On 12/8/20 4:20 PM, Peter Krempa wrote:
On Tue, Dec 08, 2020 at 16:09:07 +0100, Michal Privoznik wrote:
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@xxxxxxxxxx>
---
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.
Oh, this is actually what we do and it's required! Old libvirt might
have configured the device in a way which is not compatible with the new
one and thus attempting to talk to it using the new interface would just
break.
We currently store the old state of 'qemuCaps' and everything uses it in
the state when the VM was started. Well except for the validator, which
was broken and this patchset is fixing it.
You will never get new features with an old VM.
Okay then.
Michal
