On Mon, Sep 28, 2020 at 09:33:22AM -0500, Eric Blake wrote: > On 9/26/20 2:33 AM, Richard W.M. Jones wrote: > >On Fri, Sep 25, 2020 at 03:32:48PM -0500, Eric Blake wrote: > >>+The second is related to exposing the source of various extents within > >>+the image, with a single context named: > >>+ > >>+ qemu:allocation-depth > >>+ > >>+In the allocation depth context, bits 0 and 1 form a tri-state value: > >>+ > >>+ bits 0-1 clear: NBD_STATE_DEPTH_UNALLOC, means the extent is > >>unallocated > >>+ bit 0 set: NBD_STATE_DEPTH_LOCAL, the extent is allocated in this image > >>+ bit 1 set: NBD_STATE_DEPTH_BACKING, the extent is inherited from a > >>+ backing layer > > > >>From the cover description I imagined it would show the actual depth, ie: > > > > top -> backing -> backing -> backing > > depth: 1 2 3 .... (0 = unallocated) > > > >I wonder if that is possible? (Perhaps there's something I don't > >understand here.) > > The real reason I don't want to do a straight depth number is that > 'qemu-img map' combined with x-dirty-bitmap is still a very > convenient way to get at bits 0 and 1 (even if it requires > decoding). But if we plumb in a way for bdrv_get_status to return > depth counts (rather than reimplementing the depth count ourselves), > I would have no problem with returning a struct: > > bits 31-4: the depth of the chain > bits 3-2: reserved (to make reading hex values easier...) > bits 1-0: tri-state of unalloc, local, or backing > > where it would look like: > > 0x0000 -> unallocated > 0x0011 -> depth 1, local > 0x0022 -> depth 2, from the first backing layer > 0x0032 -> depth 3, from the second backing layer > 0x0042 ...
This looks nice too. However I was only bikeshedding so if any of this is hard to do then don't worry too much. Would like to add support for this map to nbdinfo too :-) Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v