Il 28/01/2013 14:36, Michael S. Tsirkin ha scritto: > On Mon, Jan 28, 2013 at 02:29:23PM +0100, Paolo Bonzini wrote: >> Il 28/01/2013 14:11, Michael S. Tsirkin ha scritto: >>>> I asked for a standalone device because the configuration mechanism >>>> (configfs vs. command-line) and the feature set are completely >>>> different. Unlike virtio-net, it's not possible to switch one to the >>>> other at run time. >>> >>> Exactly the same applies to any other frontend option. >>> For example if you have two qemu instances with >>> different num_queues values you can not migrate one >>> to the other. >>> So in this sense it is not different from any other >>> frontend option, right? >> >> Indeed, in this sense it is not. >> >> Actually in this case migrating one to the other could succeed, and make >> all disks disappear on the destination (because of the different >> configuration mechanism). That however could be overcome with vhost=on >> registering a migration blocker. > > Or better add a subsection if vhost is set: vhost=on to vhost=on > can migrate, right? I think it's not yet supported by the kernel. You have no guarantee that I/O is quiescent at the time the VM starts on the destination. You'd need a ioctl to do the equivalent of bdrv_drain_all(). Once you have that, a subsection would do the job, yes. Paolo >> I won't really block the patch with the vhost=on/off frontend option if >> it is properly done (e.g. the QEMU SCSI bus should not be created for >> vhost=on) and minimally invasive to the non-vhost code. >> >> Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
