Re: [Qemu-devel] block bug: tray status is not updated (and/or guest ignores it)

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri, 27 May 2011 18:10:08 +0530
Amit Shah <amit.shah@redhat.com> wrote:

> On (Fri) 27 May 2011 [17:04:30], Amit Shah wrote:
> > On (Fri) 27 May 2011 [17:01:35], Amit Shah wrote:
> > > On (Thu) 26 May 2011 [15:29:29], Luiz Capitulino wrote:
> > > > 
> > > > I'm testing with qemu.git (HEAD aa29141d84d), procedure:
> > > > 
> > > > 1. Start a VM with:
> > > > 
> > > >  # qemu -hda disks/test.img -enable-kvm -m 1G -cdrom Fedora-14-x86_64-DVD.iso
> > > > 
> > > > 2. Then inside the guest run:
> > > > 
> > > >  # eject /dev/sr0 && mount /dev/sr0 /mnt
> > > > 
> > > > Results:
> > > > 
> > > >  Actual: The cdrom is successfully mounted
> > > >  Expected: The cdrom is not mounted (mount fails, medium not found)
> > > 
> > > Really?  That's what you expect? :-)

That was the VM behavior before 996faf1ad, therefore it's what I was
expecting.

> > > Where will the medium go?

We were leaking it then?

> > > What happens is mount auto-closes the tray and mounts whatever is
> > > there, which is the image you provided.  Works as expected, IMO.
> 
> Confirmed, that's what happens.

Ok. I got this by testing my series that adds the BLOCK_MEDIA_EJECT event.
At first I thought your commit wasn't handling the tray status correctly
(which would cause problems to the new event), but it seems to work fine,
specially now that I know what's doing. Sorry for the noise.

> What's weird though is 'eject' in the monitor makes the cdrom go away
> -- a subsequent mount in the guest results in a no medium error.  I
> thought we had solved that, Markus?
> 
> By not doing a bdrv_close() in the do_eject()->eject_device() call
> path this starts working as expected.

Yes, also note that with the -f option eject is capable of purging
any block device. I wonder if libvirt (or any client) relies on this.

IMHO, we should do the following:

 1. Drop bdrv_close() from eject and change it to just eject a device
    (which also means working only on removable media)

 2. If we really want to be able to remove block devices from the VM,
    we should add a new command for that

 3. The change command does an eject followed by a bdrv_close(), this is
    fine, considering we can't break compatibility here