Re: [Qemu-devel] [RfC PATCH 0/5] console: qom-ify & extent screendump monitor command

[Luiz Capitulino <lcapitulino@redhat.com>]

On Thu, 18 Apr 2013 06:10:19 -0600
Eric Blake <eblake@redhat.com> wrote:

> On 04/18/2013 03:01 AM, Gerd Hoffmann wrote:
> >   Hi,
> > 
> > This patch qom-ifies the QemuConsoles and adds an new, optional
> > parameter to the screendump command to specify the device you
> > want dump from.
> > 
> > Question for the QOM guys: where in the tree should the QemuConsoles
> > show up?  I can't find anything in the tree doing this.  I've placed
> > them below /backend.  See patch #2.  Ok?  Better suggestions?
> > 
> > Question for the libvirt guys:  Is it ok for libvirt to just extend the
> > existing screendump command?  Can libvirt figure there is a new
> > (optional) parameter?  See patch #5.
> 
> The existing libvirt API is:
> 
> char *
> virDomainScreenshot(virDomainPtr domain,
>                     virStreamPtr stream,
>                     unsigned int screen,
>                     unsigned int flags)
> 
> which uses the screen argument to distinguish both between devices and
> heads on a given device:
> 
>  * The screen ID is the sequential number of screen. In case of multiple
>  * graphics cards, heads are enumerated before devices, e.g. having
>  * two graphics cards, both with four heads, screen ID 5 addresses
>  * the second head on the second card.
> 
> So yes, I think libvirt will be able to drive the new command by knowing
> how many heads appear per device, then passing in the appropriate named
> device to the QMP command.  And yes, I'll review patch 5 regarding
> interface design.

We can extend screendump on HMP, but the general rule for QMP is to add a
new command instead so that clients don't have to play tricks like Eric is
suggesting :)

Is there any big issue with adding a new command?