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[Xen-users] Re: graphically accessing pv guest

To: "Fajar A. Nugraha" <list@xxxxxxxxx>
Subject: [Xen-users] Re: graphically accessing pv guest
From: Ted Brenner <griztown@xxxxxxxxx>
Date: Mon, 28 Feb 2011 15:59:01 -0600
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Thanks Fajar!  This is a big help.  I tried xrdp but there were a few issues.  If I used tightvncserver it would connect but then crash immediately.  If I used vnc4server, I couldn't connect from dom0 but could from my wife's laptop.  But even when I connected it was very slow.  One thought I had was to use this parameter to pass in more video memory than 4MB hoping that would helping things out.  Perhaps there is a better way to do this?

The other issue I had with this approach is that I was trying to use vpn in the guest.  Once the vpn is connected, the xrdp connection gets dropped.  Perhaps I shouldn't be running vpn in a guest or using VirtualBox instead.  Can you use VirtualBox on a xen server?  Do they play well together?

Thanks again!  I'll test this out tonight and let you know how it works.

On Sun, Feb 27, 2011 at 10:27 PM, Fajar A. Nugraha <list@xxxxxxxxx> wrote:
On Mon, Feb 28, 2011 at 10:15 AM, Ted Brenner <griztown@xxxxxxxxx> wrote:
> Is it possible that in Xen 4.0+, the 'xenfb.video' should be added to the
> kernel line of the /boot/grub/menu.lst file?
> On Sun, Feb 27, 2011 at 10:49 AM, Ted Brenner <griztown@xxxxxxxxx> wrote:
>> Hi all,
>> I'm trying to expand the screen resolution of my guest when using vnc.  It
>> appears I need to use the extra variable in my guest config file and xenfb.
>> I pass it in like this:
>> extra = 'xenfb.video=8,1024,768'
>> I can see this being passed to the kernel when it boots but it doesn't
>> change the vnc screen resolution.

Thanks for pointing out that parameter.

There are three parts answer to your question.

The first part, being how to pass a parameter to kernel. That would
depend on how you boot domU:
- If you use pygrub/pv-grub, then the correct way to pass it would be
to edit domU's grub config file (or some other config file that is
used to generate it, like /etc/default/grub).
- If you use pygrub, you might be able to use "args" to add it without
editing domU's grub config file
- If you use "kernel" and "ramdisk", then the right way to add it is
on "extra" line (which should already contain things like "root=")
You can check with "cat /proc/cmdline" inside domU to see if the
parameter is correctly passed to domU kernel.

The second part is where to put the parameter:
- If xen vfb support is compiled built-in in domU kernel, then the
only place to pass it is on domU kernel command line, using one oh the
three options mentioned above
- If xen vfb support is built as a module, you can pass it on domU
kernel command line, or by simply creating a .conf file on
/etc/modprobe.d (recommended)

The third part is what's the correct module name, and what parameter
to pass. In Ubuntu maverick, the module name is xen-fbfront.
$ modinfo xen-fbfront
alias:          xen:vfb
license:        GPL
description:    Xen virtual framebuffer device frontend
srcversion:     0EB34742ACF8D2559403034
depends:        fb_sys_fops,syscopyarea,sysfillrect,sysimgblt
vermagic:       2.6.35-25-generic SMP mod_unload modversions
parm:           video:Video memory size in MB, width, height in pixels
(default 2,800,600) (array of int)

So considering all three parts, if you use Ubuntu maverick and want to
use 1280x1024, you can just create a file like this:
$ cat /etc/modprobe.d/xen-fbfront.conf
options xen-fbfront video=32,1280,1024

A "depmod -a" and "update-initramfs -u" might be needed afterwards.
After reboot, it should correctly use 1280x1024 resolution.

I still say you should use things like NX/xrdp/vnc server inside domU
though (my favorite is xrdp). It's smooth, easy to install (apt-get
install xrdp), can allow you to choose different resolution without
having to reboot (just specify the desired resolution and color depth
when you connect), and allows you to have multiple GUI session to the
client (using idfferent user-resolution-depth combination)


Ted Brenner
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