Re: [Qemu-devel] [RFC PATCH] block: Fix eject -f for locked devices

[Amit Shah <amit.shah@redhat.com>]

On (Fri) 18 Feb 2011 [16:16:07], Markus Armbruster wrote:
> From 8cd4978c9be6ff2bcc414bb1c1b258b96b9a74c1 Mon Sep 17 00:00:00 2001
> From: Markus Armbruster <armbru@redhat.com>
> Date: Fri, 18 Feb 2011 15:54:02 +0100
> 
> After forcefully ejecting media locked by the guest, you can't ever
> again insert new media.
> 
> Example:
> 
>     (qemu) info block
>     hda: type=hd removable=0 file=test.img ro=0 drv=raw encrypted=0
>     cd: type=cdrom removable=1 locked=1 file=x.iso ro=0 drv=raw encrypted=0
>     (qemu) eject cd
>     Device 'cd' is locked
>     (qemu) eject -f cd
>     (qemu) info block
>     hda: type=hd removable=0 file=test.img ro=0 drv=raw encrypted=0
>     cd: type=cdrom removable=1 locked=1 [not inserted]
>     (qemu) change cd x.iso
>     Device 'cd' is locked
> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
> I'm not entirely sure this is the appropriate fix, and that's why
> there's RFC in the subject.
> 
> Both IDE and SCSI devices expose their drive's BlockDriverState member
> locked to the guest via mode sense.
> 
> What does real hardware do when I force-eject media (typically by
> rummaging in that little hole with a paperclip)?  Does it actively
> notify the OS?  Does mode sense change?

I think this should happen.  Calling the 'change_cb' with a new
CHANGE_EJECT parameter can notify the guest of the medium going from
READY to NO_MEDIUM.

The guest can then probe for the status of the tray.

However, I currently don't know if devices are supposed to send such
events to OSes, and how, if they are supposed to.  We currently
approximate this using ide_set_irq() for the cdrom case in
cdrom_change_cb().

This patch looks sensible, though.

> A possible alternative fix is to make do_change_block() ignore
> bdrv_is_locked() when inserting media into an empty drive.
> 
>  block.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/block.c b/block.c
> index b476479..295cf7b 100644
> --- a/block.c
> +++ b/block.c
> @@ -682,6 +682,7 @@ void bdrv_close(BlockDriverState *bs)
>          }
>  
>          /* call the change callback */
> +        bs->locked = 0;
>          bs->media_changed = 1;
>          if (bs->change_cb)
>              bs->change_cb(bs->change_opaque, CHANGE_MEDIA);

		Amit