Re: [Xen-users] VNC console access in paravirtualized domUs

[Paul Schulze <avlex@xxxxxxx>]

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Am 21.06.2008 um 01:19 schrieb jim burns

> On Friday June 20 2008 07:09:14 am Paul Schulze wrote:
> > For a 2.6.25 kernel that is be true, but he said he is using Hardy
> > and I think he is using the same kernel for his Hardy DomU as me.
> > That being said, the standard Hardy Dom0/U kernel is version 2.6.24
> > with the Xen components ported from RedHat/Fedora kernel 2.6.22 or 23
> > (as far as I remember), so it is still the old XEN_FRAMEBUFFER=y he
> > has to look out for.
> Heh - I always wondered whether Hardy built on top of the 2.6.24  
> pvops work,
> or they forward ported Xen/Redhat code. That clears that up :-)  
> Still, that
> just means that Hardy is closer in function to the F8 2.6.21 kernel- 
> xen,
> instead of the F9 2.6.25. Either way, Xorg 7.3 acts the same way on  
> both
> systems. On my former F8 domu (& now F9), I had/have a desktop in  
> vnc, but I
> could always Ctrl-Alt-1 to a console, if I so desired. (Actually,  
> virt-viewer
> makes that real easy, altho' it's possible with Fedora vnc.) In  
> fact, setting
> initdefault to 3 in /etc/inittab does away with the desktop  
> altogether. (I
> tend to do init 3/init 5 in my F9 domu to test xorg.conf changes,  
> since it is
> easier than trying to get Tightvnc to send Ctrl-Alt-Backspace ;-),  
> and vnc
> never quits.)
Well, I can't tell you how Xen VNC ought to work, because I've never  
seen it work correctly, except for when I'm running my Xorg session.  
However, I wouldn't use init to restart X for testing. Assuming you  
are using a graphical login manager (xdm/gdm/kdm), you're probably  
better off just restarting that (like /etc/init.d/gdm restart or  
something, no clue if this works the same way on Fedora systems as it  
does on Debian based ones).
> > However, I can say this much, as long as Xorg is not running, it
> > won't have any effect on the framebuffer. The problem here is simply
> > to tell the kernel to use XenFB for its output,
> (Aside - does Hardy use xen-vncfb (typical for xen 3.1.0 or lower)
> or 'qemu-dm -M xenpv ...' (typical for xen 3.1.2 or higher) as the  
> dom0 vnc
> server?)
I would say that depends. In Hardy you actually have two choices for  
the Xen installation, 3.1(.0) or 3.2(.0). I am using 3.2 and it uses  
qemu-dm for VNC, though I imagine 3.1 is still using xen-vncfb. So  
there is also the possibility of Xorg working correctly with Xen 3.1,  
since xen-vncfb might not suffer from the same problem with the  
pixclock, which, as I recall, has something to do with the monitor  
connection/detection. Setting it to 0 like qemu-dm or xenfb (no clue  
which one is responsible) seems to be a bad choice even if it is the  
logical one in this case). Lets hope this will be taken into  
consideration in the future development of applications, relying on  
framebuffer, or the responsible component.
> > though there is the
> > possibility that the same problem occurs with the kernel output
> > module as does with Xorg and therefor the kernel refuses to use the
> > framebuffer. In that case, the solution is not that simple, it would
> > need some kernel debugging since there doesn't seem to be a patch
> > yet.
> I hope not! It seems strange that I've only seen a handful of  
> complainers
> about Hardy vnc support this year. Do Hardy-ers not use vnc, or  
> does it work
> for most of them?
That's actually not strange at all, if you consider some things:  
Virtualization of Linux is mainly used for servers, which in general  
don't need VNC access and in my opinion are better off with just SSH  
access anyways. There are some exceptions to this, like a single VM  
out of the 6, I am currently running, that actually has some use for  
graphical output. I use this VM to run an IRC client, kind of like a  
message box and some custom X-Chat scripts for a channel. But that's  
a pretty unusual thing to do, so not many people will resort to it.  
Secondly, if you run a HVM, VNC should work just fine (and no, I  
haven't tried, because currently, I just don't need HVM  
virtualization for anything). And thirdly, Ubuntu is not all that  
popular for server application. Add all that up and you get like a  
hand full of people that this problem really concerns. I really doubt  
it works out of the box for other Hardy users, with the Xorg package  
in its current state and all (though I am not quiet sure about it).  
But I don't think you should be worried too much, seeing as you use  
Fedora anyways. To me, it sounds like those problems were fixed or  
never occurred in in their packages anyways.

Paul.

- --
Paul Schulze
avlex@xxxxxxx
Public Key: http://solaris-net.dyndns.org/keys/key_avlex.asc

"Making mistakes is human,
but to really fuck things up you need Computers"
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