Re: Xen frame buffer related

[Samuel Thibault <samuel.thibault@eu.citrix.com>]

Hello,

Dushmanta Mohapatra, le Thu 03 Apr 2008 09:57:11 -0400, a écrit :
> I see two xenfb.c files in the Xen (3.2) source. One in tools/ioemu/hw/ and the
> other in linux-2.6.18-xen.hg/drivers
> /xen/fbfront/. So I think the first one is the userspace-backend and the second
> one is the kernel-space front-end.

That's it.

> I do not understand why originally the
> back-end was not made a part of kernel like other devices?

Why should it be?  In the case of PVFB, he backend is responsible for
actually showing the frame buffer.  A userspace X11 application or VNC
server is thus the logical way.

> Also could you please tell me how to use this backend userspace tool.

You just need to add

vfb = [ 'type=sdl' ]

if you want to have an SDL window showing up when you start your domain,
or

vfb = [ 'type=vnc' ]

if you want to have a VNC server started instead.

> If I have understood it correctly then in Xen 3.1, this  back end tool  uses
> VNCServer for displaying  the contents  of  Frontend  frambuffer.  So what has
> changed with the use of QEMU.

There is now the SDL choice.

> Finally just to give you an idea about my project:  Lets suppose a domU gets
> migrated from a Physical machine having a display of X1xY1 to another physical
> machine having a display of X2xY2.

In the unstable tree, there is an OpenGL rendering which can accomodate
with this by rescaling the frame buffer.

> Also a similar example can be a domU getting migrated from a machine
> having one type of keyboard to a machine having another type of
> keyboard.

Mmm, you may have a problem here, because PVFB uses Linux keycodes, not
keysyms.  I.e. whatever the configuration of the host machine, the guest
keyboard configuration will be used.

> If I see Xen
> 3.2 code in the user space backend framebuffer code (/tools/ioemu/hw/xenfb.c) I
> see functions like "static int xenfb_read_frontend_fb_config(struct xenfb
> *xenfb)" and "static int xenfb_read_frontend_kbd_config(struct xenfb *xenfb)".

That's to get the initial size, but in the unstable tree we now have a
PVFB event that permits the guest to change the size dynamically.

Samuel