yes, I got your point, thanks very much Eric. If I want to take a distributed snapshot, which need pause all the VMs and then take snapshot, how can I control the pause for all the VMs? Is there only way that I turn to freeze/thaw functions? and freeze/thaw only for file systems, not for the whole guest, am I right? Thanks a lot! Best, Yuanzhen On Wed, Aug 6, 2014 at 11:35 AM, Eric Blake <eblake@redhat.com> wrote:
On 08/06/2014 08:36 AM, Yuanzhen Gu wrote:
[please don't top-post on technical lists]
Thanks very much Eric! This is exactly what I guessed, I just wondering where I could find this piece of code and control the the pause time of guest, while the snapshot being taken? thanks !
Actually, for new enough qemu (one with the 'transaction' QMP command), or for a guest where only one disk is being snapshotted, there is no pause required. See qemuDomainSnapshotCreateDiskActiveExternal in src/qemu/qemu_driver.c. When a pause is required, it is only for the fraction of a second required to issue a followup qemu QMP command to resume the guest, so there is no need for a knob to control the pause time (it is as already as fast as possible).
-- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org