Re: [Xen-devel][RFC] Dynamic modes support for PV xenfb (included)

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> The attached files allow the PV framebuffer to be dynamically resized from
> 800x600 to 1024x768 and back.
>
> xen-fbfront-resize.patch is applied to tip of linux-2.6.18-xen
> xen-fbback-resize.patch is applied to tip of unstable-xen

> I am NOT requesting commit to xen- unstable. This is just a posting
> for code review  and feedback.
>
> After the patches  are applied to dom0 and your domU
> PV guest you will need to properly configure the domU X
> server for display modes 800x600 and 1024x768.

Nice.

I took a quite look through the code and was impressed by how small a patch 
was actually required.

A few general comments:
1) I think it would be preferable to be able to dynamically size the memory 
allocated to the framebuffer according to the resolution, rather than 
statically allocating it and then potentially not using all of it.  
Presumably this would require more extensive changes to the backend, since it 
would need to map and unmap the framebuffer memory during a resize operation.  
How complicated do you think this would be?

2) Dynamically allocating the memory would make it practical to support a 
larger range of resultions than currently possible, without wasting lots of 
memory for potential higher resolutions (e.g. to suit users with very big 
monitors connected to dom0).

I think that this is nice support to have available.  Other VMM user 
interfaces even allow resizing of the guest display resolution simply by 
resizing the viewer window on the host - this would require a little more 
software running in the guest to support it but would be cool to support.  Of 
course, that's just me getting excited - simply supporting resize from within 
the guest is a major win in practicality.

Do you have any further plans for xenfb?  It's not got as much love as it 
could have done and it definitely seems like there are things that can be 
done to improve it still further.

Cheers,
Mark

> For testing I used "xrandr" to dynamically resize the domU
> GUI session.
>
> >$ xrandr       // show capabilities
>
>  SZ:    Pixels          Physical       Refresh
>  *0   1024 x 768    ( 361mm x 291mm )  *73
>   1    800 x 600    ( 361mm x 291mm )   73
>   Current rotation - normal
>   Current reflection - none
>   Rotations possible - normal
>   Reflections possible - none
>
> >$ xrandr --size 800x600     //change to 800x600
> >$ xrandr --size 1024x768
>
> domU xorg.conf :
>  SuSE sax2 is not able to configure a PV framebuffer properly
>  so I hand crafted a new xorg.conf file for the PV guest. Below
>  are the sections I changed.
>
> Section "Monitor"
>   HorizSync    30-65
>   Identifier   "Monitor[0]"
>   ModelName    "XEN PVFB"
>   Option       "DPMS"
>   VendorName   "XEN"
>   VertRefresh  43-75
>   UseModes     "Modes[0]"
> EndSection
>
> Section "Modes"
>   Identifier   "Modes[0]"
>   Modeline  "1024x768" 77.25 1024 1080 1192 1360 768 769 772 800
>   Modeline  "800x600" 46.15 800 840 920 1040 600 601 604 625
> EndSection
>
> Section "Screen"
>   SubSection "Display"
>     Depth      24
>     Modes      "1024x768" "800x600"
>   EndSubSection
>   Device       "Device[0]"
>   Identifier   "Screen[0]"
>   Monitor      "Monitor[0]"
> EndSection
>
> Pat



-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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