Re: [libvirt] Close the BlockDriverState when guest eject the media
On 2014/10/20 19:39, Kevin Wolf wrote:
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.
hi all! How about fix it in libvirt?
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
.
On 2014/10/21 13:53, Weidong Huang wrote:
On 2014/10/20 19:39, Kevin Wolf wrote:
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.
hi all!
How about fix it in libvirt?
Cc'ing Eric for more attention. Maybe He can give you some suggestion :) Best regards, -Gonglei
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
.
On 10/21/2014 12:10 AM, Gonglei wrote:
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.
This whole area of interaction is messy, and this is not the first time someone has tried to improve it. Is qemu actually issuing an error message in this case, and is it distinguishable from other errors?
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.
Yes, patching libvirt to recognize this situation and try a second time to remove the disk from the tray once the guest has opened the try, in order to completely close out the drive, makes sense.
hi all!
How about fix it in libvirt?
Cc'ing Eric for more attention.
Maybe He can give you some suggestion :)
At this point, it may be best to make sure there is a bugzilla entry against libvirt, to make sure it is not forgotten. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
Eric Blake <eblake@redhat.com> writes:
On 10/21/2014 12:10 AM, Gonglei wrote:
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.
This whole area of interaction is messy, and this is not the first time someone has tried to improve it. Is qemu actually issuing an error message in this case, and is it distinguishable from other errors?
0. Guest has a medium the guest locked into its CD-ROM drive: (qemu) info block cd cd: r7.iso (raw, read-only) Removable device: locked, tray closed Using HMP because QMP's query-block dumps a lot of detail on us that isn't relevant here. 1. eject it { "execute": "eject", "arguments": { "device": "cd" } } Fails, but notifies guest: {"error": {"class": "GenericError", "desc": "Device 'cd' is locked"}} Tray stayed put: cd: r7.iso (raw, read-only) Removable device: locked, tray closed Guest reacts to the notification and duly ejects: {"timestamp": {"seconds": 1414396646, "microseconds": 494175}, "event": "DEVICE_TRAY_MOVED", "data": {"device": "cd", "tray-open": true}} Tray is now open: cd: r7.iso (raw, read-only) Removable device: not locked, tray open I actually stopped the guest around the eject command to reliably capture tray status between eject and the guest's reaction. 2. eject it again { "execute": "eject", "arguments": { "device": "cd" } } {"return": {}} Medium is now gone: cd: [not inserted] Removable device: not locked, tray open The first eject fails with GenericError, same as other errors such as "Device '%s' is not removable". I feel reporting an error in the "locked" case is actually inappropriate, because asking the guest is exactly what the command is supposed to do then. I doubt we can change the existing commands, but we can do better in the new QMP commands I mentioned upthread. I figure a new command should return a value to distinguish the two success cases "I opened the tray" and "I asked the guest to open the tray". Until such new commands are available, I'm afraid all you can do is keying on event DEVICE_TRAY_MOVED. [...]
participants (4)
-
Eric Blake -
Gonglei -
Markus Armbruster -
Weidong Huang