLOW_FAILURE'. Batched updates while different from transactions, use the transaction infrastructure under the hood. When enabled, this flag allows individual reference updates that would typically cause the entire transaction to fail due to non-system-related errors to be marked as rejected while permitting other updates to proceed. System errors referred by 'REF_TRANSACTION_ERROR_GENERIC' continue to result in the entire transaction failing. This approach enhances flexibility while preserving transactional integrity where necessary.

The implementation introduces several key components:
  - Add 'rejection_err' field to struct `ref_update` to track failed
    updates with failure reason.
  - Add a new struct `ref_transaction_rejections` and a field within
    `ref_transaction` to this struct to allow quick iteration over
    rejected updates.
  - Modify reference backends (files, packed, reftable) to handle
    partial transactions by using `ref_transaction_set_rejected()`
    instead of failing the entire transaction when
    `REF_TRANSACTION_ALLOW_FAILURE` is set.
  - Add `ref_transaction_for_each_rejected_update()` to let callers
    examine which updates were rejected and why.

This foundational change enables batched update support throughout the reference subsystem. A following commit will expose this capability to users by adding a `--batch-updates` flag to 'git-update-ref(1)', providing both a user-facing feature and a testable implementation.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 refs.c                  | 61 +++++++++++++++++++++++++++++++++++++++++++++++++
 refs.h                  | 22 ++++++++++++++++++
 refs/files-backend.c    | 12 +++++++++-
 refs/packed-backend.c   | 27 ++++++++++++++++++++--
 refs/refs-internal.h    | 26 +++++++++++++++++++++
 refs/reftable-backend.c | 12 +++++++++-
 6 files changed, 156 insertions(+), 4 deletions(-)
Show changes to 6 files +156 −4

refs.c, refs.h, refs/files-backend.c, refs/packed-backend.c, refs/refs-internal.h, refs/reftable-backend.c

diff --git a/refs.c b/refs.c
index 3d0b53d56e..b34ec198f5 100644
--- a/refs.c
+++ b/refs.c
@@ -1176,6 +1176,10 @@ struct ref_transaction *ref_store_transaction_begin(struct ref_store *refs,
 	tr->ref_store = refs;
 	tr->flags = flags;
 	string_list_init_dup(&tr->refnames);
+
+	if (flags & REF_TRANSACTION_ALLOW_FAILURE)
+		CALLOC_ARRAY(tr->rejections, 1);
+
 	return tr;
 }
 
@@ -1206,11 +1210,45 @@ void ref_transaction_free(struct ref_transaction *transaction)
 		free((char *)transaction->updates[i]->old_target);
 		free(transaction->updates[i]);
 	}
+
+	if (transaction->rejections)
+		free(transaction->rejections->update_indices);
+	free(transaction->rejections);
+
 	string_list_clear(&transaction->refnames, 0);
 	free(transaction->updates);
 	free(transaction);
 }
 
+int ref_transaction_maybe_set_rejected(struct ref_transaction *transaction,
+				       size_t update_idx,
+				       enum ref_transaction_error err)
+{
+	if (update_idx >= transaction->nr)
+		BUG("trying to set rejection on invalid update index");
+
+	if (!(transaction->flags & REF_TRANSACTION_ALLOW_FAILURE))
+		return 0;
+
+	if (!transaction->rejections)
+		BUG("transaction not inititalized with failure support");
+
+	/*
+	 * Don't accept generic errors, since these errors are not user
+	 * input related.
+	 */
+	if (err == REF_TRANSACTION_ERROR_GENERIC)
+		return 0;
+
+	transaction->updates[update_idx]->rejection_err = err;
+	ALLOC_GROW(transaction->rejections->update_indices,
+		   transaction->rejections->nr + 1,
+		   transaction->rejections->alloc);
+	transaction->rejections->update_indices[transaction->rejections->nr++] = update_idx;
+
+	return 1;
+}
+
 struct ref_update *ref_transaction_add_update(
 		struct ref_transaction *transaction,
 		const char *refname, unsigned int flags,
@@ -1236,6 +1274,7 @@ struct ref_update *ref_transaction_add_update(
 	transaction->updates[transaction->nr++] = update;
 
 	update->flags = flags;
+	update->rejection_err = 0;
 
 	update->new_target = xstrdup_or_null(new_target);
 	update->old_target = xstrdup_or_null(old_target);
@@ -2728,6 +2767,28 @@ void ref_transaction_for_each_queued_update(struct ref_transaction *transaction,
 	}
 }
 
+void ref_transaction_for_each_rejected_update(struct ref_transaction *transaction,
+					      ref_transaction_for_each_rejected_update_fn cb,
+					      void *cb_data)
+{
+	if (!transaction->rejections)
+		return;
+
+	for (size_t i = 0; i < transaction->rejections->nr; i++) {
+		size_t update_index = transaction->rejections->update_indices[i];
+		struct ref_update *update = transaction->updates[update_index];
+
+		if (!update->rejection_err)
+			continue;
+
+		cb(update->refname,
+		   (update->flags & REF_HAVE_OLD) ? &update->old_oid : NULL,
+		   (update->flags & REF_HAVE_NEW) ? &update->new_oid : NULL,
+		   update->old_target, update->new_target,
+		   update->rejection_err, cb_data);
+	}
+}
+
 int refs_delete_refs(struct ref_store *refs, const char *logmsg,
 		     struct string_list *refnames, unsigned int flags)
 {
diff --git a/refs.h b/refs.h
index dcd83e81e2..591b703d59 100644
--- a/refs.h
+++ b/refs.h
@@ -673,6 +673,13 @@ enum ref_transaction_flag {
 	 * either be absent or null_oid.
 	 */
 	REF_TRANSACTION_FLAG_INITIAL = (1 << 0),
+
+	/*
+	 * The transaction mechanism by default fails all updates if any conflict
+	 * is detected. This flag allows transactions to partially apply updates
+	 * while rejecting updates which do not match the expected state.
+	 */
+	REF_TRANSACTION_ALLOW_FAILURE = (1 << 1),
 };
 
 /*
@@ -903,6 +910,21 @@ void ref_transaction_for_each_queued_update(struct ref_transaction *transaction,
 					    ref_transaction_for_each_queued_update_fn cb,
 					    void *cb_data);
 
+/*
+ * Execute the given callback function for each of the reference updates which
+ * have been rejected in the given transaction.
+ */
+typedef void ref_transaction_for_each_rejected_update_fn(const char *refname,
+							 const struct object_id *old_oid,
+							 const struct object_id *new_oid,
+							 const char *old_target,
+							 const char *new_target,
+							 enum ref_transaction_error err,
+							 void *cb_data);
+void ref_transaction_for_each_rejected_update(struct ref_transaction *transaction,
+					      ref_transaction_for_each_rejected_update_fn cb,
+					      void *cb_data);
+
 /*
  * Free `*transaction` and all associated data.
  */
diff --git a/refs/files-backend.c b/refs/files-backend.c
index 4f27f7652c..be758ffff5 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -2852,8 +2852,15 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 		ret = lock_ref_for_update(refs, update, transaction,
 					  head_ref, &refnames_to_check,
 					  err);
-		if (ret)
+		if (ret) {
+			if (ref_transaction_maybe_set_rejected(transaction, i, ret)) {
+				strbuf_setlen(err, 0);
+				ret = 0;
+
+				continue;
+			}
 			goto cleanup;
+		}
 
 		if (update->flags & REF_DELETING &&
 		    !(update->flags & REF_LOG_ONLY) &&
@@ -3151,6 +3158,9 @@ static int files_transaction_finish(struct ref_store *ref_store,
 		struct ref_update *update = transaction->updates[i];
 		struct ref_lock *lock = update->backend_data;
 
+		if (update->rejection_err)
+			continue;
+
 		if (update->flags & REF_NEEDS_COMMIT ||
 		    update->flags & REF_LOG_ONLY) {
 			if (parse_and_write_reflog(refs, update, lock, err)) {
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index d90bd815a3..7bf57ca948 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -1327,10 +1327,11 @@ static int packed_ref_store_remove_on_disk(struct ref_store *ref_store,
  * remain locked when it is done.
  */
 static enum ref_transaction_error write_with_updates(struct packed_ref_store *refs,
-						     struct string_list *updates,
+						     struct ref_transaction *transaction,
 						     struct strbuf *err)
 {
 	enum ref_transaction_error ret = REF_TRANSACTION_ERROR_GENERIC;
+	struct string_list *updates = &transaction->refnames;
 	struct ref_iterator *iter = NULL;
 	size_t i;
 	int ok;
@@ -1411,6 +1412,13 @@ static enum ref_transaction_error write_with_updates(struct packed_ref_store *re
 						    "reference already exists",
 						    update->refname);
 					ret = REF_TRANSACTION_ERROR_CREATE_EXISTS;
+
+					if (ref_transaction_maybe_set_rejected(transaction, i, ret)) {
+						strbuf_setlen(err, 0);
+						ret = 0;
+						continue;
+					}
+
 					goto error;
 				} else if (!oideq(&update->old_oid, iter->oid)) {
 					strbuf_addf(err, "cannot update ref '%s': "
@@ -1419,6 +1427,13 @@ static enum ref_transaction_error write_with_updates(struct packed_ref_store *re
 						    oid_to_hex(iter->oid),
 						    oid_to_hex(&update->old_oid));
 					ret = REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE;
+
+					if (ref_transaction_maybe_set_rejected(transaction, i, ret)) {
+						strbuf_setlen(err, 0);
+						ret = 0;
+						continue;
+					}
+
 					goto error;
 				}
 			}
@@ -1456,6 +1471,13 @@ static enum ref_transaction_error write_with_updates(struct packed_ref_store *re
 					    update->refname,
 					    oid_to_hex(&update->old_oid));
 				ret = REF_TRANSACTION_ERROR_NONEXISTENT_REF;
+
+				if (ref_transaction_maybe_set_rejected(transaction, i, ret)) {
+					strbuf_setlen(err, 0);
+					ret = 0;
+					continue;
+				}
+
 				goto error;
 			}
 		}
@@ -1521,6 +1543,7 @@ static enum ref_transaction_error write_with_updates(struct packed_ref_store *re
 write_error:
 	strbuf_addf(err, "error writing to %s: %s",
 		    get_tempfile_path(refs->tempfile), strerror(errno));
+	ret = REF_TRANSACTION_ERROR_GENERIC;
 
 error:
 	ref_iterator_free(iter);
@@ -1679,7 +1702,7 @@ static int packed_transaction_prepare(struct ref_store *ref_store,
 		data->own_lock = 1;
 	}
 
-	ret = write_with_updates(refs, &transaction->refnames, err);
+	ret = write_with_updates(refs, transaction, err);
 	if (ret)
 		goto failure;
 
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 3f1d19abd9..73a5379b73 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -123,6 +123,12 @@ struct ref_update {
 	 */
 	uint64_t index;
 
+	/*
+	 * Used in batched reference updates to mark if a given update
+	 * was rejected.
+	 */
+	enum ref_transaction_error rejection_err;
+
 	/*
 	 * If this ref_update was split off of a symref update via
 	 * split_symref_update(), then this member points at that
@@ -142,6 +148,13 @@ int refs_read_raw_ref(struct ref_store *ref_store, const char *refname,
 		      struct object_id *oid, struct strbuf *referent,
 		      unsigned int *type, int *failure_errno);
 
+/*
+ * Mark a given update as rejected with a given reason.
+ */
+int ref_transaction_maybe_set_rejected(struct ref_transaction *transaction,
+				       size_t update_idx,
+				       enum ref_transaction_error err);
+
 /*
  * Add a ref_update with the specified properties to transaction, and
  * return a pointer to the new object. This function does not verify
@@ -183,6 +196,18 @@ enum ref_transaction_state {
 	REF_TRANSACTION_CLOSED   = 2
 };
 
+/*
+ * Data structure to hold indices of updates which were rejected, for batched
+ * reference updates. While the updates themselves hold the rejection error,
+ * this structure allows a transaction to iterate only over the rejected
+ * updates.
+ */
+struct ref_transaction_rejections {
+	size_t *update_indices;
+	size_t alloc;
+	size_t nr;
+};
+
 /*
  * Data structure for holding a reference transaction, which can
  * consist of checks and updates to multiple references, carried out
@@ -195,6 +220,7 @@ struct ref_transaction {
 	size_t alloc;
 	size_t nr;
 	enum ref_transaction_state state;
+	struct ref_transaction_rejections *rejections;
 	void *backend_data;
 	unsigned int flags;
 	uint64_t max_index;
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index bd6b042103..ed65225763 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1371,8 +1371,15 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 					    transaction->updates[i],
 					    &refnames_to_check, head_type,
 					    &head_referent, &referent, err);
-		if (ret)
+		if (ret) {
+			if (ref_transaction_maybe_set_rejected(transaction, i, ret)) {
+				strbuf_setlen(err, 0);
+				ret = 0;
+
+				continue;
+			}
 			goto done;
+		}
 	}
 
 	ret = refs_verify_refnames_available(ref_store, &refnames_to_check,
@@ -1454,6 +1461,9 @@ static int write_transaction_table(struct reftable_writer *writer, void *cb_data
 		struct reftable_transaction_update *tx_update = &arg->updates[i];
 		struct ref_update *u = tx_update->update;
 
+		if (u->rejection_err)
+			continue;
+
 		/*
 		 * Write a reflog entry when updating a ref to point to
 		 * something new in either of the following cases:
-- 
2.48.1
Patrick Steinhardt· Mar 20, 2025, 20:26 UTC · re: Karthik Nayak · lore

Re: [PATCH v4 6/8] refs: implement batch reference update support

On Thu, Mar 20, 2025 at 12:44:01PM +0100, Karthik Nayak wrote:
Show 46 quoted lines
> diff --git a/refs.c b/refs.c
> index 3d0b53d56e..b34ec198f5 100644
> --- a/refs.c
> +++ b/refs.c
> @@ -1206,11 +1210,45 @@ void ref_transaction_free(struct ref_transaction *transaction)
>  		free((char *)transaction->updates[i]->old_target);
>  		free(transaction->updates[i]);
>  	}
> +
> +	if (transaction->rejections)
> +		free(transaction->rejections->update_indices);
> +	free(transaction->rejections);
> +
>  	string_list_clear(&transaction->refnames, 0);
>  	free(transaction->updates);
>  	free(transaction);
>  }
>  
> +int ref_transaction_maybe_set_rejected(struct ref_transaction *transaction,
> +				       size_t update_idx,
> +				       enum ref_transaction_error err)
> +{
> +	if (update_idx >= transaction->nr)
> +		BUG("trying to set rejection on invalid update index");
> +
> +	if (!(transaction->flags & REF_TRANSACTION_ALLOW_FAILURE))
> +		return 0;
> +
> +	if (!transaction->rejections)
> +		BUG("transaction not inititalized with failure support");
> +
> +	/*
> +	 * Don't accept generic errors, since these errors are not user
> +	 * input related.
> +	 */
> +	if (err == REF_TRANSACTION_ERROR_GENERIC)
> +		return 0;
> +
> +	transaction->updates[update_idx]->rejection_err = err;
> +	ALLOC_GROW(transaction->rejections->update_indices,
> +		   transaction->rejections->nr + 1,
> +		   transaction->rejections->alloc);
> +	transaction->rejections->update_indices[transaction->rejections->nr++] = update_idx;
> +
> +	return 1;
> +}

If we had a `struct ref_update_rejection` we could store the update index and rejection errors in the same location, which might be a bit easier to reason about.

