[PATCH for 7.10] qemu: monitor: Fix usage of 'query-blockstats'

[Erik Skultety]

On Thu, Nov 25, 2021 at 01:19:57PM +0100, Peter Krempa wrote:
> Commit bc24810c2cab modified code querying blockstats to use the
> 'query-nodes' parameter so that we can fetch stats also for images which
> are not attached to a frontend such as block copy and backup scratch
> images.
> 
> Unfortunately that broke the old blockstats because if 'query-nodes' is
> enabled qemu doesn't output the 'qdev' parameter which our code used for
> matching to the disk and also qemu neglects to populate the frontend
> stats at all so we can't even switch to using nodenema for matching.
> 
> To fix this we need to do two calls, one with 'query-nodes' disabled
> using the old logic to populate everything and then an aditional one
> which populates all the remaining images.
> 
> Closes: https://gitlab.com/libvirt/libvirt/-/issues/246
> Signed-off-by: Peter Krempa <pkrempa at redhat.com>
> ---

Tested-by: Erik Skultety <eskultet at redhat.com>