Re: [Xen-devel] [PATCH] migration, xen: Fix block image lock issue on live migration

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Anthony,

On 29/11/17 15:06, Anthony PERARD wrote:
> On Wed, Nov 29, 2017 at 12:28:39PM +0000, Julien Grall wrote:
> > + Stefano
> >
> > On 11/27/2017 03:00 PM, Anthony PERARD wrote:
> > > Hi Julien,
> > Hi Anthony,
> >
> > > Can I get a release-ack for this patch?
> > >
> > > This fix local live migration of HVM guest when the disk backend is
> > > qdisk.  osstest doesn't report a regression because the kernel or the
> > > glibc is just a bit too old.
> > When does that regression happen? I am considering to release Xen 4.10 soon
> > and would need more details to decide the inclusion of the patch.
> That can happen when an API call Open File Description Locks
> (F_OFD_GETLK and F_OFD_SETLK) is available. There are since Linux 3.15
> and glibc 2.20.
>
> When this API is available, QEMU is going to set a lock on the file open
> for a block device. When we try to live migrate a guest and the lock is
> set, the new QEMU is going to fail to open the disk with an error
> message that say something like "file locked", and migration fail.
>
> The scenario when the lock is an issue are:
> - an HVM guest which us qdisk for disk backend. (Like when the disk
>    image is in a format different than raw. e.g. qcow2)
> - an HVM guest which only use emulated disk.
>
>
> BUT I can't reproduce the issue with the QEMU we are going to release...
> so there is probably a race involve. I guess the patch can wait.
I will defer it to Xen 4.11. We might want to Release notes thought.

Cheers,

--
Julien Grall

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