[PATCH v13 0/7] unpack-objects: support streaming blobs to disk

This series makes "unpack-objects" capable of streaming large objects to disk.

As 7/7 shows streaming e.g. a 100MB blob now uses ~5MB of memory instead of ~105MB. This streaming method is slower if you've got memory to handle the blobs in-core, but if you don't it allows you to unpack objects at all, as you might otherwise OOM.

This series by Han Xin was originally waiting on some in-flight patches that landed in 430883a70c7 (Merge branch 'ab/object-file-api-updates', 2022-03-16), and until yesterday with 83937e95928 (Merge branch 'ns/batch-fsync', 2022-06-03) had a textual and semantic conflict with "master".

Changes since v12:

 * Since v12 Han Xin submitted 1/1 here as
   https://lore.kernel.org/git/cover.1653015534.git.chiyutianyi@gmail.com/;
   I think this is better off reviewed as a whole, and hopefully will
   be picked up as such.

 * Dropped the previous 7/8, which was a refactoring to make 8/8
   slightly smaller. Per dicsussion with René it's better to leave it
   out.

 * The rest (especially 2/8) is due to rebasing on ns/batch-fsync.

Han Xin (4):
  unpack-objects: low memory footprint for get_data() in dry_run mode
  object-file.c: refactor write_loose_object() to several steps
  object-file.c: add "stream_loose_object()" to handle large object
  unpack-objects: use stream_loose_object() to unpack large objects

Ævar Arnfjörð Bjarmason (3):
  object-file.c: do fsync() and close() before post-write die()
  object-file.c: factor out deflate part of write_loose_object()
  core doc: modernize core.bigFileThreshold documentation

 Documentation/config/core.txt   |  33 +++--
 builtin/unpack-objects.c        | 103 ++++++++++++--
 object-file.c                   | 237 +++++++++++++++++++++++++++-----
 object-store.h                  |   8 ++
 t/t5351-unpack-large-objects.sh |  61 ++++++++
 5 files changed, 387 insertions(+), 55 deletions(-)
 create mode 100755 t/t5351-unpack-large-objects.sh

Range-diff against v12:
1:  e95f6a1cfb6 = 1:  12873fc9915 unpack-objects: low memory footprint for get_data() in dry_run mode
2:  54060eb8c6b ! 2:  b3568f0c5c0 object-file.c: do fsync() and close() before post-write die()
    @@ Commit message
         Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
      ## object-file.c ##
    -@@ object-file.c: void hash_object_file(const struct git_hash_algo *algo, const void *buf,
    - 	hash_object_file_literally(algo, buf, len, type_name(type), oid);
    - }
    - 
    --/* Finalize a file on disk, and close it. */
    -+/*
    -+ * We already did a write_buffer() to the "fd", let's fsync()
    -+ * and close().
    -+ *
    -+ * Finalize a file on disk, and close it. We might still die() on a
    -+ * subsequent sanity check, but let's not add to that confusion by not
    -+ * flushing any outstanding writes to disk first.
    -+ */
    - static void close_loose_object(int fd)
    - {
    - 	if (the_repository->objects->odb->will_destroy)
     @@ object-file.c: static int write_loose_object(const struct object_id *oid, char *hdr,
      		die(_("deflateEnd on object %s failed (%d)"), oid_to_hex(oid),
      		    ret);
      	the_hash_algo->final_oid_fn(&parano_oid, &c);
    -+	close_loose_object(fd);
    ++	close_loose_object(fd, tmp_file.buf);
     +
      	if (!oideq(oid, &parano_oid))
      		die(_("confused by unstable object source data for %s"),
      		    oid_to_hex(oid));
      
    --	close_loose_object(fd);
    +-	close_loose_object(fd, tmp_file.buf);
     -
      	if (mtime) {
      		struct utimbuf utb;
3:  3dcaa5d6589 ! 3:  9dc0f56878a object-file.c: refactor write_loose_object() to several steps
    @@ object-file.c: static int write_loose_object(const struct object_id *oid, char *
     -		    ret);
     -	the_hash_algo->final_oid_fn(&parano_oid, &c);
     +		die(_("deflateEnd on object %s failed (%d)"), oid_to_hex(oid), ret);
    - 	close_loose_object(fd);
    + 	close_loose_object(fd, tmp_file.buf);
      
      	if (!oideq(oid, &parano_oid))
4:  03f4e91ac89 = 4:  a0434835fe7 object-file.c: factor out deflate part of write_loose_object()
5:  3d64cf1cf33 ! 5:  0b07b29836b object-file.c: add "stream_loose_object()" to handle large object
    @@ object-file.c: static int freshen_packed_object(const struct object_id *oid)
     +	ret = end_loose_object_common(&c, &stream, oid);
     +	if (ret != Z_OK)
     +		die(_("deflateEnd on stream object failed (%d)"), ret);
    -+	close_loose_object(fd);
    ++	close_loose_object(fd, tmp_file.buf);
     +
     +	if (freshen_packed_object(oid) || freshen_loose_object(oid)) {
     +		unlink_or_warn(tmp_file.buf);
6:  33ffcbbc1f0 = 6:  5ed79c58b18 core doc: modernize core.bigFileThreshold documentation
7:  11f7aa026b4 < -:  ----------- unpack-objects: refactor away unpack_non_delta_entry()
8:  34ee6a28a54 ! 7:  5bc8fa9bc8d unpack-objects: use stream_loose_object() to unpack large objects
    @@ Documentation/config/core.txt: usage, at the slight expense of increased disk us
      	Specifies the pathname to the file that contains patterns to
     
      ## builtin/unpack-objects.c ##
    -@@ builtin/unpack-objects.c: static void added_object(unsigned nr, enum object_type type,
    - 	}
    +@@ builtin/unpack-objects.c: static void unpack_non_delta_entry(enum object_type type, unsigned long size,
    + 		write_object(nr, type, buf, size);
      }
      
     +struct input_zstream_data {
    @@ builtin/unpack-objects.c: static void added_object(unsigned nr, enum object_type
      				void *delta_data, unsigned long delta_size)
      {
     @@ builtin/unpack-objects.c: static void unpack_one(unsigned nr)
    + 	}
      
      	switch (type) {
    - 	case OBJ_BLOB:
    ++	case OBJ_BLOB:
     +		if (!dry_run && size > big_file_threshold) {
     +			stream_blob(size, nr);
     +			return;
    @@ builtin/unpack-objects.c: static void unpack_one(unsigned nr)
     +		/* fallthrough */
      	case OBJ_COMMIT:
      	case OBJ_TREE:
    +-	case OBJ_BLOB:
      	case OBJ_TAG:
    + 		unpack_non_delta_entry(type, size, nr);
    + 		return;
     
      ## t/t5351-unpack-large-objects.sh ##
     @@ t/t5351-unpack-large-objects.sh: test_description='git unpack-objects with large objects'