[libvirt] [PATCH] snapshot: detect when qemu lacks disk-snapshot support

[Eric Blake]

On 10/18/2011 03:51 PM, Eric Blake wrote:
> Noticed when testing new libvirt against old qemu that lacked the
> snapshot_blkdev HMP command.  Libvirt was mistakenly treating the
> command as successful, and re-writing the domain XML to use the
> just-created 0-byte file, rendering the domain broken on restart.
>
> * src/qemu/qemu_monitor_text.c (qemuMonitorTextDiskSnapshot):
> Notice another possible error message.
> ---
>   src/qemu/qemu_monitor_text.c |    3 ++-
>   1 files changed, 2 insertions(+), 1 deletions(-)

Phooey - testing reveals that this fixes the main problem (the command 
now fails with a nice error without corrupting the domain xml:

# virsh snapshot-create --disk-only dom
error: operation failed: Failed to take snapshot: unknown command: 
'snapshot_blkdev'

), but isn't quite perfect (the 0-byte file is still left behind).  v2 
coming up soon.

-- 
Eric Blake   eblake at redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org