Re: [RFC PATCH 1/2] sha1-file: fsync() loose dir entry when core.fsyncObjectFiles

From: Jeff King <peff@peff.net>
Date: Sep 17, 2020, 14:55 UTC
Message-ID: <20200917145523.GB3076467@coredump.intra.peff.net>
In-Reply-To: <20200917140912.GA27653@lst.de>

On Thu, Sep 17, 2020 at 04:09:12PM +0200, Christoph Hellwig wrote:

Show 9 quoted lines

> On Thu, Sep 17, 2020 at 01:28:29PM +0200, Ævar Arnfjörð Bjarmason wrote:
> > 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.
> 
> It is not just paranoia, but indeed what is required from the standards
> POV.  At least for many Linux file systems your second fsync will be
> very cheap (basically a NULL syscall) as the log has alredy been forced
> all the way by the first one, but you can't rely on that.

Is it sufficient to fsync() just the surrounding directory? I.e., if I do:

  mkdir("a");
  mkdir("a/b");
  open("a/b/c", O_WRONLY);

is it enough to fsync() a descriptor pointing to "a/b", or should I also do "a"?

-Peff