On 01/26/2012 01:35 PM, Luiz Capitulino wrote:
On Thu, 26 Jan 2012 08:18:03 -0700 Eric Blake<eblake@redhat.com> wrote:
[adding qemu-devel]
On 01/26/2012 07:46 AM, Daniel P. Berrange wrote:
One thing, that you'll probably notice is this 'set-support-level' command. Basically, it tells GA what qemu version is it running on. Ideally, this should be done as soon as GA starts up. However, that cannot be determined from outside world as GA doesn't emit any events yet. Ideally^2 this command should be left out as it should be qemu who tells its own agent this kind of information. Anyway, I was going to call this command in qemuProcess{Startup, Reconnect,Attach}, but it won't work. We need to un-pause guest CPUs so guest can boot and start GA, but that implies returning from qemuProcess*.
So I am setting this just before 'guest-suspend' command, as there is one more thing about GA. It is unable to remember anything upon its restart (GA process). Which has BTW show flaw in our current code with FS freeze& thaw. If we freeze guest FS, and somebody restart GA, the simple FS Thaw will not succeed as GA thinks FS are not frozen. But that's a different cup of tea.
Because of what written above, we need to call set-level on every suspend.
IMHO all this says that the 'set-level' command is a conceptually unfixably broken design& should be killed in QEMU before it turns into an even bigger mess.
Can you elaborate on this? Michal and I talked on irc about making the compatibility level persistent, would that help?
Once we're in a situation where we need to call 'set-level' prior to every single invocation, you might as well just allow the QEMU version number to be passed in directly as an arg to the command you are running directly thus avoiding this horrificness.
Qemu folks, would you care to chime in on this?
Exactly how is the set-level command supposed to work? As I understand it, the goal is that if the guest has qemu-ga 1.1 installed, but is being run by qemu 1.0, then we want to ensure that any guest agent command supported by qemu-ga 1.1 but requiring features of qemu not present in qemu 1.0 will be properly rejected.
Not exactly, the default support of qemu-ga is qemu 1.0. This means that by default qemu-ga will only support qemu 1.0 even when running on qemu 2.0. This way the set-support-level command allows you to specify that qemu 2.0 features are supported.
Version numbers are meaningless. What happens when a bunch of features get backported by RHEL such that qemu-ga 1.0 ends up being a frankenstein version of 2.0? The feature negotiation mechanism we have in QMP is the existence of a command. If we're in a position where we're trying to disable part of a command, it simply means that we should have multiple commands such that we can just remove the disabled part entirely. Regards, Anthony Liguori