Show 24 quoted lines
> diff --git a/refs/packed-backend.c b/refs/packed-backend.c
> index d90bd815a3..7bf57ca948 100644
> --- a/refs/packed-backend.c
> +++ b/refs/packed-backend.c
> @@ -1327,10 +1327,11 @@ static int packed_ref_store_remove_on_disk(struct ref_store *ref_store,
>   * remain locked when it is done.
>   */
>  static enum ref_transaction_error write_with_updates(struct packed_ref_store *refs,
> -						     struct string_list *updates,
> +						     struct ref_transaction *transaction,
>  						     struct strbuf *err)
>  {
>  	enum ref_transaction_error ret = REF_TRANSACTION_ERROR_GENERIC;
> +	struct string_list *updates = &transaction->refnames;
>  	struct ref_iterator *iter = NULL;
>  	size_t i;
>  	int ok;
> @@ -1411,6 +1412,13 @@ static enum ref_transaction_error write_with_updates(struct packed_ref_store *re
>  						    "reference already exists",
>  						    update->refname);
>  					ret = REF_TRANSACTION_ERROR_CREATE_EXISTS;
> +
> +					if (ref_transaction_maybe_set_rejected(transaction, i, ret)) {
> +						strbuf_setlen(err, 0);
Nit: you can use `strbuf_reset()` for this and other instances.
Patrick
Karthik Nayak· Mar 24, 2025, 14:54 UTC · re: Patrick Steinhardt · lore

Re: [PATCH v4 6/8] refs: implement batch reference update support

Patrick Steinhardt <ps@pks.im> writes:
Show 52 quoted lines
> On Thu, Mar 20, 2025 at 12:44:01PM +0100, Karthik Nayak wrote:
>> diff --git a/refs.c b/refs.c
>> index 3d0b53d56e..b34ec198f5 100644
>> --- a/refs.c
>> +++ b/refs.c
>> @@ -1206,11 +1210,45 @@ void ref_transaction_free(struct ref_transaction *transaction)
>>  		free((char *)transaction->updates[i]->old_target);
>>  		free(transaction->updates[i]);
>>  	}
>> +
>> +	if (transaction->rejections)
>> +		free(transaction->rejections->update_indices);
>> +	free(transaction->rejections);
>> +
>>  	string_list_clear(&transaction->refnames, 0);
>>  	free(transaction->updates);
>>  	free(transaction);
>>  }
>>
>> +int ref_transaction_maybe_set_rejected(struct ref_transaction *transaction,
>> +				       size_t update_idx,
>> +				       enum ref_transaction_error err)
>> +{
>> +	if (update_idx >= transaction->nr)
>> +		BUG("trying to set rejection on invalid update index");
>> +
>> +	if (!(transaction->flags & REF_TRANSACTION_ALLOW_FAILURE))
>> +		return 0;
>> +
>> +	if (!transaction->rejections)
>> +		BUG("transaction not inititalized with failure support");
>> +
>> +	/*
>> +	 * Don't accept generic errors, since these errors are not user
>> +	 * input related.
>> +	 */
>> +	if (err == REF_TRANSACTION_ERROR_GENERIC)
>> +		return 0;
>> +
>> +	transaction->updates[update_idx]->rejection_err = err;
>> +	ALLOC_GROW(transaction->rejections->update_indices,
>> +		   transaction->rejections->nr + 1,
>> +		   transaction->rejections->alloc);
>> +	transaction->rejections->update_indices[transaction->rejections->nr++] = update_idx;
>> +
>> +	return 1;
>> +}
>
> If we had a `struct ref_update_rejection` we could store the update
> index and rejection errors in the same location, which might be a bit
> easier to reason about.
>

I struggled with this a bit, I was thinking the same at the start. But then I was also thinking that a rejection is specific to an update so it should lie in `ref_update`, however tracking failed updates in a transaction is specific to a transaction and should lie in `ref_transaction`. It probably would be easier code-wise to have them both in the same place, but it didn't feel like the correct place.

Show 27 quoted lines
>> diff --git a/refs/packed-backend.c b/refs/packed-backend.c
>> index d90bd815a3..7bf57ca948 100644
>> --- a/refs/packed-backend.c
>> +++ b/refs/packed-backend.c
>> @@ -1327,10 +1327,11 @@ static int packed_ref_store_remove_on_disk(struct ref_store *ref_store,
>>   * remain locked when it is done.
>>   */
>>  static enum ref_transaction_error write_with_updates(struct packed_ref_store *refs,
>> -						     struct string_list *updates,
>> +						     struct ref_transaction *transaction,
>>  						     struct strbuf *err)
>>  {
>>  	enum ref_transaction_error ret = REF_TRANSACTION_ERROR_GENERIC;
>> +	struct string_list *updates = &transaction->refnames;
>>  	struct ref_iterator *iter = NULL;
>>  	size_t i;
>>  	int ok;
>> @@ -1411,6 +1412,13 @@ static enum ref_transaction_error write_with_updates(struct packed_ref_store *re
>>  						    "reference already exists",
>>  						    update->refname);
>>  					ret = REF_TRANSACTION_ERROR_CREATE_EXISTS;
>> +
>> +					if (ref_transaction_maybe_set_rejected(transaction, i, ret)) {
>> +						strbuf_setlen(err, 0);
>
> Nit: you can use `strbuf_reset()` for this and other instances.
>
Yes, indeed, will change!
> Patrick
Karthik Nayak· Mar 20, 2025, 11:44 UTC · re: Karthik Nayak · lore

[PATCH v4 5/8] refs: introduce enum-based transaction error types

Replace preprocessor-defined transaction errors with a strongly-typed enum `ref_transaction_error`. This change:

  - Improves type safety and function signature clarity.
  - Makes error handling more explicit and discoverable.
  - Maintains existing error cases, while adding new error cases for
    common scenarios.

This refactoring paves the way for more comprehensive error handling which we will utilize in the upcoming commits to add batch reference update support.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 builtin/fetch.c         |   2 +-
 refs.c                  |  49 ++++++------
 refs.h                  |  54 ++++++++-----
 refs/files-backend.c    | 202 ++++++++++++++++++++++++------------------------
 refs/packed-backend.c   |  23 +++---
 refs/refs-internal.h    |   5 +-
 refs/reftable-backend.c |  64 +++++++--------
 7 files changed, 213 insertions(+), 186 deletions(-)
Show changes to 7 files +213 −186

builtin/fetch.c, refs.c, refs.h, refs/files-backend.c, refs/packed-backend.c, refs/refs-internal.h, refs/reftable-backend.c

diff --git a/builtin/fetch.c b/builtin/fetch.c
index 95fd0018b9..7615c17faf 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -687,7 +687,7 @@ static int s_update_ref(const char *action,
 		switch (ref_transaction_commit(our_transaction, &err)) {
 		case 0:
 			break;
-		case TRANSACTION_NAME_CONFLICT:
+		case REF_TRANSACTION_ERROR_NAME_CONFLICT:
 			ret = STORE_REF_ERROR_DF_CONFLICT;
 			goto out;
 		default:
diff --git a/refs.c b/refs.c
index 61bed9672a..3d0b53d56e 100644
--- a/refs.c
+++ b/refs.c
@@ -2271,7 +2271,7 @@ int refs_update_symref_extended(struct ref_store *refs, const char *ref,
 					   REF_NO_DEREF, logmsg, &err))
 			goto error_return;
 		prepret = ref_transaction_prepare(transaction, &err);
-		if (prepret && prepret != TRANSACTION_CREATE_EXISTS)
+		if (prepret && prepret != REF_TRANSACTION_ERROR_CREATE_EXISTS)
 			goto error_return;
 	} else {
 		if (ref_transaction_update(transaction, ref, NULL, NULL,
@@ -2289,7 +2289,7 @@ int refs_update_symref_extended(struct ref_store *refs, const char *ref,
 		}
 	}
 
-	if (prepret == TRANSACTION_CREATE_EXISTS)
+	if (prepret == REF_TRANSACTION_ERROR_CREATE_EXISTS)
 		goto cleanup;
 
 	if (ref_transaction_commit(transaction, &err))
@@ -2425,7 +2425,7 @@ int ref_transaction_prepare(struct ref_transaction *transaction,
 
 	string_list_sort(&transaction->refnames);
 	if (ref_update_reject_duplicates(&transaction->refnames, err))
-		return TRANSACTION_GENERIC_ERROR;
+		return REF_TRANSACTION_ERROR_GENERIC;
 
 	ret = refs->be->transaction_prepare(refs, transaction, err);
 	if (ret)
@@ -2497,19 +2497,19 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 	return ret;
 }
 
-int refs_verify_refnames_available(struct ref_store *refs,
-				   const struct string_list *refnames,
-				   const struct string_list *extras,
-				   const struct string_list *skip,
-				   unsigned int initial_transaction,
-				   struct strbuf *err)
+enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs,
+					  const struct string_list *refnames,
+					  const struct string_list *extras,
+					  const struct string_list *skip,
+					  unsigned int initial_transaction,
+					  struct strbuf *err)
 {
 	struct strbuf dirname = STRBUF_INIT;
 	struct strbuf referent = STRBUF_INIT;
 	struct string_list_item *item;
 	struct ref_iterator *iter = NULL;
 	struct strset dirnames;
-	int ret = -1;
+	int ret = REF_TRANSACTION_ERROR_NAME_CONFLICT;
 
 	/*
 	 * For the sake of comments in this function, suppose that
@@ -2625,12 +2625,13 @@ int refs_verify_refnames_available(struct ref_store *refs,
 	return ret;
 }
 
-int refs_verify_refname_available(struct ref_store *refs,
-				  const char *refname,
-				  const struct string_list *extras,
-				  const struct string_list *skip,
-				  unsigned int initial_transaction,
-				  struct strbuf *err)
+enum ref_transaction_error refs_verify_refname_available(
+	struct ref_store *refs,
+	const char *refname,
+	const struct string_list *extras,
+	const struct string_list *skip,
+	unsigned int initial_transaction,
+	struct strbuf *err)
 {
 	struct string_list_item item = { .string = (char *) refname };
 	struct string_list refnames = {
@@ -2818,8 +2819,9 @@ int ref_update_has_null_new_value(struct ref_update *update)
 	return !update->new_target && is_null_oid(&update->new_oid);
 }
 
-int ref_update_check_old_target(const char *referent, struct ref_update *update,
-				struct strbuf *err)
+enum ref_transaction_error ref_update_check_old_target(const char *referent,
+						       struct ref_update *update,
+						       struct strbuf *err)
 {
 	if (!update->old_target)
 		BUG("called without old_target set");
@@ -2827,17 +2829,18 @@ int ref_update_check_old_target(const char *referent, struct ref_update *update,
 	if (!strcmp(referent, update->old_target))
 		return 0;
 
-	if (!strcmp(referent, ""))
+	if (!strcmp(referent, "")) {
 		strbuf_addf(err, "verifying symref target: '%s': "
 			    "reference is missing but expected %s",
 			    ref_update_original_update_refname(update),
 			    update->old_target);
-	else
-		strbuf_addf(err, "verifying symref target: '%s': "
-			    "is at %s but expected %s",
+		return REF_TRANSACTION_ERROR_NONEXISTENT_REF;
+	}
+
+	strbuf_addf(err, "verifying symref target: '%s': is at %s but expected %s",
 			    ref_update_original_update_refname(update),
 			    referent, update->old_target);
-	return -1;
+	return REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE;
 }
 
 struct migration_data {
diff --git a/refs.h b/refs.h
index 240e2d8537..dcd83e81e2 100644
--- a/refs.h
+++ b/refs.h
@@ -16,6 +16,29 @@ struct worktree;
 enum ref_storage_format ref_storage_format_by_name(const char *name);
 const char *ref_storage_format_to_name(enum ref_storage_format ref_storage_format);
 
