Re: Dynamic modes in PV xenfb?

[Markus Armbruster <armbru@redhat.com>]

"Pat Campbell" <plc@novell.com> writes:

> Hi,
>
> At http://wiki.xensource.com/xenwiki/VirtualFramebuffer in Stage 2 adding 
> dynamic modes to the Xen VirtualFramebuffer is mentioned.
>
> Does not appear this was ever done.  Is there a technical reason this has not 
> been implemented or just a case of not enough time or interest?
>
> If it is technically feasible do you have any pointers or examples on how to
> go about implementing this feature?
>
> Thanks in advance.
>
> Pat

The protocol between frontend and backend is easy enough to extend in
a backward compatible manner, so negotiating resolution changes
shouldn't be hard.  Guard the extension with suitable flags in
xenstore (feature-FOO to offer FOO, request-FOO to take it, see source
code for examples).

The frontend exposes the framebuffer to the backend in a rather
archaic manner.  The size of the page directory artificially limits
the framebuffer to 4M.  Fixable, but I'd rather see this converted to
grant tables (assuming they can support large grants now).

>From a usability point of view, you should be able to resize the pvfb
window like any other window.  But then the backend initiates the
resize.  I don't know whether software running in the frontend is fine
with framebuffers initiating resolutions changes.

Please let me know if you tackle this feature.