Re: [Qemu-devel] [PATCH] qmp: add BLOCK_MEDIUM_EJECT event

[Paolo Bonzini]

On 01/27/2012 10:52 AM, Kevin Wolf wrote:
> > >  Conclusion: eject returned an error, but a few seconds later the tray opened 
> > and
> > >               the media wasn't purged. What happened here is that, the_guest_
> > >               opened the tray. The code in this patch would trigger the 
> > event, but
> > >               we shouldn't emit it twice if we cover eject&  change (ie. 
> > special case)
> bdrv_dev_change_media_cb is not called because media cannot be ejected
> with a locked drive. Instead bdrv_dev_eject_request is called which
> doesn't emit an event.
>
> If the guest happens to initiate an eject itself after receiving the
> eject request, it calls bdrv_eject, where we can emit an event.
>
> If we had force=true in the initial eject command, bdrv_close is called,
> which in turn goes through bdrv_dev_change_media_cb where an event is
> emitted.

But we still emit the eject request, and the guest will cause bdrv_eject 
to raise the event again.

There can always be a race with the guest setting the locked bit, so 
management has to do a query-block anyway after eject or change.  That's 
why the event is not necessary when the eject is host-initiated.

Paolo