+/*
+ * enum ref_transaction_error represents the following return codes:
+ * REF_TRANSACTION_ERROR_GENERIC error_code: default error code.
+ * REF_TRANSACTION_ERROR_NAME_CONFLICT error_code: ref name conflict like A vs A/B.
+ * REF_TRANSACTION_ERROR_CREATE_EXISTS error_code: ref to be created already exists.
+ * REF_TRANSACTION_ERROR_NONEXISTENT_REF error_code: ref expected but doesn't exist.
+ * REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE error_code: provided old_oid or old_target of
+ * reference doesn't match actual.
+ * REF_TRANSACTION_ERROR_INVALID_NEW_VALUE error_code: provided new_oid or new_target is
+ * invalid.
+ * REF_TRANSACTION_ERROR_EXPECTED_SYMREF error_code: expected ref to be symref, but is a
+ * regular ref.
+ */
+enum ref_transaction_error {
+	REF_TRANSACTION_ERROR_GENERIC = -1,
+	REF_TRANSACTION_ERROR_NAME_CONFLICT = -2,
+	REF_TRANSACTION_ERROR_CREATE_EXISTS = -3,
+	REF_TRANSACTION_ERROR_NONEXISTENT_REF = -4,
+	REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE = -5,
+	REF_TRANSACTION_ERROR_INVALID_NEW_VALUE = -6,
+	REF_TRANSACTION_ERROR_EXPECTED_SYMREF = -7,
+};
+
 /*
  * Resolve a reference, recursively following symbolic references.
  *
@@ -117,24 +140,24 @@ int refs_read_symbolic_ref(struct ref_store *ref_store, const char *refname,
  *
  * extras and skip must be sorted.
  */
-int refs_verify_refname_available(struct ref_store *refs,
-				  const char *refname,
-				  const struct string_list *extras,
-				  const struct string_list *skip,
-				  unsigned int initial_transaction,
-				  struct strbuf *err);
+enum ref_transaction_error refs_verify_refname_available(struct ref_store *refs,
+						 const char *refname,
+						 const struct string_list *extras,
+						 const struct string_list *skip,
+						 unsigned int initial_transaction,
+						 struct strbuf *err);
 
 /*
  * Same as `refs_verify_refname_available()`, but checking for a list of
  * refnames instead of only a single item. This is more efficient in the case
  * where one needs to check multiple refnames.
  */
-int refs_verify_refnames_available(struct ref_store *refs,
-				   const struct string_list *refnames,
-				   const struct string_list *extras,
-				   const struct string_list *skip,
-				   unsigned int initial_transaction,
-				   struct strbuf *err);
+enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs,
+					  const struct string_list *refnames,
+					  const struct string_list *extras,
+					  const struct string_list *skip,
+					  unsigned int initial_transaction,
+					  struct strbuf *err);
 
 int refs_ref_exists(struct ref_store *refs, const char *refname);
 
@@ -830,13 +853,6 @@ int ref_transaction_verify(struct ref_transaction *transaction,
 			   unsigned int flags,
 			   struct strbuf *err);
 
-/* Naming conflict (for example, the ref names A and A/B conflict). */
-#define TRANSACTION_NAME_CONFLICT -1
-/* When only creation was requested, but the ref already exists. */
-#define TRANSACTION_CREATE_EXISTS -2
-/* All other errors. */
-#define TRANSACTION_GENERIC_ERROR -3
-
 /*
  * Perform the preparatory stages of committing `transaction`. Acquire
  * any needed locks, check preconditions, etc.; basically, do as much
diff --git a/refs/files-backend.c b/refs/files-backend.c
index ea023a59fc..4f27f7652c 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -663,7 +663,7 @@ static void unlock_ref(struct ref_lock *lock)
  * broken, lock the reference anyway but clear old_oid.
  *
  * Return 0 on success. On failure, write an error message to err and
- * return TRANSACTION_NAME_CONFLICT or TRANSACTION_GENERIC_ERROR.
+ * return REF_TRANSACTION_ERROR_NAME_CONFLICT or REF_TRANSACTION_ERROR_GENERIC.
  *
  * Implementation note: This function is basically
  *
@@ -676,19 +676,20 @@ static void unlock_ref(struct ref_lock *lock)
  *   avoided, namely if we were successfully able to read the ref
  * - Generate informative error messages in the case of failure
  */
-static int lock_raw_ref(struct files_ref_store *refs,
-			const char *refname, int mustexist,
-			struct string_list *refnames_to_check,
-			const struct string_list *extras,
-			struct ref_lock **lock_p,
-			struct strbuf *referent,
-			unsigned int *type,
-			struct strbuf *err)
-{
+static enum ref_transaction_error lock_raw_ref(struct files_ref_store *refs,
+					       const char *refname,
+					       int mustexist,
+					       struct string_list *refnames_to_check,
+					       const struct string_list *extras,
+					       struct ref_lock **lock_p,
+					       struct strbuf *referent,
+					       unsigned int *type,
+					       struct strbuf *err)
+{
+	enum ref_transaction_error ret = REF_TRANSACTION_ERROR_GENERIC;
 	struct ref_lock *lock;
 	struct strbuf ref_file = STRBUF_INIT;
 	int attempts_remaining = 3;
-	int ret = TRANSACTION_GENERIC_ERROR;
 	int failure_errno;
 
 	assert(err);
@@ -728,13 +729,14 @@ static int lock_raw_ref(struct files_ref_store *refs,
 				strbuf_reset(err);
 				strbuf_addf(err, "unable to resolve reference '%s'",
 					    refname);
+				ret = REF_TRANSACTION_ERROR_NONEXISTENT_REF;
 			} else {
 				/*
 				 * The error message set by
 				 * refs_verify_refname_available() is
 				 * OK.
 				 */
-				ret = TRANSACTION_NAME_CONFLICT;
+				ret = REF_TRANSACTION_ERROR_NAME_CONFLICT;
 			}
 		} else {
 			/*
@@ -788,6 +790,7 @@ static int lock_raw_ref(struct files_ref_store *refs,
 				/* Garden variety missing reference. */
 				strbuf_addf(err, "unable to resolve reference '%s'",
 					    refname);
+				ret = REF_TRANSACTION_ERROR_NONEXISTENT_REF;
 				goto error_return;
 			} else {
 				/*
@@ -820,6 +823,7 @@ static int lock_raw_ref(struct files_ref_store *refs,
 				/* Garden variety missing reference. */
 				strbuf_addf(err, "unable to resolve reference '%s'",
 					    refname);
+				ret = REF_TRANSACTION_ERROR_NONEXISTENT_REF;
 				goto error_return;
 			} else if (remove_dir_recursively(&ref_file,
 							  REMOVE_DIR_EMPTY_ONLY)) {
@@ -830,7 +834,7 @@ static int lock_raw_ref(struct files_ref_store *refs,
 					 * The error message set by
 					 * verify_refname_available() is OK.
 					 */
-					ret = TRANSACTION_NAME_CONFLICT;
+					ret = REF_TRANSACTION_ERROR_NAME_CONFLICT;
 					goto error_return;
 				} else {
 					/*
@@ -1517,10 +1521,11 @@ static int rename_tmp_log(struct files_ref_store *refs, const char *newrefname)
 	return ret;
 }
 
-static int write_ref_to_lockfile(struct files_ref_store *refs,
-				 struct ref_lock *lock,
-				 const struct object_id *oid,
-				 int skip_oid_verification, struct strbuf *err);
+static enum ref_transaction_error write_ref_to_lockfile(struct files_ref_store *refs,
+							struct ref_lock *lock,
+							const struct object_id *oid,
+							int skip_oid_verification,
+							struct strbuf *err);
 static int commit_ref_update(struct files_ref_store *refs,
 			     struct ref_lock *lock,
 			     const struct object_id *oid, const char *logmsg,
@@ -1926,10 +1931,11 @@ static int files_log_ref_write(struct files_ref_store *refs,
  * Write oid into the open lockfile, then close the lockfile. On
  * errors, rollback the lockfile, fill in *err and return -1.
  */
-static int write_ref_to_lockfile(struct files_ref_store *refs,
-				 struct ref_lock *lock,
-				 const struct object_id *oid,
-				 int skip_oid_verification, struct strbuf *err)
+static enum ref_transaction_error write_ref_to_lockfile(struct files_ref_store *refs,
+							struct ref_lock *lock,
+							const struct object_id *oid,
+							int skip_oid_verification,
+							struct strbuf *err)
 {
 	static char term = '\n';
 	struct object *o;
@@ -1943,7 +1949,7 @@ static int write_ref_to_lockfile(struct files_ref_store *refs,
 				"trying to write ref '%s' with nonexistent object %s",
 				lock->ref_name, oid_to_hex(oid));
 			unlock_ref(lock);
-			return -1;
+			return REF_TRANSACTION_ERROR_INVALID_NEW_VALUE;
 		}
 		if (o->type != OBJ_COMMIT && is_branch(lock->ref_name)) {
 			strbuf_addf(
@@ -1951,7 +1957,7 @@ static int write_ref_to_lockfile(struct files_ref_store *refs,
 				"trying to write non-commit object %s to branch '%s'",
 				oid_to_hex(oid), lock->ref_name);
 			unlock_ref(lock);
-			return -1;
+			return REF_TRANSACTION_ERROR_INVALID_NEW_VALUE;
 		}
 	}
 	fd = get_lock_file_fd(&lock->lk);
@@ -1962,7 +1968,7 @@ static int write_ref_to_lockfile(struct files_ref_store *refs,
 		strbuf_addf(err,
 			    "couldn't write '%s'", get_lock_file_path(&lock->lk));
 		unlock_ref(lock);
-		return -1;
+		return REF_TRANSACTION_ERROR_GENERIC;
 	}
 	return 0;
 }
@@ -2376,9 +2382,10 @@ static struct ref_iterator *files_reflog_iterator_begin(struct ref_store *ref_st
  * If update is a direct update of head_ref (the reference pointed to
  * by HEAD), then add an extra REF_LOG_ONLY update for HEAD.
  */
-static int split_head_update(struct ref_update *update,
-			     struct ref_transaction *transaction,
-			     const char *head_ref, struct strbuf *err)
+static enum ref_transaction_error split_head_update(struct ref_update *update,
+						    struct ref_transaction *transaction,
+						    const char *head_ref,
+						    struct strbuf *err)
 {
 	struct ref_update *new_update;
 
@@ -2402,7 +2409,7 @@ static int split_head_update(struct ref_update *update,
 			    "multiple updates for 'HEAD' (including one "
 			    "via its referent '%s') are not allowed",
 			    update->refname);
-		return TRANSACTION_NAME_CONFLICT;
+		return REF_TRANSACTION_ERROR_NAME_CONFLICT;
 	}
 
 	new_update = ref_transaction_add_update(
@@ -2430,10 +2437,10 @@ static int split_head_update(struct ref_update *update,
  * Note that the new update will itself be subject to splitting when
  * the iteration gets to it.
  */
-static int split_symref_update(struct ref_update *update,
-			       const char *referent,
-			       struct ref_transaction *transaction,
-			       struct strbuf *err)
+static enum ref_transaction_error split_symref_update(struct ref_update *update,
+						      const char *referent,
+						      struct ref_transaction *transaction,
+						      struct strbuf *err)
 {
 	struct ref_update *new_update;
 	unsigned int new_flags;
@@ -2450,7 +2457,7 @@ static int split_symref_update(struct ref_update *update,
 			    "multiple updates for '%s' (including one "
 			    "via symref '%s') are not allowed",
 			    referent, update->refname);
-		return TRANSACTION_NAME_CONFLICT;
+		return REF_TRANSACTION_ERROR_NAME_CONFLICT;
 	}
 
 	new_flags = update->flags;
@@ -2491,11 +2498,10 @@ static int split_symref_update(struct ref_update *update,
  * everything is OK, return 0; otherwise, write an error message to
  * err and return -1.
  */
-static int check_old_oid(struct ref_update *update, struct object_id *oid,
-			 struct strbuf *err)
+static enum ref_transaction_error check_old_oid(struct ref_update *update,
+						struct object_id *oid,
+						struct strbuf *err)
 {
-	int ret = TRANSACTION_GENERIC_ERROR;
-
 	if (!(update->flags & REF_HAVE_OLD) ||
 		   oideq(oid, &update->old_oid))
 		return 0;
@@ -2504,21 +2510,20 @@ static int check_old_oid(struct ref_update *update, struct object_id *oid,
 		strbuf_addf(err, "cannot lock ref '%s': "
 			    "reference already exists",
 			    ref_update_original_update_refname(update));
-		ret = TRANSACTION_CREATE_EXISTS;
-	}
-	else if (is_null_oid(oid))
+		return REF_TRANSACTION_ERROR_CREATE_EXISTS;
+	} else if (is_null_oid(oid)) {
 		strbuf_addf(err, "cannot lock ref '%s': "
 			    "reference is missing but expected %s",
 			    ref_update_original_update_refname(update),
 			    oid_to_hex(&update->old_oid));
-	else
-		strbuf_addf(err, "cannot lock ref '%s': "
-			    "is at %s but expected %s",
-			    ref_update_original_update_refname(update),
-			    oid_to_hex(oid),
-			    oid_to_hex(&update->old_oid));
+		return REF_TRANSACTION_ERROR_NONEXISTENT_REF;
+	}
 
-	return ret;
+	strbuf_addf(err, "cannot lock ref '%s': is at %s but expected %s",
+		    ref_update_original_update_refname(update), oid_to_hex(oid),
+		    oid_to_hex(&update->old_oid));
+
+	return REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE;
 }
 
 struct files_transaction_backend_data {
@@ -2540,17 +2545,17 @@ struct files_transaction_backend_data {
  * - If it is an update of head_ref, add a corresponding REF_LOG_ONLY
  *   update of HEAD.
  */
-static int lock_ref_for_update(struct files_ref_store *refs,
-			       struct ref_update *update,
-			       struct ref_transaction *transaction,
-			       const char *head_ref,
-			       struct string_list *refnames_to_check,
-			       struct strbuf *err)
+static enum ref_transaction_error lock_ref_for_update(struct files_ref_store *refs,
+						      struct ref_update *update,
+						      struct ref_transaction *transaction,
+						      const char *head_ref,
+						      struct string_list *refnames_to_check,
+						      struct strbuf *err)
 {
 	struct strbuf referent = STRBUF_INIT;
 	int mustexist = ref_update_expects_existing_old_ref(update);
 	struct files_transaction_backend_data *backend_data;
-	int ret = 0;
+	enum ref_transaction_error ret = 0;
 	struct ref_lock *lock;
 
 	files_assert_main_repository(refs, "lock_ref_for_update");
@@ -2602,22 +2607,17 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 					strbuf_addf(err, "cannot lock ref '%s': "
 						    "error reading reference",
 						    ref_update_original_update_refname(update));
-					ret = TRANSACTION_GENERIC_ERROR;
+					ret = REF_TRANSACTION_ERROR_GENERIC;
 					goto out;
 				}
 			}
 
