[libvirt] [PATCH 8/9] qemu: capabilities: Lock out incremental backup capability without blockdev

[Peter Krempa]

On Tue, Nov 26, 2019 at 14:57:25 -0500, Cole Robinson wrote:
> On 11/25/19 7:53 AM, Peter Krempa wrote:
> > Blockdev is required to do incremental backups properly. Add a helper
> > function for locking out capabilities and export it to allow re-doing
> > the processing if a different code path modifies capabilities.
> > 
> > Signed-off-by: Peter Krempa <pkrempa at redhat.com>
> > ---
> >  src/qemu/qemu_capabilities.c | 17 +++++++++++++++++
> >  src/qemu/qemu_capabilities.h |  2 ++
> >  2 files changed, 19 insertions(+)
> > 
> 
> Reviewed-by: Cole Robinson <crobinso at redhat.com>
> 
> this made me go look at the case that _BLOCKDEV is disabled. bus='sd',
> hmm that's unfortunate. Do you know if there's qemu plans to make it
> -blockdev compatible? Maybe -machine option like was done with -pflash?
> Or are we stuck with that indefinitely?

There are IIRC 3 board models which don't support sd via -device. Also
there isn't much documentation that would guide us how to use -device
instead of -drive for this. Said that, most boards are already converted
and have e.g. explicit SD controllers, so many cases would be fixable,
but that requires some deep knowledge of qemu.