lkml.org 
[lkml]   [2006]   [Jan]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 6/9] device-mapper snapshot: barriers not supported
    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"

    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2006-01-23 16:59    [W:0.024 / U:0.344 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site