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SubjectRe: [PATCH 6/9] device-mapper snapshot: barriers not supported
On Sun, Jan 22, 2006 at 09:41:11PM -0800, Andrew Morton wrote:
> Alasdair G Kergon <agk@redhat.com> wrote:
> > The snapshot and origin targets are incapable of handling barriers and
> > need to indicate this.

> And what was happening if people _were_ sending such BIOs down? Did it all
> appear to work correctly?

The snapshot target ignores the barrier and in some circumstances I/O can be
reordered in ways that are meant to be prevented by the barrier.

> If so, will this change cause
> currently-apparently-working setups to stop working?

As Lars pointed out, filesystems should already cope with -EOPNOTSUPP
transparently, and it would be sensible for any out-of-tree users to
do likewise.

Alasdair
--
agk@redhat.com
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