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Re: [Xen-devel] Xen frame buffer related

To: "Dushmanta Mohapatra" <dushmanta.mohapatra@xxxxxxxxx>
Subject: Re: [Xen-devel] Xen frame buffer related
From: Markus Armbruster <armbru@xxxxxxxxxx>
Date: Sat, 05 Apr 2008 10:22:34 +0200
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, samuel.thibault@xxxxxxxxxxxxx
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In-reply-to: <46009afb0804041220s2a9627f4lc62952396b4fb02b@xxxxxxxxxxxxxx> (Dushmanta Mohapatra's message of "Fri\, 4 Apr 2008 15\:20\:48 -0400")
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"Dushmanta Mohapatra" <dushmanta.mohapatra@xxxxxxxxx> writes:

> Thanks for the detailed reply. Makes the things a lot more clearer to me.
> But I have got a few more questions.
> How do I use the VNC/SDL to view domU's console.  I saw a thread
> http://lists.xensource.com/archives/html/xen-devel/2007-08/msg00351.html
> related to this and followed the approach.
> (I assume all the 10 patches mentioned in this series are available in Xen
> 3.2. Am I right?)
> In my domU config file I use options like this;
> vfb = [ 'type=sdl' ]
> #vfb = ['type=vnc ']
> #extra = "xencons=tty video=xenfb"
> extra = 'xencons=ttyS0 console=ttyS0 video=xenfb'

I've never tried video=xenfb, no idea what it does.  I prefer to
compile both xenfb and xenkbd in (not module).

I don't use any extra kernel arguments.  But I use Fedora kernels and
upstream kernels, not unpatched 2.6.18-xen.hg.  The latter at some
time needed and may still need:

* xencons=xvc to stop the Xen console from mugging the serial console

* console=xvc to get a working console when PVFB is disabled.  By
  default, only console tty is enabled, which is a useless dummy
  without PVFB.

* console=xvc console=tty when PVFB is enabled, to enable both console
  tty (PVFB) and the Xen console xvc.

> The domU starts booting and stops after printing some texts to the tty
> console (I think it waits for the back-end to come-up)
> Then I execute the command <qemu-dm -M xenpv -d domid>. Then a black screen
> flashes for a fraction of a second and goes away.
> Nothing happens. So am I doing the write things. Or am I supposed to do some
> thing different?

Xend should start the backend automatically for you.  If it doesn't,
check its log for hints on what went wrong.  Also check qemu logs.

> (Do I need to start a VNC viewer in dom0 in case I am using the VNC option)

Yes.  The VNC option makes more sense in most circumstances.  For
instance, closing the viewer window doesn't kill your guest dead.

If you use a distro that provides virt-manager (a GUI to control your
virtual machines): virt-manager comes with an integrated viewer.

> in Xen 3.1 there was a tool vncfb . But that is missing in 3.2. I assume all
> of that functionality has been put into qemu-dm.


> In the thread
> http://lists.xensource.com/archives/html/xen-devel/2007-08/msg00351.html  it
> is mentioned about merging xenfb and xenconsoled into qemu-dm. So what is
> the purpose of xenconsoled . If I look through my system I find binaries
> like (/usr/bin/xencons , /usr/sbin/xenconsoled
> /usr/lib64/xen/bin/xenconsole). Could you please give me an idea what are
> these used for?

xenconsoled receives logs from hypervisor and guests and writes them
to log files, commonly in /var/lib/xen/

> Finally a logistics question:
> Like you have said in your reply 2.6.18 kernel is not usable for many
> purposes. But Xen website does not provide support for any later version of
> kernel for dom0. Are the Xen guys planning  to  provide  port for a later
> kernel like 2.6.23 /24?

The pvops effort is about getting Xen kernel bits integrated into
upstream Linux, so that we never again have to port them to later
kernel versions.

> So I am wondering if I use the Xen that comes inbuilt with Linux
> distributions like Fedora8 do I get all the pvops features that you are
> mentioning? But I guess Fedora8 has Xen 3.1.  And the current hypervisor is
> 3.2 . So all this make the whole thing a bit confusing.
> Thanks,
> Dushmanta

The Fedora 8 Xen kernel is a port to 2.6.21, but that's pretty much as
outdated and useless as .18.  Fedora 9 and later will provide Xen
through pvops in a *current* kernel.

Hypervisor version and domU kernel version are not closely coupled.
I would expect a pvops kernel guest to run fine both under a 3.1 and
3.2 hypervisor.

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