[libvirt] [PATCH] qemu: don't fail update netdev on bridge detach failure

[Laine Stump]

On 12/13/2012 07:44 PM, Eric Blake wrote:
> On 12/13/2012 05:40 PM, Laine Stump wrote:
>> When a network device's bridge connection is changed by
>> virDomainUpdateDevice, libvirt first removes the netdev's tap from its
>> old bridge, then adds it to the new bridge. Sometimes, due to a
>> network being destroyed while a guest device is still attached, the
>> tap may already be "removed" from the old bridge (or the old bridge
>> may not even exist any more); the existing code was needlessly failing
>> the update when this happened, making it impossible to recover from
>> the situation without completely detaching (i.e. removing) the netdev
>> from the guest and re-attaching.
>>
>> Instead of failing the entire operation when removal of the tap from
>> the old bridge fails, this patch changes qemuDomainChangeNetBridge to
>> just log a warning and continue, allowing a reasonable recover from
>> the situation.
>>
>> (you'll appreciate this change if you ever accidentally destroy a
>> network while your guests are still using it).
> Hmm, I think that may have happened to me while testing dnsmasq fixes
> lately, and I probably just chalked it up to user error...

Depends on your definition of user error :-) If you stop and start a
network that has guests attached, the guests will not be reattached to
the bridge. In order to restore proper operation, you'll need to
update-device each network device moving it to a different bridge, then
back to the original.

>> ---
>>  src/qemu/qemu_hotplug.c | 10 ++++++++--
>>  1 file changed, 8 insertions(+), 2 deletions(-)
> Matches the commit message, which makes sense.  ACK.

Pushed. Thanks!