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From: Christoph Hellwig <hch@lst.de>
To: Jeff King <peff@peff.net>
Cc: Christoph Hellwig <hch@lst.de>,
	git@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] enable core.fsyncObjectFiles by default
Date: Wed, 17 Jan 2018 22:10:11 +0100
Message-ID: <20180117211011.GA355@lst.de> (raw)
In-Reply-To: <20180117205509.GA14828@sigill.intra.peff.net>

On Wed, Jan 17, 2018 at 03:55:09PM -0500, Jeff King wrote:
> I'm definitely sympathetic, and I've contemplated a patch like this a
> few times. But I'm not sure we're "safe by default" here after this
> patch. In particular:
> 
>   1. This covers only loose objects. We generally sync pack writes
>      already, so we're covered there. But we do not sync ref updates at
>      all, which we'd probably want to in a default-safe setup (a common
>      post-crash symptom I've seen is zero-length ref files).

I've not seen them myself yet, but yes, they need an fsync.

>   2. Is it sufficient to fsync() the individual file's descriptors?
>      We often do other filesystem operations (like hardlinking or
>      renaming) that also need to be committed to disk before an
>      operation can be considered saved.

No, for metadata operations we need to fsync the directory as well.

>   3. Related to (2), we often care about the order of metadata commits.
>      E.g., a common sequence is:
> 
>        a. Write object contents to tempfile.
> 
>        b. rename() or hardlink tempfile to final name.
> 
>        c. Write object name into ref.lock file.
> 
>        d. rename() ref.lock to ref
> 
>      If we see (d) but not (b), then the result is a corrupted
>      repository. Is this guaranteed by ext4 journaling with
>      data=ordered?

It is not generally guranteed by Linux file system semantics.  Various
file system will actually start writeback of file data before rename,
but not actually wait on it.

  reply index

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-17 18:48 Christoph Hellwig
2018-01-17 19:04 ` Junio C Hamano
2018-01-17 19:35   ` Christoph Hellwig
2018-01-17 20:05     ` Andreas Schwab
2018-01-17 19:37   ` Matthew Wilcox
2018-01-17 19:42     ` Christoph Hellwig
2018-01-17 21:44   ` Ævar Arnfjörð Bjarmason
2018-01-17 22:07     ` Linus Torvalds
2018-01-17 22:25       ` Linus Torvalds
2018-01-17 23:16       ` Ævar Arnfjörð Bjarmason
2018-01-17 23:42         ` Linus Torvalds
2018-01-17 23:52       ` Theodore Ts'o
2018-01-17 23:57         ` Linus Torvalds
2018-01-18 16:27           ` Christoph Hellwig
2018-01-19 19:08             ` Junio C Hamano
2018-01-20 22:14               ` Theodore Ts'o
2018-01-20 22:27                 ` Junio C Hamano
2018-01-22 15:09                   ` Ævar Arnfjörð Bjarmason
2018-01-22 18:09                     ` Theodore Ts'o
2018-01-23  0:47                       ` Jeff King
2018-01-23  5:45                         ` Theodore Ts'o
2018-01-23 16:17                           ` Jeff King
2018-01-23  0:25                     ` Jeff King
2018-01-21 21:32             ` Chris Mason
2020-09-17 11:06         ` Ævar Arnfjörð Bjarmason
2020-09-17 11:28           ` [RFC PATCH 0/2] should core.fsyncObjectFiles fsync the dir entry + docs Ævar Arnfjörð Bjarmason
2020-09-17 11:28           ` [RFC PATCH 1/2] sha1-file: fsync() loose dir entry when core.fsyncObjectFiles Ævar Arnfjörð Bjarmason
2020-09-17 13:16             ` Jeff King
2020-09-17 15:09               ` Christoph Hellwig
2020-09-17 14:09             ` Christoph Hellwig
2020-09-17 14:55               ` Jeff King
2020-09-17 14:56                 ` Christoph Hellwig
2020-09-17 15:37                   ` Junio C Hamano
2020-09-17 17:12                     ` Jeff King
2020-09-17 20:37                       ` Taylor Blau
2020-09-22 10:42               ` Ævar Arnfjörð Bjarmason
2020-09-17 20:21             ` Johannes Sixt
2020-09-22  8:24               ` Ævar Arnfjörð Bjarmason
2020-11-19 11:38                 ` Johannes Schindelin
2020-09-17 11:28           ` [RFC PATCH 2/2] core.fsyncObjectFiles: make the docs less flippant Ævar Arnfjörð Bjarmason
2020-09-17 14:12             ` Christoph Hellwig
2020-09-17 15:43             ` Junio C Hamano
2020-09-17 20:15               ` Johannes Sixt
2020-10-08  8:13               ` Johannes Schindelin
2020-10-08 15:57                 ` Ævar Arnfjörð Bjarmason
2020-10-08 18:53                   ` Junio C Hamano
2020-10-09 10:44                   ` Johannes Schindelin
2020-09-17 19:21             ` Marc Branchaud
2020-09-17 14:14           ` [PATCH] enable core.fsyncObjectFiles by default Christoph Hellwig
2020-09-17 15:30           ` Junio C Hamano
2018-01-17 20:55 ` Jeff King
2018-01-17 21:10   ` Christoph Hellwig [this message]
  -- strict thread matches above, loose matches on Subject: below --
2015-06-23 21:57 [PATCH] Enable " Stefan Beller
2015-06-23 22:21 ` Junio C Hamano
2015-06-23 23:29   ` Theodore Ts'o
2015-06-24  5:32     ` Junio C Hamano
2015-06-24 14:30       ` Theodore Ts'o
2015-06-24  1:07 ` Duy Nguyen
2015-06-24  3:37 ` Jeff King
2015-06-24  5:20   ` Junio C Hamano

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