Re: [Qemu-devel] Close the BlockDriverState when guest eject the media

[Kevin Wolf]

Am 20.10.2014 um 13:27 hat Weidong Huang geschrieben:
> On 2014/10/20 17:41, Kevin Wolf wrote:
> 
> > Am 18.10.2014 um 12:02 hat Weidong Huang geschrieben:
> >> Hi ALL:
> >>
> >> There are two ways to eject the cdrom tray. One is by the eject's qmp 
> >> commmand(eject_device).
> >> The another one is by the guest(bdrv_eject). They have different results.
> > 
> > Yes, they are different things.
> > 
> > If a guest opens the tray (using bdrv_eject) and then closes it again,
> > with no user interaction in between, the virtual media must still be in
> > the drive and the guest must be able to access the same image again.
> > Calling bdrv_close() in this case would be a bug.
> > 
> > The goal of the monitor command "eject" on the other hand is to remove
> > the medium so that the drive is empty. That a device with a closed tray
> > has to be opened for this is only secondary.
> 
> 
> Thanks for your reply.
> 
> There is a problem.
> 
> 1. Qemu receive the "eject" command.
> 2. Runs "eject_request_cb" when an eject request is issued from the monitor, 
> the tray
> is closed, and the medium is locked. But the drive is not closed.
> 3. Guest agree with opening tray and qemu will call bdrv_eject to complete. 
> The drive is
> still not close.
> 
> So the result of the monitor command "eject" is not to remove the medium in 
> this situation.

Now I understand, thanks for explaining.

But I think libvirt can actually work correctly with what qemu offers
today. qemu returns an error if the medium cannot be removed with the
'eject' command and it only sends an eject request to the guest.

With this error, libvirt can know that the DEVICE_TRAY_MOVED event
doesn't mean that the medium has removed, but that it needs to issue
another 'eject' command.

If this isn't implemented correctly in libvirt today, this needs a
libvirt fix rather than a qemu one.

> >> eject_device: close the BlockDriverState(bdrv_close(bs))
> >> bdrv_eject: don't close the BlockDriverState,
> >>
> >> This is ambiguous. So libvirt can't handle some situations.
> >>
> >> libvirt send eject qmp command ---> qemu send eject request to guest --->
> >> guest respond to qemu ---> qemu emit tray_open event to libvirt --->
> >> libvirt will not send change qmp command if media source is null. So
> >> the media is not be replace to the null.
> > 
> > What is the problem that libvirt has with the guest opening the tray? I
> > don't think libvirt should even care about that case.
> 
> 
> For example, using libvirt to change media by xml below(media source is null):
> <disk type='file' device='cdrom'>
>     <driver name='qemu'/>
>     <target dev='hdb' bus='ide'/>
> </disk>
> 
> libivrt return ok. But media still is in the guest.
> This is confused.

Kevin