linux-kernel - Re: [RFC PATCH] fpathconf() for fsync() behavior

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 22 Apr 2009 22:17:48 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Valerie Aurora Henson <vaurora@...hat.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Chris Mason <chris.mason@...cle.com>,
	Theodore Tso <tytso@....edu>,
	Eric Sandeen <sandeen@...hat.com>,
	Ric Wheeler <rwheeler@...hat.com>
Subject: Re: [RFC PATCH] fpathconf() for fsync() behavior

On Wed, 22 Apr 2009 20:12:57 -0400 Valerie Aurora Henson <vaurora@...hat.com> wrote:

> In the default mode for ext3 and btrfs, fsync() is both slow and
> unnecessary for some important application use cases - at the same
> time that it is absolutely required for correctness for other modes of
> ext3, ext4, XFS, etc.  If applications could easilyl distinguish
> between the two cases, they would be more likely to be correct and
> fast.
> 
> How about an fpathconf() variable, something like _PC_ORDERED?  E.g.:
> 
> 	/* Unoptimized example optional fsync() demo */
> 	write(fd);
> 	/* Only fsync() if we need it */
> 	if (fpath_conf(fd, _PC_ORDERED) != 1)
> 		fsync(fd);
> 	rename(tmp_path, new_path);
> 
> I know of two specific real-world cases in which this would
> significantly improve performance: (a) fsync() before rename(), (b)
> fsync() of the parent directory of a newly created file.  Case (b) is
> particularly nasty when you have multiple threads creating files in
> the same directory because the dir's i_mutex is held across fsync() -
> file creates become limited to the speed of sequential fsync()s.
> 
> Conceptual libc patch below.

Would it be better to implement new syscall(s) with finer-grained control
and better semantics?  Then userspace would just need to to:

	fsync_on_steroids(fd, FSYNC_BEFORE_RENAME);

and that all gets down into the filesystem which can then work out what
it needs to do to implement the command.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/