Re: [libvirt] [Qemu-devel] [PATCH RFC 0/4] Allow hibernation on guests

On Thu, 26 Jan 2012 08:18:03 -0700 Eric Blake<eblake(a)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.