-			if (update->old_target) {
-				if (ref_update_check_old_target(referent.buf, update, err)) {
-					ret = TRANSACTION_GENERIC_ERROR;
-					goto out;
-				}
-			} else {
+			if (update->old_target)
+				ret = ref_update_check_old_target(referent.buf, update, err);
+			else
 				ret = check_old_oid(update, &lock->old_oid, err);
-				if  (ret) {
-					goto out;
-				}
-			}
+			if (ret)
+				goto out;
 		} else {
 			/*
 			 * Create a new update for the reference this
@@ -2644,7 +2644,7 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 					   "but is a regular ref"),
 				    ref_update_original_update_refname(update),
 				    update->old_target);
-			ret = TRANSACTION_GENERIC_ERROR;
+			ret = REF_TRANSACTION_ERROR_EXPECTED_SYMREF;
 			goto out;
 		} else {
 			ret = check_old_oid(update, &lock->old_oid, err);
@@ -2668,14 +2668,14 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 
 	if (update->new_target && !(update->flags & REF_LOG_ONLY)) {
 		if (create_symref_lock(lock, update->new_target, err)) {
-			ret = TRANSACTION_GENERIC_ERROR;
+			ret = REF_TRANSACTION_ERROR_GENERIC;
 			goto out;
 		}
 
 		if (close_ref_gently(lock)) {
 			strbuf_addf(err, "couldn't close '%s.lock'",
 				    update->refname);
-			ret = TRANSACTION_GENERIC_ERROR;
+			ret = REF_TRANSACTION_ERROR_GENERIC;
 			goto out;
 		}
 
@@ -2693,25 +2693,27 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 			 * The reference already has the desired
 			 * value, so we don't need to write it.
 			 */
-		} else if (write_ref_to_lockfile(
-				   refs, lock, &update->new_oid,
-				   update->flags & REF_SKIP_OID_VERIFICATION,
-				   err)) {
-			char *write_err = strbuf_detach(err, NULL);
-
-			/*
-			 * The lock was freed upon failure of
-			 * write_ref_to_lockfile():
-			 */
-			update->backend_data = NULL;
-			strbuf_addf(err,
-				    "cannot update ref '%s': %s",
-				    update->refname, write_err);
-			free(write_err);
-			ret = TRANSACTION_GENERIC_ERROR;
-			goto out;
 		} else {
-			update->flags |= REF_NEEDS_COMMIT;
+			ret = write_ref_to_lockfile(
+				refs, lock, &update->new_oid,
+				update->flags & REF_SKIP_OID_VERIFICATION,
+				err);
+			if (ret) {
+				char *write_err = strbuf_detach(err, NULL);
+
+				/*
+				 * The lock was freed upon failure of
+				 * write_ref_to_lockfile():
+				 */
+				update->backend_data = NULL;
+				strbuf_addf(err,
+					    "cannot update ref '%s': %s",
+					    update->refname, write_err);
+				free(write_err);
+				goto out;
+			} else {
+				update->flags |= REF_NEEDS_COMMIT;
+			}
 		}
 	}
 	if (!(update->flags & REF_NEEDS_COMMIT)) {
@@ -2723,7 +2725,7 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 		if (close_ref_gently(lock)) {
 			strbuf_addf(err, "couldn't close '%s.lock'",
 				    update->refname);
-			ret = TRANSACTION_GENERIC_ERROR;
+			ret = REF_TRANSACTION_ERROR_GENERIC;
 			goto out;
 		}
 	}
@@ -2865,7 +2867,7 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 						refs->packed_ref_store,
 						transaction->flags, err);
 				if (!packed_transaction) {
-					ret = TRANSACTION_GENERIC_ERROR;
+					ret = REF_TRANSACTION_ERROR_GENERIC;
 					goto cleanup;
 				}
 
@@ -2897,13 +2899,13 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 	 */
 	if (refs_verify_refnames_available(refs->packed_ref_store, &refnames_to_check,
 					   &transaction->refnames, NULL, 0, err)) {
-		ret = TRANSACTION_NAME_CONFLICT;
+		ret = REF_TRANSACTION_ERROR_NAME_CONFLICT;
 		goto cleanup;
 	}
 
 	if (packed_transaction) {
 		if (packed_refs_lock(refs->packed_ref_store, 0, err)) {
-			ret = TRANSACTION_GENERIC_ERROR;
+			ret = REF_TRANSACTION_ERROR_GENERIC;
 			goto cleanup;
 		}
 		backend_data->packed_refs_locked = 1;
@@ -2934,7 +2936,7 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 			 */
 			backend_data->packed_transaction = NULL;
 			if (ref_transaction_abort(packed_transaction, err)) {
-				ret = TRANSACTION_GENERIC_ERROR;
+				ret = REF_TRANSACTION_ERROR_GENERIC;
 				goto cleanup;
 			}
 		}
@@ -3035,7 +3037,7 @@ static int files_transaction_finish_initial(struct files_ref_store *refs,
 	packed_transaction = ref_store_transaction_begin(refs->packed_ref_store,
 							 transaction->flags, err);
 	if (!packed_transaction) {
-		ret = TRANSACTION_GENERIC_ERROR;
+		ret = REF_TRANSACTION_ERROR_GENERIC;
 		goto cleanup;
 	}
 
@@ -3058,7 +3060,7 @@ static int files_transaction_finish_initial(struct files_ref_store *refs,
 			if (!loose_transaction) {
 				loose_transaction = ref_store_transaction_begin(&refs->base, 0, err);
 				if (!loose_transaction) {
-					ret = TRANSACTION_GENERIC_ERROR;
+					ret = REF_TRANSACTION_ERROR_GENERIC;
 					goto cleanup;
 				}
 			}
@@ -3083,19 +3085,19 @@ static int files_transaction_finish_initial(struct files_ref_store *refs,
 	}
 
 	if (packed_refs_lock(refs->packed_ref_store, 0, err)) {
-		ret = TRANSACTION_GENERIC_ERROR;
+		ret = REF_TRANSACTION_ERROR_GENERIC;
 		goto cleanup;
 	}
 
 	if (refs_verify_refnames_available(&refs->base, &refnames_to_check,
 					   &affected_refnames, NULL, 1, err)) {
 		packed_refs_unlock(refs->packed_ref_store);
-		ret = TRANSACTION_NAME_CONFLICT;
+		ret = REF_TRANSACTION_ERROR_NAME_CONFLICT;
 		goto cleanup;
 	}
 
 	if (ref_transaction_commit(packed_transaction, err)) {
-		ret = TRANSACTION_GENERIC_ERROR;
+		ret = REF_TRANSACTION_ERROR_GENERIC;
 		goto cleanup;
 	}
 	packed_refs_unlock(refs->packed_ref_store);
@@ -3103,7 +3105,7 @@ static int files_transaction_finish_initial(struct files_ref_store *refs,
 	if (loose_transaction) {
 		if (ref_transaction_prepare(loose_transaction, err) ||
 		    ref_transaction_commit(loose_transaction, err)) {
-			ret = TRANSACTION_GENERIC_ERROR;
+			ret = REF_TRANSACTION_ERROR_GENERIC;
 			goto cleanup;
 		}
 	}
@@ -3152,7 +3154,7 @@ static int files_transaction_finish(struct ref_store *ref_store,
 		if (update->flags & REF_NEEDS_COMMIT ||
 		    update->flags & REF_LOG_ONLY) {
 			if (parse_and_write_reflog(refs, update, lock, err)) {
-				ret = TRANSACTION_GENERIC_ERROR;
+				ret = REF_TRANSACTION_ERROR_GENERIC;
 				goto cleanup;
 			}
 		}
@@ -3171,7 +3173,7 @@ static int files_transaction_finish(struct ref_store *ref_store,
 				strbuf_addf(err, "couldn't set '%s'", lock->ref_name);
 				unlock_ref(lock);
 				update->backend_data = NULL;
-				ret = TRANSACTION_GENERIC_ERROR;
+				ret = REF_TRANSACTION_ERROR_GENERIC;
 				goto cleanup;
 			}
 		}
@@ -3227,7 +3229,7 @@ static int files_transaction_finish(struct ref_store *ref_store,
 				strbuf_reset(&sb);
 				files_ref_path(refs, &sb, lock->ref_name);
 				if (unlink_or_msg(sb.buf, err)) {
-					ret = TRANSACTION_GENERIC_ERROR;
+					ret = REF_TRANSACTION_ERROR_GENERIC;
 					goto cleanup;
 				}
 			}
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index 19220d2e99..d90bd815a3 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -1326,10 +1326,11 @@ static int packed_ref_store_remove_on_disk(struct ref_store *ref_store,
  * The packfile must be locked before calling this function and will
  * remain locked when it is done.
  */
-static int write_with_updates(struct packed_ref_store *refs,
-			      struct string_list *updates,
-			      struct strbuf *err)
+static enum ref_transaction_error write_with_updates(struct packed_ref_store *refs,
+						     struct string_list *updates,
+						     struct strbuf *err)
 {
+	enum ref_transaction_error ret = REF_TRANSACTION_ERROR_GENERIC;
 	struct ref_iterator *iter = NULL;
 	size_t i;
 	int ok;
@@ -1353,7 +1354,7 @@ static int write_with_updates(struct packed_ref_store *refs,
 		strbuf_addf(err, "unable to create file %s: %s",
 			    sb.buf, strerror(errno));
 		strbuf_release(&sb);
-		return -1;
+		return REF_TRANSACTION_ERROR_GENERIC;
 	}
 	strbuf_release(&sb);
 
@@ -1409,6 +1410,7 @@ static int write_with_updates(struct packed_ref_store *refs,
 					strbuf_addf(err, "cannot update ref '%s': "
 						    "reference already exists",
 						    update->refname);
+					ret = REF_TRANSACTION_ERROR_CREATE_EXISTS;
 					goto error;
 				} else if (!oideq(&update->old_oid, iter->oid)) {
 					strbuf_addf(err, "cannot update ref '%s': "
@@ -1416,6 +1418,7 @@ static int write_with_updates(struct packed_ref_store *refs,
 						    update->refname,
 						    oid_to_hex(iter->oid),
 						    oid_to_hex(&update->old_oid));
+					ret = REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE;
 					goto error;
 				}
 			}
@@ -1452,6 +1455,7 @@ static int write_with_updates(struct packed_ref_store *refs,
 					    "reference is missing but expected %s",
 					    update->refname,
 					    oid_to_hex(&update->old_oid));
+				ret = REF_TRANSACTION_ERROR_NONEXISTENT_REF;
 				goto error;
 			}
 		}
@@ -1509,7 +1513,7 @@ static int write_with_updates(struct packed_ref_store *refs,
 			    strerror(errno));
 		strbuf_release(&sb);
 		delete_tempfile(&refs->tempfile);
-		return -1;
+		return REF_TRANSACTION_ERROR_GENERIC;
 	}
 
 	return 0;
@@ -1521,7 +1525,7 @@ static int write_with_updates(struct packed_ref_store *refs,
 error:
 	ref_iterator_free(iter);
 	delete_tempfile(&refs->tempfile);
-	return -1;
+	return ret;
 }
 
 int is_packed_transaction_needed(struct ref_store *ref_store,
@@ -1654,7 +1658,7 @@ static int packed_transaction_prepare(struct ref_store *ref_store,
 			REF_STORE_READ | REF_STORE_WRITE | REF_STORE_ODB,
 			"ref_transaction_prepare");
 	struct packed_transaction_backend_data *data;
-	int ret = TRANSACTION_GENERIC_ERROR;
+	enum ref_transaction_error ret = REF_TRANSACTION_ERROR_GENERIC;
 
 	/*
 	 * Note that we *don't* skip transactions with zero updates,
@@ -1675,7 +1679,8 @@ static int packed_transaction_prepare(struct ref_store *ref_store,
 		data->own_lock = 1;
 	}
 
-	if (write_with_updates(refs, &transaction->refnames, err))
+	ret = write_with_updates(refs, &transaction->refnames, err);
+	if (ret)
 		goto failure;
 
 	transaction->state = REF_TRANSACTION_PREPARED;
@@ -1707,7 +1712,7 @@ static int packed_transaction_finish(struct ref_store *ref_store,
 			ref_store,
 			REF_STORE_READ | REF_STORE_WRITE | REF_STORE_ODB,
 			"ref_transaction_finish");
-	int ret = TRANSACTION_GENERIC_ERROR;
+	int ret = REF_TRANSACTION_ERROR_GENERIC;
 	char *packed_refs_path;
 
 	clear_snapshot(refs);
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 6d3770d0cc..3f1d19abd9 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -770,8 +770,9 @@ int ref_update_has_null_new_value(struct ref_update *update);
  * If everything is OK, return 0; otherwise, write an error message to
  * err and return -1.
  */
-int ref_update_check_old_target(const char *referent, struct ref_update *update,
-				struct strbuf *err);
+enum ref_transaction_error ref_update_check_old_target(const char *referent,
+						       struct ref_update *update,
+						       struct strbuf *err);
 
 /*
  * Check if the ref must exist, this means that the old_oid or
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 786df11a03..bd6b042103 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1069,20 +1069,20 @@ static int queue_transaction_update(struct reftable_ref_store *refs,
 	return 0;
 }
 
-static int prepare_single_update(struct reftable_ref_store *refs,
-				 struct reftable_transaction_data *tx_data,
-				 struct ref_transaction *transaction,
-				 struct reftable_backend *be,
-				 struct ref_update *u,
-				 struct string_list *refnames_to_check,
-				 unsigned int head_type,
-				 struct strbuf *head_referent,
-				 struct strbuf *referent,
-				 struct strbuf *err)
+static enum ref_transaction_error prepare_single_update(struct reftable_ref_store *refs,
+							struct reftable_transaction_data *tx_data,
+							struct ref_transaction *transaction,
+							struct reftable_backend *be,
+							struct ref_update *u,
+							struct string_list *refnames_to_check,
+							unsigned int head_type,
+							struct strbuf *head_referent,
+							struct strbuf *referent,
+							struct strbuf *err)
 {
+	enum ref_transaction_error ret = 0;
 	struct object_id current_oid = {0};
 	const char *rewritten_ref;
-	int ret = 0;
 
