[Spice-devel] [PATCH 07/12] block: save the associated child in BlockDriverState

[Marc-André Lureau]

Hi


On Fri, Jun 21, 2013 at 1:57 PM, Paolo Bonzini <pbonzini at redhat.com> wrote:

>
>
> >     What exactly are you trying to do here (I guess I'll understand more
> >     when I get to the later patches)?
> >
> > Getting to the bottom BlockDriverState to be able to eject & change it.
> > (it could also be named the "parent", but other parts of the code
> > suggest the "child" name)
>
> There is already an interface for eject/change, which is the monitor.
> To signal an eject or medium change, the SPICE client should simply ask
> libvirt to do so.  It is fine to change "from" spicebd: "to" spicebd:,
> the guest would still perceive it as a change.
>
> I'm not sure how libvirt communicates the change back to the SPICE
> client, and whether it is asynchronous or synchronous.
>
>
Spice is not using libvirt, and doesn't have access to monitor. I looked at
the monitor code. Basically, the spice block driver I proposed uses a
similar code to forcefully eject and change.

Perhaps it's possible for the Spice qemu-side code to have access to the
monitor, but the end result would be similar anyway.


> BTW, note that IDE or virtio-blk do not support removable media, and are
> not able to pass eject or media change notifications.  SCSI devices
> (such as usb-bot, usb-uas and virtio-scsi) can.
>
> >     Can you draw the relationships between all the BlockDriverStates in a
> >     spicebd: drive?
> >
> >
> > Hopefully, but I have only tested with raw images (w/wo snapshot).
>
> Then draw it. :)  But from the above description it looks like it is not
> necessary, it should simply be "raw" on top of "spicebd".  Parsing
> formats should be done on the client side, perhaps by invoking qemu-nbd
> and tunnelling the NBD data on the SPICE channel.
>
>
Right, "raw" on top of "spicebd" for iso/raw images (and "qcow2" on top for
snapshot support - even in readonly).

I wonder what would happen if spicebd image would be something else than
raw/iso, I suppose there would be more BlockDriverStates to handle the
various format.

-- 
Marc-André Lureau
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