Re: [GIT PULL] block bits for 2.6.29-rc5

[Christoph Hellwig]

On Fri, Feb 20, 2009 at 08:26:35AM +0100, Jens Axboe wrote:
> It seems to work fine for me, tested with a modified sd that doesn't
> have barrier support and loop:
> 
> Filesystem "sdc1": Disabling barriers, trial barrier write failed
> XFS mounting filesystem sdc1
> 
> and
> 
> Filesystem "loop0": Disabling barriers, trial barrier write failed
> XFS mounting filesystem loop0
> 
> No extra failure warnings on the barrier IO itself. What device do you
> see this on?

virtio_blk and loop.  bvut I have investigated this further, and the
reason why I still saw the warnings is that xfs does a
blkdev_issue_flush on unomunt which is not protected by the barrier
flag, so it gets issued unconditionally.  So we got the additional
warning on unmount.  I've sent a patch to make the blkdev_issue_flush
conditionally to fix that issue.

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