 	/*
 	 * There is no need to reload the respective backends here as
@@ -1093,7 +1093,7 @@ static int prepare_single_update(struct reftable_ref_store *refs,
 	 */
 	ret = backend_for(&be, refs, u->refname, &rewritten_ref, 0);
 	if (ret)
-		return ret;
+		return REF_TRANSACTION_ERROR_GENERIC;
 
 	/* Verify that the new object ID is valid. */
 	if ((u->flags & REF_HAVE_NEW) && !is_null_oid(&u->new_oid) &&
@@ -1104,13 +1104,13 @@ static int prepare_single_update(struct reftable_ref_store *refs,
 			strbuf_addf(err,
 				    _("trying to write ref '%s' with nonexistent object %s"),
 				    u->refname, oid_to_hex(&u->new_oid));
-			return -1;
+			return REF_TRANSACTION_ERROR_INVALID_NEW_VALUE;
 		}
 
 		if (o->type != OBJ_COMMIT && is_branch(u->refname)) {
 			strbuf_addf(err, _("trying to write non-commit object %s to branch '%s'"),
 				    oid_to_hex(&u->new_oid), u->refname);
-			return -1;
+			return REF_TRANSACTION_ERROR_INVALID_NEW_VALUE;
 		}
 	}
 
@@ -1134,7 +1134,7 @@ static int prepare_single_update(struct reftable_ref_store *refs,
 				    _("multiple updates for 'HEAD' (including one "
 				      "via its referent '%s') are not allowed"),
 				    u->refname);
-			return TRANSACTION_NAME_CONFLICT;
+			return REF_TRANSACTION_ERROR_NAME_CONFLICT;
 		}
 
 		ref_transaction_add_update(
@@ -1147,7 +1147,7 @@ static int prepare_single_update(struct reftable_ref_store *refs,
 	ret = reftable_backend_read_ref(be, rewritten_ref,
 					&current_oid, referent, &u->type);
 	if (ret < 0)
-		return ret;
+		return REF_TRANSACTION_ERROR_GENERIC;
 	if (ret > 0 && !ref_update_expects_existing_old_ref(u)) {
 		/*
 		 * The reference does not exist, and we either have no
@@ -1168,7 +1168,7 @@ static int prepare_single_update(struct reftable_ref_store *refs,
 			ret = queue_transaction_update(refs, tx_data, u,
 						       &current_oid, err);
 			if (ret)
-				return ret;
+				return REF_TRANSACTION_ERROR_GENERIC;
 		}
 
 		return 0;
@@ -1180,7 +1180,7 @@ static int prepare_single_update(struct reftable_ref_store *refs,
 
 				   "unable to resolve reference '%s'"),
 			    ref_update_original_update_refname(u), u->refname);
-		return -1;
+		return REF_TRANSACTION_ERROR_NONEXISTENT_REF;
 	}
 
 	if (u->type & REF_ISSYMREF) {
@@ -1196,7 +1196,7 @@ static int prepare_single_update(struct reftable_ref_store *refs,
 			if (u->flags & REF_HAVE_OLD && !resolved) {
 				strbuf_addf(err, _("cannot lock ref '%s': "
 						   "error reading reference"), u->refname);
-				return -1;
+				return REF_TRANSACTION_ERROR_GENERIC;
 			}
 		} else {
 			struct ref_update *new_update;
@@ -1211,7 +1211,7 @@ static int prepare_single_update(struct reftable_ref_store *refs,
 					    _("multiple updates for '%s' (including one "
 					      "via symref '%s') are not allowed"),
 					    referent->buf, u->refname);
-				return TRANSACTION_NAME_CONFLICT;
+				return REF_TRANSACTION_ERROR_NAME_CONFLICT;
 			}
 
 			/*
@@ -1255,31 +1255,32 @@ static int prepare_single_update(struct reftable_ref_store *refs,
 					   "but is a regular ref"),
 				    ref_update_original_update_refname(u),
 				    u->old_target);
-			return -1;
+			return REF_TRANSACTION_ERROR_EXPECTED_SYMREF;
 		}
 
-		if (ref_update_check_old_target(referent->buf, u, err)) {
-			return -1;
-		}
+		ret = ref_update_check_old_target(referent->buf, u, err);
+		if (ret)
+			return ret;
 	} else if ((u->flags & REF_HAVE_OLD) && !oideq(&current_oid, &u->old_oid)) {
 		if (is_null_oid(&u->old_oid)) {
 			strbuf_addf(err, _("cannot lock ref '%s': "
 					   "reference already exists"),
 				    ref_update_original_update_refname(u));
-			return TRANSACTION_CREATE_EXISTS;
-		}
-		else if (is_null_oid(&current_oid))
+			return REF_TRANSACTION_ERROR_CREATE_EXISTS;
+		} else if (is_null_oid(&current_oid)) {
 			strbuf_addf(err, _("cannot lock ref '%s': "
 					   "reference is missing but expected %s"),
 				    ref_update_original_update_refname(u),
 				    oid_to_hex(&u->old_oid));
-		else
+			return REF_TRANSACTION_ERROR_NONEXISTENT_REF;
+		} else {
 			strbuf_addf(err, _("cannot lock ref '%s': "
 					   "is at %s but expected %s"),
 				    ref_update_original_update_refname(u),
 				    oid_to_hex(&current_oid),
 				    oid_to_hex(&u->old_oid));
-		return TRANSACTION_NAME_CONFLICT;
+			return REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE;
+		}
 	}
 
 	/*
@@ -1296,8 +1297,8 @@ static int prepare_single_update(struct reftable_ref_store *refs,
 	if ((u->type & REF_ISSYMREF) ||
 	    (u->flags & REF_LOG_ONLY) ||
 	    (u->flags & REF_HAVE_NEW && !oideq(&current_oid, &u->new_oid)))
-		return queue_transaction_update(refs, tx_data, u,
-					       &current_oid, err);
+		if (queue_transaction_update(refs, tx_data, u, &current_oid, err))
+			return REF_TRANSACTION_ERROR_GENERIC;
 
 	return 0;
 }
@@ -1385,7 +1386,6 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 	transaction->state = REF_TRANSACTION_PREPARED;
 
 done:
-	assert(ret != REFTABLE_API_ERROR);
 	if (ret < 0) {
 		free_transaction_data(tx_data);
 		transaction->state = REF_TRANSACTION_CLOSED;
-- 
2.48.1
Patrick Steinhardt· Mar 20, 2025, 20:26 UTC · re: Karthik Nayak · lore

Re: [PATCH v4 5/8] refs: introduce enum-based transaction error types

On Thu, Mar 20, 2025 at 12:44:00PM +0100, Karthik Nayak wrote:
Show 31 quoted lines
> diff --git a/refs.h b/refs.h
> index 240e2d8537..dcd83e81e2 100644
> --- a/refs.h
> +++ b/refs.h
> @@ -16,6 +16,29 @@ struct worktree;
>  enum ref_storage_format ref_storage_format_by_name(const char *name);
>  const char *ref_storage_format_to_name(enum ref_storage_format ref_storage_format);
>  
> +/*
> + * enum ref_transaction_error represents the following return codes:
> + * REF_TRANSACTION_ERROR_GENERIC error_code: default error code.
> + * REF_TRANSACTION_ERROR_NAME_CONFLICT error_code: ref name conflict like A vs A/B.
> + * REF_TRANSACTION_ERROR_CREATE_EXISTS error_code: ref to be created already exists.
> + * REF_TRANSACTION_ERROR_NONEXISTENT_REF error_code: ref expected but doesn't exist.
> + * REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE error_code: provided old_oid or old_target of
> + * reference doesn't match actual.
> + * REF_TRANSACTION_ERROR_INVALID_NEW_VALUE error_code: provided new_oid or new_target is
> + * invalid.
> + * REF_TRANSACTION_ERROR_EXPECTED_SYMREF error_code: expected ref to be symref, but is a
> + * regular ref.
> + */
> +enum ref_transaction_error {
> +	REF_TRANSACTION_ERROR_GENERIC = -1,
> +	REF_TRANSACTION_ERROR_NAME_CONFLICT = -2,
> +	REF_TRANSACTION_ERROR_CREATE_EXISTS = -3,
> +	REF_TRANSACTION_ERROR_NONEXISTENT_REF = -4,
> +	REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE = -5,
> +	REF_TRANSACTION_ERROR_INVALID_NEW_VALUE = -6,
> +	REF_TRANSACTION_ERROR_EXPECTED_SYMREF = -7,
> +};
> +

Tiny nit: I think it's generally preferable to document each specific right next to its definition.

Patrick
Karthik Nayak· Mar 24, 2025, 14:50 UTC · re: Patrick Steinhardt · lore

Re: [PATCH v4 5/8] refs: introduce enum-based transaction error types

Patrick Steinhardt <ps@pks.im> writes:
Show 36 quoted lines
> On Thu, Mar 20, 2025 at 12:44:00PM +0100, Karthik Nayak wrote:
>> diff --git a/refs.h b/refs.h
>> index 240e2d8537..dcd83e81e2 100644
>> --- a/refs.h
>> +++ b/refs.h
>> @@ -16,6 +16,29 @@ struct worktree;
>>  enum ref_storage_format ref_storage_format_by_name(const char *name);
>>  const char *ref_storage_format_to_name(enum ref_storage_format ref_storage_format);
>>
>> +/*
>> + * enum ref_transaction_error represents the following return codes:
>> + * REF_TRANSACTION_ERROR_GENERIC error_code: default error code.
>> + * REF_TRANSACTION_ERROR_NAME_CONFLICT error_code: ref name conflict like A vs A/B.
>> + * REF_TRANSACTION_ERROR_CREATE_EXISTS error_code: ref to be created already exists.
>> + * REF_TRANSACTION_ERROR_NONEXISTENT_REF error_code: ref expected but doesn't exist.
>> + * REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE error_code: provided old_oid or old_target of
>> + * reference doesn't match actual.
>> + * REF_TRANSACTION_ERROR_INVALID_NEW_VALUE error_code: provided new_oid or new_target is
>> + * invalid.
>> + * REF_TRANSACTION_ERROR_EXPECTED_SYMREF error_code: expected ref to be symref, but is a
>> + * regular ref.
>> + */
>> +enum ref_transaction_error {
>> +	REF_TRANSACTION_ERROR_GENERIC = -1,
>> +	REF_TRANSACTION_ERROR_NAME_CONFLICT = -2,
>> +	REF_TRANSACTION_ERROR_CREATE_EXISTS = -3,
>> +	REF_TRANSACTION_ERROR_NONEXISTENT_REF = -4,
>> +	REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE = -5,
>> +	REF_TRANSACTION_ERROR_INVALID_NEW_VALUE = -6,
>> +	REF_TRANSACTION_ERROR_EXPECTED_SYMREF = -7,
>> +};
>> +
>
> Tiny nit: I think it's generally preferable to document each specific
> right next to its definition.
>

Idk about this, I based it off on `enum bisect_error` which is similar, but I also see the same in `enum scld_error`.

I'm okay to change this though, perhaps makes sense to document the preferred style however.

> Patrick
Patrick Steinhardt· Mar 25, 2025, 12:31 UTC · re: Karthik Nayak · lore

Re: [PATCH v4 5/8] refs: introduce enum-based transaction error types

On Mon, Mar 24, 2025 at 02:50:56PM +0000, Karthik Nayak wrote:
Show 44 quoted lines
> Patrick Steinhardt <ps@pks.im> writes:
> 
> > On Thu, Mar 20, 2025 at 12:44:00PM +0100, Karthik Nayak wrote:
> >> diff --git a/refs.h b/refs.h
> >> index 240e2d8537..dcd83e81e2 100644
> >> --- a/refs.h
> >> +++ b/refs.h
> >> @@ -16,6 +16,29 @@ struct worktree;
> >>  enum ref_storage_format ref_storage_format_by_name(const char *name);
> >>  const char *ref_storage_format_to_name(enum ref_storage_format ref_storage_format);
> >>
> >> +/*
> >> + * enum ref_transaction_error represents the following return codes:
> >> + * REF_TRANSACTION_ERROR_GENERIC error_code: default error code.
> >> + * REF_TRANSACTION_ERROR_NAME_CONFLICT error_code: ref name conflict like A vs A/B.
> >> + * REF_TRANSACTION_ERROR_CREATE_EXISTS error_code: ref to be created already exists.
> >> + * REF_TRANSACTION_ERROR_NONEXISTENT_REF error_code: ref expected but doesn't exist.
> >> + * REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE error_code: provided old_oid or old_target of
> >> + * reference doesn't match actual.
> >> + * REF_TRANSACTION_ERROR_INVALID_NEW_VALUE error_code: provided new_oid or new_target is
> >> + * invalid.
> >> + * REF_TRANSACTION_ERROR_EXPECTED_SYMREF error_code: expected ref to be symref, but is a
> >> + * regular ref.
> >> + */
> >> +enum ref_transaction_error {
> >> +	REF_TRANSACTION_ERROR_GENERIC = -1,
> >> +	REF_TRANSACTION_ERROR_NAME_CONFLICT = -2,
> >> +	REF_TRANSACTION_ERROR_CREATE_EXISTS = -3,
> >> +	REF_TRANSACTION_ERROR_NONEXISTENT_REF = -4,
> >> +	REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE = -5,
> >> +	REF_TRANSACTION_ERROR_INVALID_NEW_VALUE = -6,
> >> +	REF_TRANSACTION_ERROR_EXPECTED_SYMREF = -7,
> >> +};
> >> +
> >
> > Tiny nit: I think it's generally preferable to document each specific
> > right next to its definition.
> >
> 
> Idk about this, I based it off on `enum bisect_error` which is similar,
> but I also see the same in `enum scld_error`.
> 
> I'm okay to change this though, perhaps makes sense to document the
> preferred style however.

