linux-kernel - Re: Linux 2.6.29

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Message-ID: <f73f7ab80903260549w1619d3a9h588001383026febf@mail.gmail.com>
Date:	Thu, 26 Mar 2009 08:49:52 -0400
From:	Kyle Moffett <kyle@...fetthome.net>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Theodore Tso <tytso@....edu>,
	Christoph Hellwig <hch@...radead.org>, Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...e.de>,
	Jens Axboe <jens.axboe@...cle.com>,
	David Rees <drees76@...il.com>, Jesper Krogh <jesper@...gh.cc>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.29

On Thu, Mar 26, 2009 at 2:24 AM, Jeff Garzik <jeff@...zik.org> wrote:
> Kyle Moffett wrote:
>> Really, I think virtually all of the database programs would be
>> perfectly happy with an "fsbarrier(fd, flags)" syscall, where if "fd"
>> points to a regular file or directory then it instructs the underlying
>> filesystem to do whatever internal barrier it supports, and if not
>> just fail with -ENOTSUPP (so you can fall back to fdatasync(), etc).
>> Perhaps "flags" would allow a "data" or "metadata" barrier, but if not
>> it's not a big issue.
>
> If you want a per-fd barrier call, there is always sync_file_range(2)

The issue is that sync_file_range doesn't seem to be documented to
have any inter-file barrier semantics.  Even then, from the manpage it
doesn't look like
write(fd)+sync_file_range(fd,SYNC_FILE_RANGE_WRITE)+write(fd) would
actually prevent the second write from occurring before the first has
actually hit disk (assuming both are within the specified range).

Cheers,
Kyle Moffett
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