Re: [Qemu-devel] [PATCH 6/6] qmp: add balloon-get-memory-stats & event

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

On Fri, Feb 17, 2012 at 10:55:41AM -0600, Anthony Liguori wrote:
> On 02/08/2012 02:30 PM, Luiz Capitulino wrote:
> >This commit adds a QMP API for the guest provided memory statistics
> >(long disabled by commit 07b0403dfc2b2ac179ae5b48105096cc2d03375a).
> >
> >The approach taken by the original commit
> >(625a5befc2e3200b396594f002218d235e375da5) was to extend the
> >query-balloon command. It introduced a severe bug though: query-balloon
> >would hang if the guest didn't respond.
> >
> >The approach taken by this commit is asynchronous and thus avoids
> >any QMP hangs.
> >
> >First, a client has to issue the balloon-get-memory-stats command.
> >That command gets the process started by only sending a request to
> >the guest, it doesn't block. When the memory stats are made available
> >by the guest, they are returned to the client as an QMP event.
> >
> >Signed-off-by: Luiz Capitulino<lcapitulino@redhat.com>
> 
> Do we need this to be stable in 1.1?
> 
> We can do this pretty nicely through QOM.  We can have a polling
> property in the virtio-balloon driver, that when set, will enable
> the virtio-balloon device to poll the guest for statistics.
> 
> We can also have properties for each of the memory statistics and a
> timestamp for when the last update was.
> 
> I think this is a friendlier approach for clients, and a cleaner
> approach from a QEMU perspective.
> 
> There's nothing generic about this functionality.  It's extremely
> specific to virtio-balloon.  We just lacked ways to expose device
> specific function pre-QOM.

I'm not so sure, I think proxying guest agent commands through QMP
would hit very similar snags, for instance.

> 
> Regards,
> 
> Anthony Liguori
> 
>