Probably would make sense, yes. The argument for why it's preferable to do this inline is that it's harder for the list to grow stale. It's trivial to see when a comment needs to be removed/updated.

Patrick
Karthik Nayak· Mar 20, 2025, 11:44 UTC · re: Karthik Nayak · lore

[PATCH v4 7/8] refs: support rejection in batch updates during F/D checks

The `refs_verify_refnames_available()` is used to batch check refnames for F/D conflicts. While this is the more performant alternative than its individual version, it does not provide rejection capabilities on a single update level. For batched updates, this would mean a rejection of the entire transaction whenever one reference has a F/D conflict.

Modify the function to call `ref_transaction_maybe_set_rejected()` to check if a single update can be rejected. Since this function is only internally used within 'refs/' and we want to pass in a `struct ref_transaction *` as a variable. We also move and mark `refs_verify_refnames_available()` to 'refs-internal.h' to be an internal function.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 refs.c                  | 28 +++++++++++++++++++++++++++-
 refs.h                  | 12 ------------
 refs/files-backend.c    | 27 ++++++++++++++++++---------
 refs/refs-internal.h    | 16 ++++++++++++++++
 refs/reftable-backend.c | 11 ++++++++---
 5 files changed, 69 insertions(+), 25 deletions(-)
Show changes to 5 files +69 −25

refs.c, refs.h, refs/files-backend.c, refs/refs-internal.h, refs/reftable-backend.c

diff --git a/refs.c b/refs.c
index b34ec198f5..f719046f47 100644
--- a/refs.c
+++ b/refs.c
@@ -2540,6 +2540,7 @@ enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs
 					  const struct string_list *refnames,
 					  const struct string_list *extras,
 					  const struct string_list *skip,
+					  struct ref_transaction *transaction,
 					  unsigned int initial_transaction,
 					  struct strbuf *err)
 {
@@ -2560,6 +2561,7 @@ enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs
 	strset_init(&dirnames);
 
 	for_each_string_list_item(item, refnames) {
+		const size_t *update_idx = (size_t *)item->util;
 		const char *refname = item->string;
 		const char *extra_refname;
 		struct object_id oid;
@@ -2599,12 +2601,26 @@ enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs
 			if (!initial_transaction &&
 			    !refs_read_raw_ref(refs, dirname.buf, &oid, &referent,
 					       &type, &ignore_errno)) {
+				if (transaction && ref_transaction_maybe_set_rejected(
+					    transaction, *update_idx,
+					    REF_TRANSACTION_ERROR_NAME_CONFLICT)) {
+					strset_remove(&dirnames, dirname.buf);
+					continue;
+				}
+
 				strbuf_addf(err, _("'%s' exists; cannot create '%s'"),
 					    dirname.buf, refname);
 				goto cleanup;
 			}
 
 			if (extras && string_list_has_string(extras, dirname.buf)) {
+				if (transaction && ref_transaction_maybe_set_rejected(
+					    transaction, *update_idx,
+					    REF_TRANSACTION_ERROR_NAME_CONFLICT)) {
+					strset_remove(&dirnames, dirname.buf);
+					continue;
+				}
+
 				strbuf_addf(err, _("cannot process '%s' and '%s' at the same time"),
 					    refname, dirname.buf);
 				goto cleanup;
@@ -2637,6 +2653,11 @@ enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs
 				    string_list_has_string(skip, iter->refname))
 					continue;
 
+				if (transaction && ref_transaction_maybe_set_rejected(
+					    transaction, *update_idx,
+					    REF_TRANSACTION_ERROR_NAME_CONFLICT))
+					continue;
+
 				strbuf_addf(err, _("'%s' exists; cannot create '%s'"),
 					    iter->refname, refname);
 				goto cleanup;
@@ -2648,6 +2669,11 @@ enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs
 
 		extra_refname = find_descendant_ref(dirname.buf, extras, skip);
 		if (extra_refname) {
+			if (transaction && ref_transaction_maybe_set_rejected(
+				    transaction, *update_idx,
+				    REF_TRANSACTION_ERROR_NAME_CONFLICT))
+				continue;
+
 			strbuf_addf(err, _("cannot process '%s' and '%s' at the same time"),
 				    refname, extra_refname);
 			goto cleanup;
@@ -2679,7 +2705,7 @@ enum ref_transaction_error refs_verify_refname_available(
 	};
 
 	return refs_verify_refnames_available(refs, &refnames, extras, skip,
-					      initial_transaction, err);
+					      NULL, initial_transaction, err);
 }
 
 struct do_for_each_reflog_help {
diff --git a/refs.h b/refs.h
index 591b703d59..1e7ab2532f 100644
--- a/refs.h
+++ b/refs.h
@@ -147,18 +147,6 @@ enum ref_transaction_error refs_verify_refname_available(struct ref_store *refs,
 						 unsigned int initial_transaction,
 						 struct strbuf *err);
 
-/*
- * Same as `refs_verify_refname_available()`, but checking for a list of
- * refnames instead of only a single item. This is more efficient in the case
- * where one needs to check multiple refnames.
- */
-enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs,
-					  const struct string_list *refnames,
-					  const struct string_list *extras,
-					  const struct string_list *skip,
-					  unsigned int initial_transaction,
-					  struct strbuf *err);
-
 int refs_ref_exists(struct ref_store *refs, const char *refname);
 
 int should_autocreate_reflog(enum log_refs_config log_all_ref_updates,
diff --git a/refs/files-backend.c b/refs/files-backend.c
index be758ffff5..1d50d4013c 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -677,16 +677,18 @@ static void unlock_ref(struct ref_lock *lock)
  * - Generate informative error messages in the case of failure
  */
 static enum ref_transaction_error lock_raw_ref(struct files_ref_store *refs,
-					       const char *refname,
+					       struct ref_update *update,
+					       size_t update_idx,
 					       int mustexist,
 					       struct string_list *refnames_to_check,
 					       const struct string_list *extras,
 					       struct ref_lock **lock_p,
 					       struct strbuf *referent,
-					       unsigned int *type,
 					       struct strbuf *err)
 {
 	enum ref_transaction_error ret = REF_TRANSACTION_ERROR_GENERIC;
+	const char *refname = update->refname;
+	unsigned int *type = &update->type;
 	struct ref_lock *lock;
 	struct strbuf ref_file = STRBUF_INIT;
 	int attempts_remaining = 3;
@@ -785,6 +787,8 @@ static enum ref_transaction_error lock_raw_ref(struct files_ref_store *refs,
 
 	if (files_read_raw_ref(&refs->base, refname, &lock->old_oid, referent,
 			       type, &failure_errno)) {
+		struct string_list_item *item;
+
 		if (failure_errno == ENOENT) {
 			if (mustexist) {
 				/* Garden variety missing reference. */
@@ -864,7 +868,9 @@ static enum ref_transaction_error lock_raw_ref(struct files_ref_store *refs,
 		 * make sure there is no existing packed ref that conflicts
 		 * with refname. This check is deferred so that we can batch it.
 		 */
-		string_list_append(refnames_to_check, refname);
+		item = string_list_append(refnames_to_check, refname);
+		item->util = xmalloc(sizeof(update_idx));
+		memcpy(item->util, &update_idx, sizeof(update_idx));
 	}
 
 	ret = 0;
@@ -2547,6 +2553,7 @@ struct files_transaction_backend_data {
  */
 static enum ref_transaction_error lock_ref_for_update(struct files_ref_store *refs,
 						      struct ref_update *update,
+						      size_t update_idx,
 						      struct ref_transaction *transaction,
 						      const char *head_ref,
 						      struct string_list *refnames_to_check,
@@ -2575,9 +2582,9 @@ static enum ref_transaction_error lock_ref_for_update(struct files_ref_store *re
 	if (lock) {
 		lock->count++;
 	} else {
-		ret = lock_raw_ref(refs, update->refname, mustexist,
+		ret = lock_raw_ref(refs, update, update_idx, mustexist,
 				   refnames_to_check, &transaction->refnames,
-				   &lock, &referent, &update->type, err);
+				   &lock, &referent, err);
 		if (ret) {
 			char *reason;
 
@@ -2849,7 +2856,7 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 	for (i = 0; i < transaction->nr; i++) {
 		struct ref_update *update = transaction->updates[i];
 
-		ret = lock_ref_for_update(refs, update, transaction,
+		ret = lock_ref_for_update(refs, update, i, transaction,
 					  head_ref, &refnames_to_check,
 					  err);
 		if (ret) {
@@ -2905,7 +2912,8 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 	 * So instead, we accept the race for now.
 	 */
 	if (refs_verify_refnames_available(refs->packed_ref_store, &refnames_to_check,
-					   &transaction->refnames, NULL, 0, err)) {
+					   &transaction->refnames, NULL, transaction,
+					   0, err)) {
 		ret = REF_TRANSACTION_ERROR_NAME_CONFLICT;
 		goto cleanup;
 	}
@@ -2951,7 +2959,7 @@ static int files_transaction_prepare(struct ref_store *ref_store,
 
 cleanup:
 	free(head_ref);
-	string_list_clear(&refnames_to_check, 0);
+	string_list_clear(&refnames_to_check, 1);
 
 	if (ret)
 		files_transaction_cleanup(refs, transaction);
@@ -3097,7 +3105,8 @@ static int files_transaction_finish_initial(struct files_ref_store *refs,
 	}
 
 	if (refs_verify_refnames_available(&refs->base, &refnames_to_check,
-					   &affected_refnames, NULL, 1, err)) {
+					   &affected_refnames, NULL, transaction,
+					   1, err)) {
 		packed_refs_unlock(refs->packed_ref_store);
 		ret = REF_TRANSACTION_ERROR_NAME_CONFLICT;
 		goto cleanup;
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 73a5379b73..f868870851 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -806,4 +806,20 @@ enum ref_transaction_error ref_update_check_old_target(const char *referent,
  */
 int ref_update_expects_existing_old_ref(struct ref_update *update);
 
+/*
+ * Same as `refs_verify_refname_available()`, but checking for a list of
+ * refnames instead of only a single item. This is more efficient in the case
+ * where one needs to check multiple refnames.
+ *
+ * If using batched updates, then individual updates are marked rejected,
+ * reference backends are then in charge of not committing those updates.
+ */
+enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs,
+					  const struct string_list *refnames,
+					  const struct string_list *extras,
+					  const struct string_list *skip,
+					  struct ref_transaction *transaction,
+					  unsigned int initial_transaction,
+					  struct strbuf *err);
+
 #endif /* REFS_REFS_INTERNAL_H */
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index ed65225763..f5429c918b 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1074,6 +1074,7 @@ static enum ref_transaction_error prepare_single_update(struct reftable_ref_stor
 							struct ref_transaction *transaction,
 							struct reftable_backend *be,
 							struct ref_update *u,
+							size_t update_idx,
 							struct string_list *refnames_to_check,
 							unsigned int head_type,
 							struct strbuf *head_referent,
@@ -1149,6 +1150,7 @@ static enum ref_transaction_error prepare_single_update(struct reftable_ref_stor
 	if (ret < 0)
 		return REF_TRANSACTION_ERROR_GENERIC;
 	if (ret > 0 && !ref_update_expects_existing_old_ref(u)) {
+		struct string_list_item *item;
 		/*
 		 * The reference does not exist, and we either have no
 		 * old object ID or expect the reference to not exist.
@@ -1158,7 +1160,9 @@ static enum ref_transaction_error prepare_single_update(struct reftable_ref_stor
 		 * can output a proper error message instead of failing
 		 * at a later point.
 		 */
-		string_list_append(refnames_to_check, u->refname);
+		item = string_list_append(refnames_to_check, u->refname);
+		item->util = xmalloc(sizeof(update_idx));
+		memcpy(item->util, &update_idx, sizeof(update_idx));
 
 		/*
 		 * There is no need to write the reference deletion
@@ -1368,7 +1372,7 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 
 	for (i = 0; i < transaction->nr; i++) {
 		ret = prepare_single_update(refs, tx_data, transaction, be,
-					    transaction->updates[i],
+					    transaction->updates[i], i,
 					    &refnames_to_check, head_type,
 					    &head_referent, &referent, err);
 		if (ret) {
@@ -1384,6 +1388,7 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 
 	ret = refs_verify_refnames_available(ref_store, &refnames_to_check,
 					     &transaction->refnames, NULL,
+					     transaction,
 					     transaction->flags & REF_TRANSACTION_FLAG_INITIAL,
 					     err);
 	if (ret < 0)
@@ -1402,7 +1407,7 @@ static int reftable_be_transaction_prepare(struct ref_store *ref_store,
 	}
 	strbuf_release(&referent);
 	strbuf_release(&head_referent);
-	string_list_clear(&refnames_to_check, 0);
+	string_list_clear(&refnames_to_check, 1);
 
 	return ret;
 }
-- 
2.48.1
Patrick Steinhardt· Mar 24, 2025, 13:08 UTC · re: Karthik Nayak · lore

Re: [PATCH v4 7/8] refs: support rejection in batch updates during F/D checks

On Thu, Mar 20, 2025 at 12:44:02PM +0100, Karthik Nayak wrote:
Show 23 quoted lines
> diff --git a/refs.c b/refs.c
> index b34ec198f5..f719046f47 100644
> --- a/refs.c
> +++ b/refs.c
> @@ -2540,6 +2540,7 @@ enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs
>  					  const struct string_list *refnames,
>  					  const struct string_list *extras,
>  					  const struct string_list *skip,
> +					  struct ref_transaction *transaction,
>  					  unsigned int initial_transaction,
>  					  struct strbuf *err)
>  {
> @@ -2599,12 +2601,26 @@ enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs
>  			if (!initial_transaction &&
>  			    !refs_read_raw_ref(refs, dirname.buf, &oid, &referent,
>  					       &type, &ignore_errno)) {
> +				if (transaction && ref_transaction_maybe_set_rejected(
> +					    transaction, *update_idx,
> +					    REF_TRANSACTION_ERROR_NAME_CONFLICT)) {
> +					strset_remove(&dirnames, dirname.buf);
> +					continue;
> +				}
> +

Okay. We have to remove the dirname from `dirnames` again so that the next reference that creates a reference in the same directory would also be marked as conflicting. It does have the consequence that we now have to read the dirname N times again, where N is the number of refs that are created below that directory.

