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

[Weidong Huang]

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.

> 
>> 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.

Thanks.

> 
> Kevin
> 
>> So close the BlockDriverState in bdrv_eject. Thanks.
>>
>> diff --git a/block.c b/block.c
>> index d3aebeb..0be69de 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -5276,6 +5276,10 @@ void bdrv_eject(BlockDriverState *bs, bool eject_flag)
>>          qapi_event_send_device_tray_moved(bdrv_get_device_name(bs),
>>                                            eject_flag, &error_abort);
>>      }
>> +
>> +    if (eject_flag) {
>> +        bdrv_close(bs);
>> +    }
>>  }
>>
> 
> .
>