Hi Ævar,

On Tue, 22 Sep 2020, Ævar Arnfjörð Bjarmason wrote:

On Thu, Sep 17 2020, Johannes Sixt wrote:

quoted

Am 17.09.20 um 13:28 schrieb Ævar Arnfjörð Bjarmason:

quoted

Change the behavior of core.fsyncObjectFiles to also sync the
directory entry. I don't have a case where this broke, just going by
paranoia and the fsync(2) manual page's guarantees about its behavior.

Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
---
 sha1-file.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/sha1-file.c b/sha1-file.c
index dd65bd5c68..d286346921 100644
--- a/sha1-file.c
+++ b/sha1-file.c

@@ -1784,10 +1784,14 @@ int hash_object_file(const struct git_hash_algo *algo, const void *buf,
 }

 /* Finalize a file on disk, and close it. */
-static void close_loose_object(int fd)
+static void close_loose_object(int fd, const struct strbuf *dirname)
 {
-	if (fsync_object_files)
+	int dirfd;
+	if (fsync_object_files) {
 		fsync_or_die(fd, "loose object file");
+		dirfd = xopen(dirname->buf, O_RDONLY);
+		fsync_or_die(dirfd, "loose object directory");

Did you have the opportunity to verify that this works on Windows?
Opening a directory with open(2), I mean: It's disallowed according to
the docs:
https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/open-wopen?view=vs-2019#return-value

I did not, just did a quick hack for an RFC discussion (didn't even
close() that fd), but if I pursue this I'll do it properly.

Doing some research on it now reveals that we should probably have some
Windows-specific code here, e.g. browsing GNUlib's source code reveals
that it uses FlushFileBuffers(), and that code itself is taken from
sqlite. SQLite also has special-case code for some Unix warts,
e.g. OSX's and AIX's special fsync behaviors in its src/os_unix.c

If I understand correctly, the idea to `fsync()` directories is to ensure
that metadata updates (such as renames) are flushed, too?

If so (and please note that my understanding of NTFS is not super deep in
this regard), I think that we need not worry on Windows. I have come to
believe that the `rename()` operations are flushed pretty much
immediately, without any `FlushFileBuffers()` (or `_commit()`, as we
actually do in `compat/mingw.h`, to convince yourself see
https://github.com/git/git/blob/v2.29.2/compat/mingw.h#L135-L136).

Directories are not mentioned in `FlushFileBuffers()`'s documentation
(https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-flushfilebuffers)
nor in the documentation of `_commit()`:
https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/commit?view=msvc-160

Therefore, I believe that there is not even a Win32 equivalent of
`fsync()`ing directories.

Ciao,
Dscho

quoted

quoted

+	} if (close(fd) != 0) die_errno(_("error when closing loose object
file")); }

-- Hannes