We could probably improve this by using another map that contains the conflicting names, right?

Show 15 quoted lines
> diff --git a/refs/files-backend.c b/refs/files-backend.c
> index be758ffff5..1d50d4013c 100644
> --- a/refs/files-backend.c
> +++ b/refs/files-backend.c
> @@ -864,7 +868,9 @@ static enum ref_transaction_error lock_raw_ref(struct files_ref_store *refs,
>  		 * make sure there is no existing packed ref that conflicts
>  		 * with refname. This check is deferred so that we can batch it.
>  		 */
> -		string_list_append(refnames_to_check, refname);
> +		item = string_list_append(refnames_to_check, refname);
> +		item->util = xmalloc(sizeof(update_idx));
> +		memcpy(item->util, &update_idx, sizeof(update_idx));
>  	}
>  
>  	ret = 0;

Hm, so we have to allocate the `util` field now to store the update index, which is a bit unfortunate because all of this is part of the hot loop. We cannot store a direct pointer though because the array of updates may be reallocated, which would invalidate any pointers pointing into the array.

I was wondering whether we could abuse an `uintptr_t` and use it to store the update index as a pointer. It does feel somewhat dirty though.

Patrick
Karthik Nayak· Mar 24, 2025, 17:48 UTC · re: Patrick Steinhardt · lore

Re: [PATCH v4 7/8] refs: support rejection in batch updates during F/D checks

Patrick Steinhardt <ps@pks.im> writes:
Show 34 quoted lines
> On Thu, Mar 20, 2025 at 12:44:02PM +0100, Karthik Nayak wrote:
>> diff --git a/refs.c b/refs.c
>> index b34ec198f5..f719046f47 100644
>> --- a/refs.c
>> +++ b/refs.c
>> @@ -2540,6 +2540,7 @@ enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs
>>  					  const struct string_list *refnames,
>>  					  const struct string_list *extras,
>>  					  const struct string_list *skip,
>> +					  struct ref_transaction *transaction,
>>  					  unsigned int initial_transaction,
>>  					  struct strbuf *err)
>>  {
>> @@ -2599,12 +2601,26 @@ enum ref_transaction_error refs_verify_refnames_available(struct ref_store *refs
>>  			if (!initial_transaction &&
>>  			    !refs_read_raw_ref(refs, dirname.buf, &oid, &referent,
>>  					       &type, &ignore_errno)) {
>> +				if (transaction && ref_transaction_maybe_set_rejected(
>> +					    transaction, *update_idx,
>> +					    REF_TRANSACTION_ERROR_NAME_CONFLICT)) {
>> +					strset_remove(&dirnames, dirname.buf);
>> +					continue;
>> +				}
>> +
>
> Okay. We have to remove the dirname from `dirnames` again so that the
> next reference that creates a reference in the same directory would also
> be marked as conflicting. It does have the consequence that we now have
> to read the dirname N times again, where N is the number of refs that
> are created below that directory.
>
> We could probably improve this by using another map that contains the
> conflicting names, right?
>
Yes that's definitely possible, I will go ahead and add it!
Show 22 quoted lines
>> diff --git a/refs/files-backend.c b/refs/files-backend.c
>> index be758ffff5..1d50d4013c 100644
>> --- a/refs/files-backend.c
>> +++ b/refs/files-backend.c
>> @@ -864,7 +868,9 @@ static enum ref_transaction_error lock_raw_ref(struct files_ref_store *refs,
>>  		 * make sure there is no existing packed ref that conflicts
>>  		 * with refname. This check is deferred so that we can batch it.
>>  		 */
>> -		string_list_append(refnames_to_check, refname);
>> +		item = string_list_append(refnames_to_check, refname);
>> +		item->util = xmalloc(sizeof(update_idx));
>> +		memcpy(item->util, &update_idx, sizeof(update_idx));
>>  	}
>>
>>  	ret = 0;
>
> Hm, so we have to allocate the `util` field now to store the update
> index, which is a bit unfortunate because all of this is part of the hot
> loop. We cannot store a direct pointer though because the array of
> updates may be reallocated, which would invalidate any pointers pointing
> into the array.
>
Yes, your inference is on point.
> I was wondering whether we could abuse an `uintptr_t` and use it to
> store the update index as a pointer. It does feel somewhat dirty though.
>

We can do something like this, it would be _clever_ but does feel very hacky.

I did so some benchmarking here
Benchmark 1: update-ref: create many refs (refformat = files, refcount
= 100000, revision = master)
  Time (mean ± σ):      7.396 s ±  0.175 s    [User: 0.962 s, System: 6.312 s]
  Range (min … max):    7.145 s …  7.688 s    10 runs
Benchmark 2: update-ref: create many refs (refformat = files, refcount
= 100000, revision = b4/245-partially-atomic-ref-updates)
  Time (mean ± σ):      7.514 s ±  0.144 s    [User: 0.919 s, System: 6.438 s]
  Range (min … max):    7.297 s …  7.750 s    10 runs
Summary
  update-ref: create many refs (refformat = files, refcount = 100000,
revision = master) ran
    1.02 ± 0.03 times faster than update-ref: create many refs
(refformat = files, refcount = 100000, revision =
b4/245-partially-atomic-ref-updates)

Overall the perf degradation is very minimal. I also looked at the flamegraph to see if there is something. But most of the time seems to be spent in IO (reading refs and creating locks).

So I think we should be ok here, wdyt?
> Patrick
Patrick Steinhardt· Mar 25, 2025, 12:31 UTC · re: Karthik Nayak · lore

Re: [PATCH v4 7/8] refs: support rejection in batch updates during F/D checks

On Mon, Mar 24, 2025 at 05:48:32PM +0000, Karthik Nayak wrote:
Show 58 quoted lines
> Patrick Steinhardt <ps@pks.im> writes:
> > On Thu, Mar 20, 2025 at 12:44:02PM +0100, Karthik Nayak wrote:
> >> diff --git a/refs/files-backend.c b/refs/files-backend.c
> >> index be758ffff5..1d50d4013c 100644
> >> --- a/refs/files-backend.c
> >> +++ b/refs/files-backend.c
> >> @@ -864,7 +868,9 @@ static enum ref_transaction_error lock_raw_ref(struct files_ref_store *refs,
> >>  		 * make sure there is no existing packed ref that conflicts
> >>  		 * with refname. This check is deferred so that we can batch it.
> >>  		 */
> >> -		string_list_append(refnames_to_check, refname);
> >> +		item = string_list_append(refnames_to_check, refname);
> >> +		item->util = xmalloc(sizeof(update_idx));
> >> +		memcpy(item->util, &update_idx, sizeof(update_idx));
> >>  	}
> >>
> >>  	ret = 0;
> >
> > Hm, so we have to allocate the `util` field now to store the update
> > index, which is a bit unfortunate because all of this is part of the hot
> > loop. We cannot store a direct pointer though because the array of
> > updates may be reallocated, which would invalidate any pointers pointing
> > into the array.
> >
> 
> Yes, your inference is on point.
> 
> > I was wondering whether we could abuse an `uintptr_t` and use it to
> > store the update index as a pointer. It does feel somewhat dirty though.
> >
> 
> We can do something like this, it would be _clever_ but does feel very
> hacky.
> 
> I did so some benchmarking here
> 
> Benchmark 1: update-ref: create many refs (refformat = files, refcount
> = 100000, revision = master)
>   Time (mean ± σ):      7.396 s ±  0.175 s    [User: 0.962 s, System: 6.312 s]
>   Range (min … max):    7.145 s …  7.688 s    10 runs
> 
> Benchmark 2: update-ref: create many refs (refformat = files, refcount
> = 100000, revision = b4/245-partially-atomic-ref-updates)
>   Time (mean ± σ):      7.514 s ±  0.144 s    [User: 0.919 s, System: 6.438 s]
>   Range (min … max):    7.297 s …  7.750 s    10 runs
> 
> Summary
>   update-ref: create many refs (refformat = files, refcount = 100000,
> revision = master) ran
>     1.02 ± 0.03 times faster than update-ref: create many refs
> (refformat = files, refcount = 100000, revision =
> b4/245-partially-atomic-ref-updates)
> 
> Overall the perf degradation is very minimal. I also looked at the
> flamegraph to see if there is something. But most of the time seems to
> be spent in IO (reading refs and creating locks).
> 
> So I think we should be ok here, wdyt?

Okay. I'm not a huge fan of using the `->util` pointer like this, but I don't have a better idea either, and the performance regression seems acceptable. So let's roll with it until somebody has a better idea.

Thanks for doing the benchmark!
Patrick
Karthik Nayak· Mar 20, 2025, 11:44 UTC · re: Karthik Nayak · lore

[PATCH v4 8/8] update-ref: add --batch-updates flag for stdin mode

When updating multiple references through stdin, Git's update-ref command normally aborts the entire transaction if any single update fails. This atomic behavior prevents partial updates. Introduce a new batch update system, where the updates the performed together similar but individual updates are allowed to fail.

Add a new `--batch-updates` flag that allows the transaction to continue even when individual reference updates fail. This flag can only be used in `--stdin` mode and builds upon the batch update support added to the refs subsystem in the previous commits. When enabled, failed updates are reported in the following format:

  rejected SP (<old-oid> | <old-target>) SP (<new-oid> | <new-target>) SP <rejection-reason> LF

Update the documentation to reflect this change and also tests to cover different scenarios where an update could be rejected.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 Documentation/git-update-ref.adoc |  14 ++-
 builtin/update-ref.c              |  67 ++++++++++-
 t/t1400-update-ref.sh             | 233 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 306 insertions(+), 8 deletions(-)
Show changes to 3 files +306 −8

Documentation/git-update-ref.adoc, builtin/update-ref.c, t/t1400-update-ref.sh

diff --git a/Documentation/git-update-ref.adoc b/Documentation/git-update-ref.adoc
index 9e6935d38d..5be2c16776 100644
--- a/Documentation/git-update-ref.adoc
+++ b/Documentation/git-update-ref.adoc
@@ -7,8 +7,10 @@ git-update-ref - Update the object name stored in a ref safely
 
 SYNOPSIS
 --------
-[verse]
-'git update-ref' [-m <reason>] [--no-deref] (-d <ref> [<old-oid>] | [--create-reflog] <ref> <new-oid> [<old-oid>] | --stdin [-z])
+[synopsis]
+git update-ref [-m <reason>] [--no-deref] -d <ref> [<old-oid>]
+	       [-m <reason>] [--no-deref] [--create-reflog] <ref> <new-oid> [<old-oid>]
+               [-m <reason>] [--no-deref] --stdin [-z] [--batch-updates]
 
 DESCRIPTION
 -----------
@@ -57,6 +59,14 @@ performs all modifications together.  Specify commands of the form:
 With `--create-reflog`, update-ref will create a reflog for each ref
 even if one would not ordinarily be created.
 
+With `--batch-updates`, update-ref executes the updates in a batch but allows
+individual updates to fail due to invalid or incorrect user input, applying only
+the successful updates. However, system-related errors—such as I/O failures or
+memory issues—will result in a full failure of all batched updates. Any failed
+updates will be reported in the following format:
+
+	rejected SP (<old-oid> | <old-target>) SP (<new-oid> | <new-target>) SP <rejection-reason> LF
+
 Quote fields containing whitespace as if they were strings in C source
 code; i.e., surrounded by double-quotes and with backslash escapes.
 Use 40 "0" characters or the empty string to specify a zero value.  To
diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index 1d541e13ad..97e14b279e 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -5,6 +5,7 @@
 #include "config.h"
 #include "gettext.h"
 #include "hash.h"
+#include "hex.h"
 #include "refs.h"
 #include "object-name.h"
 #include "parse-options.h"
@@ -13,7 +14,7 @@
 static const char * const git_update_ref_usage[] = {
 	N_("git update-ref [<options>] -d <refname> [<old-oid>]"),
 	N_("git update-ref [<options>]    <refname> <new-oid> [<old-oid>]"),
-	N_("git update-ref [<options>] --stdin [-z]"),
+	N_("git update-ref [<options>] --stdin [-z] [--batch-updates]"),
 	NULL
 };
 
@@ -565,6 +566,49 @@ static void parse_cmd_abort(struct ref_transaction *transaction,
 	report_ok("abort");
 }
 
+static void print_rejected_refs(const char *refname,
+				const struct object_id *old_oid,
+				const struct object_id *new_oid,
+				const char *old_target,
+				const char *new_target,
+				enum ref_transaction_error err,
+				void *cb_data UNUSED)
+{
+	struct strbuf sb = STRBUF_INIT;
+	const char *reason = "";
+
+	switch (err) {
+	case REF_TRANSACTION_ERROR_NAME_CONFLICT:
+		reason = "refname conflict";
+		break;
+	case REF_TRANSACTION_ERROR_CREATE_EXISTS:
+		reason = "reference already exists";
+		break;
+	case REF_TRANSACTION_ERROR_NONEXISTENT_REF:
+		reason = "reference does not exist";
+		break;
+	case REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE:
+		reason = "incorrect old value provided";
+		break;
+	case REF_TRANSACTION_ERROR_INVALID_NEW_VALUE:
+		reason = "invalid new value provided";
+		break;
+	case REF_TRANSACTION_ERROR_EXPECTED_SYMREF:
+		reason = "expected symref but found regular ref";
+		break;
+	default:
+		reason = "unkown failure";
+	}
+
+	strbuf_addf(&sb, "rejected %s %s %s %s\n", refname,
+		    new_oid ? oid_to_hex(new_oid) : new_target,
+		    old_oid ? oid_to_hex(old_oid) : old_target,
+		    reason);
+
+	fwrite(sb.buf, sb.len, 1, stdout);
+	strbuf_release(&sb);
+}
+
 static void parse_cmd_commit(struct ref_transaction *transaction,
 			     const char *next, const char *end UNUSED)
 {
@@ -573,6 +617,10 @@ static void parse_cmd_commit(struct ref_transaction *transaction,
 		die("commit: extra input: %s", next);
 	if (ref_transaction_commit(transaction, &error))
 		die("commit: %s", error.buf);
+
+	ref_transaction_for_each_rejected_update(transaction,
+						 print_rejected_refs, NULL);
+
 	report_ok("commit");
 	ref_transaction_free(transaction);
 }
@@ -609,7 +657,7 @@ static const struct parse_cmd {
 	{ "commit",        parse_cmd_commit,        0, UPDATE_REFS_CLOSED },
 };
 
