On Tue, Sep 21, 2010 at 09:58:14AM +0100, Daniel P. Berrange wrote: > On Mon, Sep 20, 2010 at 09:37:16PM +0200, Michael S. Tsirkin wrote: > > On Mon, Sep 20, 2010 at 02:22:18PM -0500, Anthony Liguori wrote: > > > On 09/20/2010 01:59 PM, Michael S. Tsirkin wrote: > > > >>You can also initiate the unplug from the OS without the ACPI event > > > >>ever happening. I suspect that in our current implementation, that > > > >>means that we'll automatically delete the device which may have > > > >>strange effects on management tools. > > > >> > > > >>So it probably makes sense for our interface to present the same > > > >>procedure. What do you think? > > > >> > > > >>Regards, > > > >> > > > >>Anthony Liguori > > > >We seem to have two discussions here. you speak about how an ideal hot > > > >plug > > > >interface will look. This can involve new commands etc. > > > >I speak about fixing existing ones so qemu and/or guest won't crash. > > > > > > To be fair, existing qemu won't crash if you do: > > > > > > (qemu) device_del <device> > > > Use info_qtree to notice when device goes away > > > (qemu) netdev_del <backend> > > > > Asking libvirt to busy loop polling the monitor sounds like a really bad > > situation: note that guest is blocked from doing any io while monitor is > > used, so it may in fact prevent it from making progress. Right? > > Clearly we need either an async command completion, or an async > event notification of device_del. No one wants todo polling, > nor does anyone sane want to try to parse the outout of info > qtree :-) > > > > So why can't we let management do netdev_del and have it take effect > > when this becomes possible? > > That would be really unpleasant to deal with. netdev_del should > always kill the backend immediately, even if the frontend device > still exists. If this could cause issues for the frontend, then just > connect it to a no-op backend internally so it gets no further data. > In the context of drive_del, once it returns, libvirt changes the security > labelling, so QEMU is guarenteed not to be able to use the backend > anymore, even if it tries to. We would do the same for netdev_del if > we could.
OK, that's clear enough. One note though: you won't be able to create another backend with the same name until the frontend is gone. -- MST
