Re: [Qemu-devel] [PATCH 4/4] qmp: add BLOCK_MEDIUM_EJECT event

[Kevin Wolf <kwolf@redhat.com>]

Am 16.02.2012 19:30, schrieb Markus Armbruster:
> Let's figure out how this stuff really works.
> 
> 1. Guest load/eject
> 
> Guest commands load or eject.  Device model updates its state of virtual
> tray (e.g. IDEState member tray_open) unless locked, then calls
> bdrv_eject().
> 
> bdrv_eject() is a no-op except for pass-through backends such as
> host_cdrom.
> 
> Note: device models call bdrv_eject() whether the state changed or not.
> The only use for that I can see is syncing a wayward physical tray to
> the virtual one.  Shouldn't be necessary with Paolo's recent work,
> should it?

The one case that I'm unsure about is migration. I thought we sync the
physical tray with the virtual one then (or at least we discussed it),
but I don't really know what we do today, or even what the right thing
to do is in some cases.

> I figure Luiz's patch works.  But maybe it could be simplified some by
> replacing bdrv_dev_change_media_cb() by a "open/close tray" callback
> that returns whether it moved.  bdrv_dev_change_media_cb() would then
> simply open the tray, emit event if it moved, close the tray, emit event
> if it moved.

Yes, I had the same impression after reading the first few paragraphs of
your analysis (which looks right to me).

Kevin