On 05/30/2014 09:35 AM, Jeff Cody wrote: > Now that node-names can reference an individual BlockDriverState without > needing to navigate downwards from the 'device' level, in order to find > the top-most image (active layer) we need a pointer to the overlay of a > BDS. > > This will allow QMP commands to reference an image solely by its > node-name, without also needing to pass in the corresponding 'device' > string. > > This also adds a helper function to set the overlay pointer that is, for > now, trivial. But since we recently moved away from open coding > bs->backing_hd assignment, we should probably also refrain from setting > bs->overlay directly. > > Signed-off-by: Jeff Cody <jc...@redhat.com> > --- > block.c | 14 ++++++++++++++ > include/block/block.h | 1 + > include/block/block_int.h | 1 + > 3 files changed, 16 insertions(+)
Question - can one bds ever belong to more than one chain? That is,
could I create a guest that uses:
/ disk1
base <
\ disk2
for two disks in parallel, but where I use blockdev referencing to pass
in a single readonly copy of base to both chains rather than the default
of opening base twice? If so, then what does the overlay field get set
to for base: disk1 or disk2? On the other hand, if base truly is
shared, it's non-deterministic which device is meant when using just the
node-name for the shared base bds. So maybe the user gets what they
deserved. Or maybe it argues that doing a bds lookup for a bds that has
more than one device chain returns a failure unless the device chain was
passed as well (but that may mean reference counting or even tracking an
array of overlays).
But if a bds can be in at most one chain at a time, then your patch
makes sense.
Reviewed-by: Eric Blake <ebl...@redhat.com>
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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