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Re: [libvirt] [PATCH 0/2] Introduce two new virsh commands

On 06/29/2011 06:19 AM, Osier Yang wrote:
> These two patches is to introduce two new virsh commands, one is
> eject-media, which is to eject media from CD or floppy drive, the other
> is insert-media, which is to insert media into CD or floppy drive.
> There are commands existed can be used to eject/insert media, such as
> "update-device", but it's not quite easy to use. That's the original
> intention of these patches.
> Both of the two commands only allow to operate on CDROM or floppy disk.
> [PATCH 1/2] virsh: Introduce two new commands to insert or eject media
> [PATCH 2/2] doc: Add docs for two new introduced commands

I think that we will eventually need even more; therefore, I'm thinking
a more generic 'change-disk' command would be better than two specific
'eject-media' and 'insert-media' commands.  Recent qemu added [1]:

 o blockdev-tray-open: opens the drive tray. Also Supports removing the
   media. The BLOCK_TRAY_OPEN event is emitted if this command succeeds.
 o blockdev-tray-close: closes a drive tray. The BLOCK_TRAY_CLOSE event is
 o blockdev-media-insert: Inserts a media in the tray. The tray must empty
   and already opened. No event is emitted.

along with updating to 'eject' and 'change' in terms of these more
fundamental operations.

[1] http://lists.nongnu.org/archive/html/qemu-devel/2011-06/msg00381.html

That is, it should be possible to have libvirt issue a command to tell
the guest's virtual cd tray to open, a command to tell the tray to
close, and a command to tell qemu to change which disk is in the tray
but leaving the tray open, and expose all of these through virsh.

Meanwhile, it should also be possible to register for events to be told
when the guest has initiated a tray open or tray close, although I'm not
quite as sure that events need to be exposed through virsh.

I think all of the new qemu monitor commands can be mapped into the
existing virDomainUpdateDeviceFlags by way of adding a new XML attribute
to the <device>/<disk>/<target> element for guest cdrom devices, as in:

<disk> type='file' device='cdrom'>
  <driver name='qemu' type='raw'/>
  <source file='/path/to/my.iso'/>
  <target dev='hdc' bus=ide' tray='open'/>

I don't think we need any new flags to virDomainUpdateDeviceFlags;
rather, the additional xml attribute tray='open|closed' (omitted element
implies closed) should be sufficient to correctly decide which monitor
command(s) are necessary to get the virtual cdrom into the requested new

Hmm, does qemu have a way at the command line to start a guest with the
tray already open?  If not, that feels like a missing qemu feature.

But from the virsh aspect, it seems like a more generic change-disk is
better than specific eject-media and insert-media commands:

change-disk domain target {--current | [--live] [--config]} [--force]
[{--open | --close}] {--keep | [media]}

Change the state of the virtual cdrom disk <target> within <domain>.
<--current>, <--live>, <--config> behave as usual.
If <--force>, then force the change even if the disk was previously
mounted by the guest.
Either <--open> or <--close> may be specified to change the state of the
virtual tray; if neither is given, the tray will be put back to its
original state (although if it was already closed, the process involves
temporarily opening the tray).
If <--keep> is specified, then <--open> or <--close> only affects tray
state without changing media.  Otherwise, if <media> is specified, the
contents of the tray are changed to the new media, and if <media> is
omitted, then the tray is emptied.


change-disk dom hdc --live /path/to/my.iso
=> checks for existing <disk><target dev='hdc'/></disk> and tray state.
 If tray state is closed, this creates new xml that changes the <source
file='...'/>, and calls virDomainUpdateDeviceFlags with the new XML,
which in turn attempts the 'change' monitor command which tries to open
the tray, swap the media, then close the tray; this will fail if the
guest has mounted the previous media and thus locked the tray.  If tray
state is open, then this maps to the 'blockdev-media-insert' monitor
command that changes the media but leaves the tray open.

change-disk dom hdc --live --force /path/to/my.iso
=> likewise, but with the force flag passed to
virDomainUpdateDeviceFlags, and thus to the 'change' monitor command, so
it should succeed

change-disk dom hdc
=> changes the xml <source> to be empty, effectively removing the media
from the disk

change-disk dom hdc --open --keep
=> changes the xml to request the new tray=open attribute, but leaves
<source> alone, so that the guest could initiate a tray-close action and
see the same .iso that was previously in the disk

change-disk dom hdc --close /path/to/my.iso
=> ensure that the new tray state is closed and contains the new iso,
even if the tray was previously opened

Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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