Re: [Qemu-devel] [PATCH for-2.7 v2 07/17] rbd: Implement image locking

[Fam Zheng <famz@redhat.com>]

On Wed, 04/27 13:18, Jason Dillaman wrote:
> On Tue, Apr 26, 2016 at 7:20 PM, Fam Zheng <famz@redhat.com> wrote:
> > On Tue, 04/26 10:42, Jason Dillaman wrote:
> >> On Sun, Apr 24, 2016 at 7:42 PM, Fam Zheng <famz@redhat.com> wrote:
> >> > On Fri, 04/22 21:57, Jason Dillaman wrote:
> >> >> Since this cannot automatically recover from a crashed QEMU client with an
> >> >> RBD image, perhaps this RBD locking should not default to enabled.
> >> >> Additionally, this will conflict with the "exclusive-lock" feature
> >> >> available since the Ceph Hammer-release since both utilize the same locking
> >> >> construct.
> >> >>
> >> >> As a quick background, the optional exclusive-lock feature can be
> >> >> enabled/disabled on image and safely/automatically handles the case of
> >> >> recovery from a crashed client.  Under normal conditions, the RBD
> >> >> exclusive-lock feature automatically acquires the lock upon the first
> >> >> attempt to write to the image and transparently transitions ownership of
> >> >> the lock between two or more clients -- used for QEMU live-migration.
> >> >
> >> > Is it enabled by default?
> >> >
> >>
> >> Starting with the Jewel release of Ceph it is enabled by default.
> >
> > OK, then I'll leave rbd in this QEMU series for now.
> 
> Without exposing some new API methods, this patch will, unfortunately,
> directly conflict with the new Jewel rbd defaults and will actually
> result in the image becoming read-only since librbd won't be able to
> acquire the exclusive lock when QEMU owns the advisory lock.
> 
> We can probably get the new API methods upstream within a week or two
> [1].  If that's too long of a delay, I'd recommend dropping rbd
> locking from the series for now.

Yes you are right, I tried to mean "drop" with "leave" :)

Thanks,
Fam

> 
> [1] http://tracker.ceph.com/issues/15632
> 
> -- 
> Jason