Re: [Qemu-devel] RFC v2: blockdev_add & friends, brief rationale, QMP docs

[Avi Kivity]

On 06/15/2010 04:27 PM, Markus Armbruster wrote:
> > I'm only talking about the interface, not the implementation.
> > Internal design details shouldn't be exposed.
> >
> > For the implementation, I imagine you can create an empty blockdev
> > during guest device creation and treat blockdev_add/blockdev_del as
> > media change/eject.
> >      
> If blockdev_del only ejects media, then we need another command to get
> rid of a blockdev.
>    

No.  If you have a blockdev just to satisfy the guest device's need for 
a blockdev pointer, you can delete it automatically when the last 
reference goes.


> Unless you propose that blockdev_del merely ejects media if the blockdev
> is being used by a device, but destroys the blockdev outright if not.
> But that would be sick, wouldn't it?
>    

Create a blockdev implicitly with guest device creation, and use 
blockdev_add (or media_attach) to attach the media.

(but that creates a window where the guest device is visible but media 
is not yet inserted?)

> > > > To pretend you're a media changer, blockdev_add all your cds at once
> > > > and just change the guest/host association when you want to hear a new
> > > > band.
> > > >
> > > > For a fake a multipath setup, blockdev_add one device, associate it
> > > > with multiple guest interfaces.
> > > >
> > > > Otherwise, looks good.
> > > >
> > > >          
> > > Any preference on the command line option syntax?
> > >
> > >        
> > Something incredibly long and complicated?
> >
> > We might keep the existing stuff which is already complicated enough
> > for users, and ask machines to build guests using QMP instead of the
> > command line.
> >      
> I sketched three ways to do -blockdev.  They attempt to make the simple
> simple, and the complex possible.  Any preference among them?
>
>    

I'll look again.

> We can't simply keep -drive, because of the flaws I listed in the
> rationale.
>    

Ok.

--
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