[libvirt] [PATCH] Fix macvtap device tear down problem on virsh destroy

[Stefan Berger]

Ed Swierk <eswierk at aristanetworks.com> wrote on 02/15/2010 11:15:11 PM:
> 
> On Mon, Feb 15, 2010 at 4:39 PM, Stefan Berger <stefanb at us.ibm.com> 
wrote:
> > This patch fixes the problem with the tear down of the macvtap device
> > when issuing a 'virsh destroy' by moving the tear down block past the
> > point of killing the Qemu process. It seems necessary to loop at least
> > once in the case of 'virsh destory' since the device seems to be busy
> > for a while after the Qemu process has been killed. This also still
> > properly tears down the macvtap device when the VM is 'virsh 
shutdown'ed
> > or halted from inside.
> 
> I think it's fine to check just once, before replacing an existing
> macvtap interface with a new one, that the existing interface's fd can
> be opened, to avoid stomping on an interface owned by someone else.

This is for the case when the device gets created. In that case I do 
check for someone else 'accidentally' having the same MAC address.

> 
> On shutdown, I think it's safe to assume that an interface whose name,
> macaddr and type matches is in fact the interface it created. I think
> it should just go ahead and delete it without again trying to open the
> fd. Otherwise we end up with such annoying races, e.g. if qemu hangs
> or takes a long time to shut down, you end up leaving the orphaned
> interfaces sitting around as well as the hung qemu process.

This would be for the case that the SIGKILL on the Qemu process didn't 
actually
tear down the process. I was hoping that that would not happen. I guess 
the 
solution is to introduce another function like 
'delMacvtapByAddressNoBusyCheck'
that skips the test that tries to open the tap device. Does this sound
right ?

   Stefan


> 
> --Ed
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