Messages in this thread | | | Date | Mon, 23 Jan 2006 16:56:05 +0100 | From | Lars Marowsky-Bree <> | Subject | Re: [PATCH 6/9] device-mapper snapshot: barriers not supported |
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On 2006-01-22T21:41:11, Andrew Morton <akpm@osdl.org> wrote:
> Alasdair G Kergon <agk@redhat.com> wrote: > > > > The snapshot and origin targets are incapable of handling barriers and > > need to indicate this. > > > > ... > > > > + if (unlikely(bio_barrier(bio))) > > + return -EOPNOTSUPP; > > + > > And what was happening if people _were_ sending such BIOs down? Did it all > appear to work correctly? If so, will this change cause > currently-apparently-working setups to stop working?
Filesystems basically disable using barriers on a device which doesn't support them, which is indicated by -EOPNOTSUPP. Barriers are allowed to fail in such fashion.
Now the interesting question is what happens when barriers are suddenly verboten on a stack which used to support them - because the new mapping doesn't support it _anymore_. Hrm. _Should_ work, but probably not tested much ;-)
Sincerely, Lars Marowsky-Brée
-- High Availability & Clustering SUSE Labs, Research and Development SUSE LINUX Products GmbH - A Novell Business -- Charles Darwin "Ignorance more frequently begets confidence than does knowledge"
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