[Xen-users] DomU Console Flow of Control

[John Riedl <riedl@xxxxxxxxxx>]

Hello all.  I've been running a Hardy Dom0/DomU for about 2.5 years.
Recently I upgraded my test DomU to Karmic because I needed some
upgraded tools on my desktop, and wanted to be sure I had an upgrade
path that would work.  I ran into the /proc/<pid>/mountinfo problem,
and had to upgrade the Dom0 to a newer Debian kernel.  (If you haven't
been down this path: Karmic requires at least a 2.6.26 kernel because
of some /proc updates.)  Then I had to upgrade my Dom0 to jaunty to
get the Xen 3.3 so Xen could decompress the newer kernels from Karmic.
 (If you haven't been down this path, newer linux kernels are
sometimes compressed with lzma or bzip2, which Xen 3.2 doesn't
understand.)  All seems to be well now -- except that I *cannot* get
the console working with my karmic DomU.  Today I even used the
xen-tools to create a brand spanking new karmic DomU.  Everything
worked out of the box -- but no console.  (There is a practical part
of me that says "quit worrying about having a console: embrace your
inner ssh".  However, I know that eventually my ssh is going to break
before a key deadline ...)

I've tried a million variants of hdc0/xdc0/tty0, and I figure it's
time to actually understand how this thing is supposed to work.  So:
can someone please explain what needs to be true for a xen DomU
console to work?  Tons of people are struggling with this problem in
all different variants of Xen, but I haven't yet found a clear,
concise outline of the basics of how it should work.  The key
questions are below.  If some xen hero provides answers, I volunteer
to write them up for the wiki to restore xen to the world :).  Here
are the key questions:

1) What is the relationship between xenconsole= and console= in the
"extra = " config parameter?
2) Is there a relationship between the Dom0 console and a DomU
console?  Are there settings that are required on the Dom0 for the
DomU console to work?
3) Is the foo in console=foo magic, interpreted by Xen in some
mysterious way, or is it just a choice that connects to a normal tty
in the domU?
4) Does the DomU need to have a /dev/foo for console=foo to work?  If
so, what should the properties of /dev/foo be?  (I created a /dev/xvc0
on one of my karmic installs, and it got auto-removed on reboot.
What's that all about?!)
5) Does the DomU need to run getty on the /dev/foo?  Conversely, is it
important that the DomU not run getty?  Karmic has changed its way of
running getty, which has added to the confusion, but once you find
/etc/init it's pretty easy to follow.
6) Are there key modules that a DomU needs to have in its initrd to
have the console work?

Has anyone been down this path with karmic before?  I'd like to
understand the general situation better, but specific advice would be
very welcome.

Thank you!
John

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