Re: [PATCH v2 2/3] wrapper: provide function to sync directories

[[PGP Signed Part:Undecided]]
In ec983eb5d2 (core.fsyncobjectfiles: batched disk flushes, 2021-10-04),
we have introduced batched syncing of object files. This mode works by
only requesting a writeback of the page cache backing the file on
written files, followed by a single hardware-flush via a temporary file
created in the directory we want to flush. Given modern journaling file
systems, this pattern is expected to be durable.

While it's possible to reuse the `git_fsync()` helper to synchronize the
page cache only, there is no helper which would allow for doing a
hardware flush of a directory by creating a temporary file. Other
callers which want to follow the same pattern would thus have to repeat
this logic.

Extract a new helper `git_fsync_dir()` from the object files code which
neatly encapsulates this logic such that it can be reused.

Signed-off-by: Patrick Steinhardt <redacted>
---
 bulk-checkin.c    | 13 +++----------
 git-compat-util.h |  7 +++++++
 wrapper.c         | 21 +++++++++++++++++++++
 3 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/bulk-checkin.c b/bulk-checkin.c
index 4deee1af46..e6ebdd1db5 100644
--- a/bulk-checkin.c
+++ b/bulk-checkin.c

@@ -98,16 +98,9 @@ static void do_batch_fsync(void)
 	 * hardware.
 	 */
 
-	if (needs_batch_fsync) {
-		struct strbuf temp_path = STRBUF_INIT;
-		struct tempfile *temp;
-
-		strbuf_addf(&temp_path, "%s/bulk_fsync_XXXXXX", get_object_directory());
-		temp = xmks_tempfile(temp_path.buf);
-		fsync_or_die(get_tempfile_fd(temp), get_tempfile_path(temp));
-		delete_tempfile(&temp);
-		strbuf_release(&temp_path);
-	}
+	if (needs_batch_fsync &&
+	    git_fsync_dir(get_object_directory()) < 0)
+		die_errno("fsyncing object directory");