-static void update_refs_stdin(void)
+static void update_refs_stdin(unsigned int flags)
 {
 	struct strbuf input = STRBUF_INIT, err = STRBUF_INIT;
 	enum update_refs_state state = UPDATE_REFS_OPEN;
@@ -617,7 +665,7 @@ static void update_refs_stdin(void)
 	int i, j;
 
 	transaction = ref_store_transaction_begin(get_main_ref_store(the_repository),
-						  0, &err);
+						  flags, &err);
 	if (!transaction)
 		die("%s", err.buf);
 
@@ -685,7 +733,7 @@ static void update_refs_stdin(void)
 			 */
 			state = cmd->state;
 			transaction = ref_store_transaction_begin(get_main_ref_store(the_repository),
-								  0, &err);
+								  flags, &err);
 			if (!transaction)
 				die("%s", err.buf);
 
@@ -701,6 +749,8 @@ static void update_refs_stdin(void)
 		/* Commit by default if no transaction was requested. */
 		if (ref_transaction_commit(transaction, &err))
 			die("%s", err.buf);
+		ref_transaction_for_each_rejected_update(transaction,
+						 print_rejected_refs, NULL);
 		ref_transaction_free(transaction);
 		break;
 	case UPDATE_REFS_STARTED:
@@ -727,6 +777,8 @@ int cmd_update_ref(int argc,
 	struct object_id oid, oldoid;
 	int delete = 0, no_deref = 0, read_stdin = 0, end_null = 0;
 	int create_reflog = 0;
+	unsigned int flags = 0;
+
 	struct option options[] = {
 		OPT_STRING( 'm', NULL, &msg, N_("reason"), N_("reason of the update")),
 		OPT_BOOL('d', NULL, &delete, N_("delete the reference")),
@@ -735,6 +787,8 @@ int cmd_update_ref(int argc,
 		OPT_BOOL('z', NULL, &end_null, N_("stdin has NUL-terminated arguments")),
 		OPT_BOOL( 0 , "stdin", &read_stdin, N_("read updates from stdin")),
 		OPT_BOOL( 0 , "create-reflog", &create_reflog, N_("create a reflog")),
+		OPT_BIT('0', "batch-updates", &flags, N_("batch reference updates"),
+			REF_TRANSACTION_ALLOW_FAILURE),
 		OPT_END(),
 	};
 
@@ -756,9 +810,10 @@ int cmd_update_ref(int argc,
 			usage_with_options(git_update_ref_usage, options);
 		if (end_null)
 			line_termination = '\0';
-		update_refs_stdin();
+		update_refs_stdin(flags);
 		return 0;
-	}
+	} else if (flags & REF_TRANSACTION_ALLOW_FAILURE)
+		die("--batch-updates can only be used with --stdin");
 
 	if (end_null)
 		usage_with_options(git_update_ref_usage, options);
diff --git a/t/t1400-update-ref.sh b/t/t1400-update-ref.sh
index 29045aad43..d29d23cb89 100755
--- a/t/t1400-update-ref.sh
+++ b/t/t1400-update-ref.sh
@@ -2066,6 +2066,239 @@ do
 		grep "$(git rev-parse $a) $(git rev-parse $a)" actual
 	'
 
+	test_expect_success "stdin $type batch-updates" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit commit &&
+			head=$(git rev-parse HEAD) &&
+
+			format_command $type "update refs/heads/ref1" "$head" "$Z" >stdin &&
+			format_command $type "update refs/heads/ref2" "$head" "$Z" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin &&
+			echo $head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			git rev-parse refs/heads/ref2 >actual &&
+			test_cmp expect actual
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates with invalid new_oid" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref1 $head &&
+			git update-ref refs/heads/ref2 $head &&
+
+			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
+			format_command $type "update refs/heads/ref2" "$(test_oid 001)" "$head" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			echo $head >expect &&
+			git rev-parse refs/heads/ref2 >actual &&
+			test_cmp expect actual &&
+			test_grep -q "invalid new value provided" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates with non-commit new_oid" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			head_tree=$(git rev-parse HEAD^{tree}) &&
+			git update-ref refs/heads/ref1 $head &&
+			git update-ref refs/heads/ref2 $head &&
+
+			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
+			format_command $type "update refs/heads/ref2" "$head_tree" "$head" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			echo $head >expect &&
+			git rev-parse refs/heads/ref2 >actual &&
+			test_cmp expect actual &&
+			test_grep -q "invalid new value provided" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates with non-existent ref" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref1 $head &&
+
+			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
+			format_command $type "update refs/heads/ref2" "$old_head" "$head" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			test_must_fail git rev-parse refs/heads/ref2 &&
+			test_grep -q "reference does not exist" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates with dangling symref" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref1 $head &&
+			git symbolic-ref refs/heads/ref2 refs/heads/nonexistent &&
+
+			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
+			format_command $type "update refs/heads/ref2" "$old_head" "$head" >>stdin &&
+			git update-ref $type --no-deref --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			echo $head >expect &&
+			test_must_fail git rev-parse refs/heads/ref2 &&
+			test_grep -q "reference does not exist" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates with regular ref as symref" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref1 $head &&
+			git update-ref refs/heads/ref2 $head &&
+
+			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
+			format_command $type "symref-update refs/heads/ref2" "$old_head" "ref" "refs/heads/nonexistent" >>stdin &&
+			git update-ref $type --no-deref --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			echo $head >expect &&
+			echo $head >expect &&
+			git rev-parse refs/heads/ref2 >actual &&
+			test_cmp expect actual &&
+			test_grep -q "expected symref but found regular ref" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates with invalid old_oid" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref1 $head &&
+			git update-ref refs/heads/ref2 $head &&
+
+			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
+			format_command $type "update refs/heads/ref2" "$old_head" "$Z" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			echo $head >expect &&
+			git rev-parse refs/heads/ref2 >actual &&
+			test_cmp expect actual &&
+			test_grep -q "reference already exists" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates with incorrect old oid" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref1 $head &&
+			git update-ref refs/heads/ref2 $head &&
+
+			format_command $type "update refs/heads/ref1" "$old_head" "$head" >stdin &&
+			format_command $type "update refs/heads/ref2" "$head" "$old_head" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref1 >actual &&
+			test_cmp expect actual &&
+			echo $head >expect &&
+			git rev-parse refs/heads/ref2 >actual &&
+			test_cmp expect actual &&
+			test_grep -q "incorrect old value provided" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates refname conflict" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref/foo $head &&
+
+			format_command $type "update refs/heads/ref/foo" "$old_head" "$head" >stdin &&
+			format_command $type "update refs/heads/ref" "$old_head" "" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/ref/foo >actual &&
+			test_cmp expect actual &&
+			test_grep -q "refname conflict" stdout
+		)
+	'
+
+	test_expect_success "stdin $type batch-updates refname conflict new ref" '
+		git init repo &&
+		test_when_finished "rm -fr repo" &&
+		(
+			cd repo &&
+			test_commit one &&
+			old_head=$(git rev-parse HEAD) &&
+			test_commit two &&
+			head=$(git rev-parse HEAD) &&
+			git update-ref refs/heads/ref/foo $head &&
+
+			format_command $type "update refs/heads/foo" "$old_head" "" >stdin &&
+			format_command $type "update refs/heads/ref" "$old_head" "" >>stdin &&
+			git update-ref $type --stdin --batch-updates <stdin >stdout &&
+			echo $old_head >expect &&
+			git rev-parse refs/heads/foo >actual &&
+			test_cmp expect actual &&
+			test_grep -q "refname conflict" stdout
+		)
+	'
 done
 
 test_expect_success 'update-ref should also create reflog for HEAD' '
-- 
2.48.1
Patrick Steinhardt· Mar 24, 2025, 13:08 UTC · re: Karthik Nayak · lore

Re: [PATCH v4 8/8] update-ref: add --batch-updates flag for stdin mode

On Thu, Mar 20, 2025 at 12:44:03PM +0100, Karthik Nayak wrote:
Show 16 quoted lines
> diff --git a/Documentation/git-update-ref.adoc b/Documentation/git-update-ref.adoc
> index 9e6935d38d..5be2c16776 100644
> --- a/Documentation/git-update-ref.adoc
> +++ b/Documentation/git-update-ref.adoc
> @@ -57,6 +59,14 @@ performs all modifications together.  Specify commands of the form:
>  With `--create-reflog`, update-ref will create a reflog for each ref
>  even if one would not ordinarily be created.
>  
> +With `--batch-updates`, update-ref executes the updates in a batch but allows
> +individual updates to fail due to invalid or incorrect user input, applying only
> +the successful updates. However, system-related errors—such as I/O failures or
> +memory issues—will result in a full failure of all batched updates. Any failed
> +updates will be reported in the following format:
> +
> +	rejected SP (<old-oid> | <old-target>) SP (<new-oid> | <new-target>) SP <rejection-reason> LF
> +

Does this support NUL-terminated mode? It probably should, and if it does we should also document the format.

Show 23 quoted lines
> diff --git a/builtin/update-ref.c b/builtin/update-ref.c
> index 1d541e13ad..97e14b279e 100644
> --- a/builtin/update-ref.c
> +++ b/builtin/update-ref.c
> @@ -735,6 +787,8 @@ int cmd_update_ref(int argc,
>  		OPT_BOOL('z', NULL, &end_null, N_("stdin has NUL-terminated arguments")),
>  		OPT_BOOL( 0 , "stdin", &read_stdin, N_("read updates from stdin")),
>  		OPT_BOOL( 0 , "create-reflog", &create_reflog, N_("create a reflog")),
> +		OPT_BIT('0', "batch-updates", &flags, N_("batch reference updates"),
> +			REF_TRANSACTION_ALLOW_FAILURE),
>  		OPT_END(),
>  	};
>  
> @@ -756,9 +810,10 @@ int cmd_update_ref(int argc,
>  			usage_with_options(git_update_ref_usage, options);
>  		if (end_null)
>  			line_termination = '\0';
> -		update_refs_stdin();
> +		update_refs_stdin(flags);
>  		return 0;
> -	}
> +	} else if (flags & REF_TRANSACTION_ALLOW_FAILURE)
> +		die("--batch-updates can only be used with --stdin");
Nit: formatting, the `else if` branch should have curly braces.
Patrick
Karthik Nayak· Mar 24, 2025, 17:51 UTC · re: Patrick Steinhardt · lore

Re: [PATCH v4 8/8] update-ref: add --batch-updates flag for stdin mode

Patrick Steinhardt <ps@pks.im> writes:
Show 21 quoted lines
> On Thu, Mar 20, 2025 at 12:44:03PM +0100, Karthik Nayak wrote:
>> diff --git a/Documentation/git-update-ref.adoc b/Documentation/git-update-ref.adoc
>> index 9e6935d38d..5be2c16776 100644
>> --- a/Documentation/git-update-ref.adoc
>> +++ b/Documentation/git-update-ref.adoc
>> @@ -57,6 +59,14 @@ performs all modifications together.  Specify commands of the form:
>>  With `--create-reflog`, update-ref will create a reflog for each ref
>>  even if one would not ordinarily be created.
>>
>> +With `--batch-updates`, update-ref executes the updates in a batch but allows
>> +individual updates to fail due to invalid or incorrect user input, applying only
>> +the successful updates. However, system-related errors—such as I/O failures or
>> +memory issues—will result in a full failure of all batched updates. Any failed
>> +updates will be reported in the following format:
>> +
>> +	rejected SP (<old-oid> | <old-target>) SP (<new-oid> | <new-target>) SP <rejection-reason> LF
>> +
>
> Does this support NUL-terminated mode? It probably should, and if it
> does we should also document the format.
>

It only does for inputs. So there is nothing to be done for outputs. I actually added support for '-z' mode here, but there was an assumption on my part that this is for both input/output.

Phillip corrected my assumption in the first version of this series [1].
[1]: https://lore.kernel.org/all/ceda422e-8c8e-4a1d-aaab-9a7a2fc009dd@gmail.com/
Show 25 quoted lines
>> diff --git a/builtin/update-ref.c b/builtin/update-ref.c
>> index 1d541e13ad..97e14b279e 100644
>> --- a/builtin/update-ref.c
>> +++ b/builtin/update-ref.c
>> @@ -735,6 +787,8 @@ int cmd_update_ref(int argc,
>>  		OPT_BOOL('z', NULL, &end_null, N_("stdin has NUL-terminated arguments")),
>>  		OPT_BOOL( 0 , "stdin", &read_stdin, N_("read updates from stdin")),
>>  		OPT_BOOL( 0 , "create-reflog", &create_reflog, N_("create a reflog")),
>> +		OPT_BIT('0', "batch-updates", &flags, N_("batch reference updates"),
>> +			REF_TRANSACTION_ALLOW_FAILURE),
>>  		OPT_END(),
>>  	};
>>
>> @@ -756,9 +810,10 @@ int cmd_update_ref(int argc,
>>  			usage_with_options(git_update_ref_usage, options);
>>  		if (end_null)
>>  			line_termination = '\0';
>> -		update_refs_stdin();
>> +		update_refs_stdin(flags);
>>  		return 0;
>> -	}
>> +	} else if (flags & REF_TRANSACTION_ALLOW_FAILURE)
>> +		die("--batch-updates can only be used with --stdin");
>
> Nit: formatting, the `else if` branch should have curly braces.
Ah! Thanks, will change!
> Patrick

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