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SubjectRe: [PATCH 6/9] device-mapper snapshot: barriers not supported
Lars Marowsky-Bree <lmb@suse.de> wrote:
>
> 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 ;-)
>

I don't understand that, sorry.

My concern is: has the above change any potential to cause
currently-working setups to stop working?

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