[Qemu-devel] [RFC] Time resync by qemu-ga

[Lei Li <lilei@linux.vnet.ibm.com>]

Hi guys,

I am working on the time drift issue as background info here.

http://mid.gmane.org/87pq5r5otp.fsf@codemonkey.ws

As Anthony proposed, one part of the solutions is that we want
to add a qemu-ga command to resync the guest clock by reading the
wallclock time when the tick overflow the limit to the number
of missed ticks.

When I implement on the qemu-ga side, I got some problems and
I'd like to send this RFC out and ask for suggestions and comments
to make sure I am in the right direction before I send out the code.

The proposed interface for qemu-ga command as link here:

http://wiki.qemu.org/Features/GuestAgent/UsefulCommands

This maybe easier to implement, but I think this interface may
have problem, like the delta issue. So I am trying to implement
it like below.

The interface looks like:

{ 'command': 'guest-resync-time' }

The way it works:

When calling this command in the host, qemu-ga would try to
get the wallclock time in the host by handling guest->host
commands, and then write this time to the guest hardware.

But looks like we don't have the way to get host information
now, since qemu-ga just handle host->guest commands (Correct
me if I am wrong). To solve this, we should add support to
get host information by handling guest->host commands by qemu-ga
first.

Please correct me if I am wrong. And suggestions and comments
are very appreciated, specifically the way to handle quest->host
commands by qemu-ga since I am still struggling with this.

Thanks!

-- 
Lei