linux-kernel - Re: vfs: Add MS_FLUSHONFSYNC mount flag

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Message-ID: <499494E2.3060006@redhat.com>
Date:	Thu, 12 Feb 2009 15:30:10 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Jan Kara <jack@...e.cz>
CC:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>, Theodore Tso <tytso@....EDU>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Pavel Machek <pavel@...e.cz>,
	kernel list <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>, fernando@....ac.jp,
	Ric Wheeler <rwheeler@...hat.com>
Subject: Re: vfs: Add MS_FLUSHONFSYNC mount flag

Jan Kara wrote:
> On Thu 12-02-09 11:13:37, Eric Sandeen wrote:

...

>> Also that way if you have 8 partitions on a battery-backed blockdev, you
>> can tune it once, instead of needing to mount all 8 filesystems with the
>> new option.
>   Yes, but OTOH we should give sysadmin a possibility to enable / disable
> it on just some partitions. I don't see a reasonable use for that but people
> tend to do strange things ;) and here isn't probably a strong reason to not
> allow them.
> 
> 								Honza

But nobody has asked for that, have they?  So why offer it up a this point?

They could use LD_PRELOAD to make fsync a no-op if they really don't
care for it, I guess... though that's not easily per-fs either.

But do we really want to go out of our way to enable people to
short-circuit data integrity paths and then file bugs when their files
go missing? :)

(I guess the blockdev tunable is similarly dangerous, but it more
clearly meets the explicit need (writecache-safe devices))

-Eric
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