Re: [PATCH 4/4] qemu: validate: Prefer existing qemuCaps
On 12/8/20 3:01 PM, Peter Krempa wrote:
The validation callback always fetched a fresh copy of
'qemuCaps' to use
for validation which is wrong in cases when the VM is already running,
such as device hotplug. The newly-fetched qemuCaps may contain flags
which weren't originally in use when starting the VM e.g. on a libvirtd
upgrade.
Since the post-parse/validation machinery has a per-run 'parseOpaque'
field filled with qemuCaps of the actual process we can reuse the caps
in cases when we get them.
The code still fetches a fresh copy if parseOpaque doesn't have a
per-run copy to preserve existing functionality.
Signed-off-by: Peter Krempa <pkrempa(a)redhat.com>
---
src/qemu/qemu_validate.c | 30 ++++++++++++++++++++----------
1 file changed, 20 insertions(+), 10 deletions(-)
So this will use the old qemuCaps even though a feature might already be
available in qemu but libvirt didn't detect it. For instance the
virtio-pmem I'm implementing - guests started today won't have the
qemuCap for virtio-pmem because it's not implemented yet. But when they
update libvirt they still won't get the feature because we're using old
qemuCaps for validation and thus new memory model will be denied because
of lacking capability.
I can see the value in when we have to chose between old and new style
of doing things, but I worry it will kill new features.
Michal