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[PATCH v3 13/19] initial_ref_transaction_commit(): check for ref D/F conflicts

From
Michael Haggerty <mhagger@alum.mit.edu>
Date
Jun 22, 2015, 14:03 UTC
Message-ID
<5320ec28e09bda9cc1f8a1b9748b8de014bd8ffe.1434980615.git.mhagger@alum.mit.edu>
In-Reply-To
<cover.1434980615.git.mhagger@alum.mit.edu>

In initial_ref_transaction_commit(), check for D/F conflicts (i.e., the type of conflict that exists between "refs/foo" and "refs/foo/bar") among the references being created and between the references being created and any hypothetical existing references.

Ideally, there shouldn't *be* any existing references when this function is called. But, at least in the case of the "testgit" remote helper, "clone" can be called after the remote-tracking "HEAD" and "master" branches have already been created. So let's just do the full-blown check.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
---
Notes (discussion):
    I'm a bit torn on this commit. Part of me says that we should avoid
    the overhead of the extra checks against loose_refs and packed_refs
    because there shouldn't be any references there anyway. Instead, the
    "testgit" remote helper should be fixed.
    
    But these tests should be pretty cheap, and we would want to check for
    ref D/F conflicts among the new references in any case, so it seems
    safer to include these checks. Also, our documentation suggests that
    users refer to git-remote-testgit(1) as an example when writing their
    own remote helpers, so it could be that there is other code out there
    that has imitated its light misuse of this functionality.
 refs.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)
diff --git a/refs.c b/refs.c
index 53d9e45..4513ec7 100644
--- a/refs.c
+++ b/refs.c
@@ -4081,9 +4081,19 @@ cleanup:
 	return ret;
 }
 
+static int ref_present(const char *refname,
+		       const struct object_id *oid, int flags, void *cb_data)
+{
+	struct string_list *affected_refnames = cb_data;
+
+	return string_list_has_string(affected_refnames, refname);
+}
+
 int initial_ref_transaction_commit(struct ref_transaction *transaction,
 				   struct strbuf *err)
 {
+	struct ref_dir *loose_refs = get_loose_refs(&ref_cache);
+	struct ref_dir *packed_refs = get_packed_refs(&ref_cache);
 	int ret = 0, i;
 	int n = transaction->nr;
 	struct ref_update **updates = transaction->updates;
@@ -4103,12 +4113,36 @@ int initial_ref_transaction_commit(struct ref_transaction *transaction,
 		goto cleanup;
 	}
 
+	/*
+	 * It's really undefined to call this function in an active
+	 * repository or when there are existing references: we are
+	 * only locking and changing packed-refs, so (1) any
+	 * simultaneous processes might try to change a reference at
+	 * the same time we do, and (2) any existing loose versions of
+	 * the references that we are setting would have precedence
+	 * over our values. But some remote helpers create the remote
+	 * "HEAD" and "master" branches before calling this function,
+	 * so here we really only check that none of the references
+	 * that we are creating already exists.
+	 */
+	if (for_each_rawref(ref_present, &affected_refnames))
+		die("BUG: initial ref transaction called with existing refs");
+
 	for (i = 0; i < n; i++) {
 		struct ref_update *update = updates[i];
 
 		if ((update->flags & REF_HAVE_OLD) &&
 		    !is_null_sha1(update->old_sha1))
 			die("BUG: initial ref transaction with old_sha1 set");
+		if (verify_refname_available(update->refname,
+					     &affected_refnames, NULL,
+					     loose_refs, err) ||
+		    verify_refname_available(update->refname,
+					     &affected_refnames, NULL,
+					     packed_refs, err)) {
+			ret = TRANSACTION_NAME_CONFLICT;
+			goto cleanup;
+		}
 	}
 
 	if (lock_packed_refs(0)) {

-- 
2.1.4
Previous: Junio C HamanoNext: Michael Haggerty
Message 17 of 24 in “Improve "refs" encapsulation and speed up deletes”
  1. 00/19 Improve "refs" encapsulation and speed up deletesMichael Haggerty, Jun 22, 2015
  2. 01/19 delete_ref(): move declaration to refs.hMichael Haggerty, Jun 22, 2015
  3. 02/19 remove_branches(): remove temporaryMichael Haggerty, Jun 22, 2015
  4. 03/19 delete_ref(): handle special case more explicitlyMichael Haggerty, Jun 22, 2015
  5. 04/19 delete_refs(): new function for the refs APIMichael Haggerty, Jun 22, 2015
  6. 05/19 delete_refs(): make error message more genericMichael Haggerty, Jun 22, 2015
  7. 06/19 delete_refs(): bail early if the packed-refs file cannot be rewrittenMichael Haggerty, Jun 22, 2015
  8. 07/19 prune_remote(): use delete_refs()Michael Haggerty, Jun 22, 2015
  9. 08/19 prune_refs(): use delete_refs()Michael Haggerty, Jun 22, 2015
  10. 09/19 repack_without_refs(): make function privateMichael Haggerty, Jun 22, 2015
  11. 10/19 initial_ref_transaction_commit(): function for initial ref creationMichael Haggerty, Jun 22, 2015
  12. 11/19 refs: remove some functions from the module's public interfaceMichael Haggerty, Jun 22, 2015
  13. 12/19 initial_ref_transaction_commit(): check for duplicate refsMichael Haggerty, Jun 22, 2015
  14. Junio C HamanoJun 22, 2015
  15. Michael HaggertyJun 23, 2015
  16. Junio C HamanoJun 23, 2015
  17. 13/19 initial_ref_transaction_commit(): check for ref D/F conflictsMichael Haggerty, Jun 22, 2015
  18. 14/19 refs: move the remaining ref module declarations to refs.hMichael Haggerty, Jun 22, 2015
  19. 15/19 refs.h: add some parameter names to function declarationsMichael Haggerty, Jun 22, 2015
  20. 16/19 check_branch_commit(): make first parameter constMichael Haggerty, Jun 22, 2015
  21. 17/19 update_ref(): don't read old reference value before deleteMichael Haggerty, Jun 22, 2015
  22. 18/19 cmd_update_ref(): make logic more straightforwardMichael Haggerty, Jun 22, 2015
  23. 19/19 delete_ref(): use the usual convention for old_sha1Michael Haggerty, Jun 22, 2015
  24. Junio C HamanoJun 22, 2015

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