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Date: Fri, 10 Feb 2012 08:58:17 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC 0/5]: QMP: Introduce GUEST_MEDIUM_EJECT &
	BLOCK_MEDIUM_CHANGED
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To: Markus Armbruster <armbru@redhat.com>
Cc: kwolf@redhat.com, eblake@redhat.com, qemu-devel@nongnu.org, Luiz Capitulino <lcapitulino@redhat.com>

On 02/09/2012 04:01 PM, Markus Armbruster wrote:
> Your GUEST_MEDIUM_EJECTED does*not*  track my open<->  closed.  I think
> it's more complex than a straight open<->  closed event.  Evidence: your
> event documentation in qmp-events.txt needs an extra note to clarify
> when exactly the event is emitted.

I think I agree at this point that always generating an event for open 
<-> closed would make sense.

However, we need to write a proper state machine rather than keeping it 
implicit.  Events would be generated in the state machine rather than 
magically in bdrv_eject/bdrv_close.  We could also take the occasion to 
move all this out of block.c which is becoming huge.  So we would have:

guest eject, tray locked:
     nothing

guest eject, tray unlocked:
     BLOCK_MEDIUM_EJECT
     empty/full not affected

guest eject, tray open:
     BLOCK_MEDIUM_EJECT
     empty/full not affected

eject, tray locked:
     eject request sent to guest
     guest responds to eject request as above

eject, tray unlocked and full:
     BLOCK_MEDIUM_EJECT
     BLOCK_MEDIUM_CHANGED

eject, tray unlocked and empty:
     BLOCK_MEDIUM_EJECT

eject, tray open and full:
     BLOCK_MEDIUM_CHANGED

eject, tray open and empty:
     no event

change, tray locked:
     eject request sent to guest
     guest responds to eject request as above

change, tray unlocked and full:
     BLOCK_MEDIUM_EJECT (to open)
     BLOCK_MEDIUM_CHANGED (perhaps twice? full -> empty -> full)
     BLOCK_MEDIUM_EJECT (to close)

change, tray unlocked and empty:
     BLOCK_MEDIUM_EJECT (to open)
     BLOCK_MEDIUM_CHANGED
     BLOCK_MEDIUM_EJECT (to close)

change, tray open and full:
     BLOCK_MEDIUM_CHANGED (perhaps twice?)
     BLOCK_MEDIUM_EJECT (to close)

change, tray open and empty:
     BLOCK_MEDIUM_CHANGED
     BLOCK_MEDIUM_EJECT (to close)

Luiz, can you try making a proof of concept of this state machine? 
Events then would hopefully come natural.

Paolo