Re: [Qemu-devel] Re: KVM call agenda for Oct 19

Avi Kivity
2010-10-19T13:03:59Z

On 10/19/2010 02:58 PM, Dor Laor wrote:
> On 10/19/2010 02:55 PM, Avi Kivity wrote:
>> On 10/19/2010 02:48 PM, Dor Laor wrote:
>>> On 10/19/2010 04:11 AM, Chris Wright wrote:
>>>> * Juan Quintela (quintela@redhat.com) wrote:
>>>>>
>>>>> Please send in any agenda items you are interested in covering.
>>>>
>>>> - 0.13.X -stable handoff
>>>> - 0.14 planning
>>>> - threadlet work
>>>> - virtfs proposals
>>>>
>>>
>>> - Live snapshots
>>> - We were asked to add this feature for external qcow2
>>> images. Will simple approach of fsync + tracking each requested
>>> backing file (it can be per vDisk) and re-open the new image would
>>> be accepted?
>>> - Integration with FS freeze for consistent guest app snapshot
>>> Many apps do not sync their ram state to disk correctly or frequent
>>> enough. Physical world backup software calls fs freeze on xfs and
>>> VSS for windows to make the backup consistent.
>>> In order to integrated this with live snapshots we need a guest
>>> agent to trigger the guest fs freeze.
>>> We can either have qemu communicate with the agent directly through
>>> virtio-serial or have a mgmt daemon use virtio-serial to
>>> communicate with the guest in addition to QMP messages about the
>>> live snapshot state.
>>> Preferences? The first solution complicates qemu while the second
>>> complicates mgmt.
>>
>> Third option, make the freeze path management -> qemu -> virtio-blk ->
>> guest kernel -> file systems. The advantage is that it's easy to
>> associate file systems with a block device this way.
>
> OTH the userspace freeze path already exist and now you create another
> path.

I guess we would still have a userspace daemon; instead of talking to
virtio-serial it talks to virtio-blk. So:

management -> qemu -> virtio-blk -> guest driver -> kernel fs
resolver -> daemon -> apps

Yuck.

> What about FS that span over LVM with multiple drives? IDE/SCSI?

Good points.

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