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

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Message-ID: <49945C90.3010104@garzik.org>
Date:	Thu, 12 Feb 2009 12:29:52 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	Eric Sandeen <sandeen@...hat.com>
CC:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>, Jan Kara <jack@...e.cz>,
	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

Eric Sandeen wrote:
> Fernando Luis Vázquez Cao wrote:
>> This mount flag will be used to determine whether the block device's write
>> cache should be flush or not on fsync()/fdatasync().
>>
>> Signed-off-by: Fernando Luis Vazquez Cao <fernando@....ntt.co.jp>
>> ---
> 
> Again, apologies for chiming in late.
> 
> But wouldn't it be better to make this a block device property rather
> than a new filesystem mount option?
> 
> That way the filesystem can always do "the right thing" and call the
> blkdev flush on fsync.
> 
> The block device *could* choose to ignore this in hardware if it knows
> it's built with a nonvolatile write cache or if it has no write cache.

That would certainly be my preference -- turn this ON by default, and 
them if a layer NEEDS to ignore it, it can.

	Jeff




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