On 06/24/2014 03:29 PM, Brian Jackson wrote: > > > On 6/24/2014 2:22 PM, Xiongzi Ge wrote: >> Hi, >> >> >> When I do live migration, in the source and destination host, there are >> different block devices, but qemu can not detect this. I used virtio >> as the >> driver in kvm and in the vdi device in the guest is /dev/vda. So, >> the vm >> guest can read different data from the same /dev/vda device. I am >> studying >> this code to let qemu understand that, this is a new device. >> >> Does qemu recognize different block devices after live migration? > > You aren't supposed to have different command line options when live > migrating (with the exception of -incoming if you migrate that way). So > whatever you are trying to do is unsupported.
Caveat - it IS supported to change command line options for things that do NOT impact guest ABI. For example, if you have /path/to/file as the host location containing the guest image on the source, but /other/path/file as the location on the destination, you CAN rewrite that parameter (and in fact, libvirt DOES supporting the rewrite such parameters if you use the 'virsh migrate --xml' option - after first proving that your changes do not affect guest ABI). But the onus is on you to ensure that src:/path/to/file and dst:/other/path/file have the SAME guest-visible contents at the time of the migration (this generally requires that the two names be mappings to the same underlying network resource; you can get trickier, but it starts to be at your peril, because the guest is hosed if the two files differ in guest contents). -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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