[libvirt] [PATCH 3/8] qemu: hotplug: Use new source when preparing/translating for media change

[Peter Krempa]

On Tue, Oct 02, 2018 at 08:15:07 -0400, John Ferlan wrote:
> 
> 
> On 9/27/18 11:09 AM, Peter Krempa wrote:
> > Some internal helpers use only a virDomainDiskDef to do their job. If we
> > want to change source for the disk we need to update it to the new
> > source in the disk definition for those to work correctly.
> > 
> > Signed-off-by: Peter Krempa <pkrempa at redhat.com>
> > ---
> >  src/qemu/qemu_hotplug.c | 11 +++++++++--
> >  1 file changed, 9 insertions(+), 2 deletions(-)
> > 
> > diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
> > index 86afda636e..3043b3257b 100644
> > --- a/src/qemu/qemu_hotplug.c
> > +++ b/src/qemu/qemu_hotplug.c
> > @@ -730,9 +730,12 @@ qemuDomainChangeEjectableMedia(virQEMUDriverPtr driver,
> >                                 bool force)
> >  {
> >      qemuDomainObjPrivatePtr priv = vm->privateData;
> > +    virStorageSourcePtr oldsrc = disk->src;
> >      int ret = -1;
> >      int rc;
> > 
> > +    disk->src = newsrc;
> > +
> 
> Doesn't seem like this would be right especially considering what each
> of the following calls passing both @disk and @newsrc do.
> 
> >      if (qemuHotplugPrepareDiskAccess(driver, vm, disk, newsrc, false) < 0)
> >          goto cleanup;
> 
> Passing both @disk and @newsrc here after assigning newsrc into
> disk->src would seem to do nothing since it temporarily swaps them for
> processing, then returns with them swapped back.

Umm, well it's kind of pointless to pass in newsrc, but it's the exactly
expected behaviour. We want to prepare 'newsrc' but half of the
functions take disk->src directly.

> 
> Shortly after this passing both @disk and @newsrc into either
> qemuDomainChangeMediaBlockdev or qemuDomainChangeMediaLegacy would seem
> to be incorrect especially since each deals with what's in the drive
> first which would now be incorrect, wouldn't it?

Hmm, yeah, the blockdev version actually does care what the old source
was, so that would not work.

The non-blockdev version does not care so it does'nt matter much.

I'll have to change qemuDomainChangeMediaBlockdev to take 'oldsrc'
instead of 'newsrc'.

> 
> > 
> > @@ -744,7 +747,7 @@ qemuDomainChangeEjectableMedia(virQEMUDriverPtr driver,
> >      else
> >          rc = qemuDomainChangeMediaLegacy(driver, vm, disk, newsrc, force);
> > 
> > -    virDomainAuditDisk(vm, disk->src, newsrc, "update", rc >= 0);
> > +    virDomainAuditDisk(vm, oldsrc, newsrc, "update", rc >= 0);
> > 
> >      if (rc < 0) {
> >          ignore_value(qemuHotplugPrepareDiskAccess(driver, vm, disk, newsrc, true));
> 
> This portion would seemingly be problematic too.

As explained above, the only thing that happens is that disk->src is
replaced and reverted again, thus 3 extra assignments.