Re: [Qemu-devel] [PATCH v2] xen-block: handle resize callback

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Anthony PERARD [mailto:anthony.perard@citrix.com]
> Sent: 31 January 2019 15:25
> To: Paul Durrant <Paul.Durrant@citrix.com>
> Cc: qemu-devel@nongnu.org; qemu-block@nongnu.org; xen-
> devel@lists.xenproject.org; Stefan Hajnoczi <stefanha@redhat.com>; Stefano
> Stabellini <sstabellini@kernel.org>; Kevin Wolf <kwolf@redhat.com>; Max
> Reitz <mreitz@redhat.com>
> Subject: Re: [PATCH v2] xen-block: handle resize callback
> 
> On Thu, Jan 31, 2019 at 03:22:18PM +0000, Paul Durrant wrote:
> > > -----Original Message-----
> > > From: Anthony PERARD [mailto:anthony.perard@citrix.com]
> > > Sent: 31 January 2019 15:21
> > > To: Paul Durrant <Paul.Durrant@citrix.com>
> > > Cc: qemu-devel@nongnu.org; qemu-block@nongnu.org; xen-
> > > devel@lists.xenproject.org; Stefan Hajnoczi <stefanha@redhat.com>;
> Stefano
> > > Stabellini <sstabellini@kernel.org>; Kevin Wolf <kwolf@redhat.com>;
> Max
> > > Reitz <mreitz@redhat.com>
> > > Subject: Re: [PATCH v2] xen-block: handle resize callback
> > >
> > > On Wed, Jan 30, 2019 at 04:19:48PM +0000, Paul Durrant wrote:
> > > > Some frontend drivers will handle dynamic resizing of PV disks, so
> set
> > > up
> > > > the BlockDevOps resize_cb() method during xen_block_realize() to
> allow
> > > > this to be done.
> > > >
> > > > Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> > > > ---
> > >
> > >
> > > > +    /*
> > > > +     * Mimic the behaviour of Linux xen-blkback and re-write the
> state
> > > > +     * to trigger the frontend watch.
> > > > +     */
> > > > +    xen_device_backend_set_state(xendev, backend_state);
> > >
> > > :(, that function doesn't write the state again if it hasn't changed.
> > > So in my testing, Linux never did anything.
> >
> > Gah! I forgot about that. Alright, it's going to have to be a bit more
> crude.
> 
> more crude > Yes, I tried to ignore the check in _set_state and end-up
> with an infinit loop.

Yes, you would. That check is there for a reason :-) I'll replace the call in xen-block.c with a call to xen_device_backend_printf().

  Paul

> 
> --
> Anthony PERARD