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

[Michael Roth <mdroth@linux.vnet.ibm.com>]

On 01/26/2012 09:18 AM, Eric Blake 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.

We could drop the state tracking (guest-fsfreeze-status) and issue the 
freeze/thaw unconditionally. Talked with Anthony and going stateless in 
general seems to solve a lot of nastiness that might pop up with the 
current implementation. I'll send some patches out soon for fsfreeze, 
guest-file* may end up getting similar treatment in the 
not-too-distant-future.