From: Lars Marowsky-Bree <lmb@suse.de>
To: Andrew Morton <akpm@osdl.org>, Alasdair G Kergon <agk@redhat.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH 6/9] device-mapper snapshot: barriers not supported
Date: Mon, 23 Jan 2006 16:56:05 +0100 [thread overview]
Message-ID: <20060123155605.GP2366@marowsky-bree.de> (raw)
In-Reply-To: <20060122214111.11170cdc.akpm@osdl.org>
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"
next prev parent reply other threads:[~2006-01-23 15:57 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-20 21:17 [PATCH 6/9] device-mapper snapshot: barriers not supported Alasdair G Kergon
2006-01-23 5:41 ` Andrew Morton
2006-01-23 15:56 ` Lars Marowsky-Bree [this message]
2006-01-23 21:14 ` Andrew Morton
2006-01-25 20:55 ` Alasdair G Kergon
2006-01-23 17:01 ` Alasdair G Kergon
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