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xen-users
Re: [Xen-users] Does XEN support crash carts?
> Clearly, I'm a newbie. Thanks for the tip
> on crash cart support (via 'xm console').
> It really helped - but I'm left with a nagging
> (newbie) KVM question. I'd also love to confirm
> my newfound serial-port understanding.
>
> I now see how to configure support for
> the physical serial port (i.e. see section 2.5.2 at
> http://tx.downloads.xensource.com/downloads/docs/user/).
Cool.
> It seems easy enough to 'switch' between
> domains/guests using the escape character
> mentioned. Once the serial connection is set/switched
> to be talking to domain0, I can see using a
> 'xm consoles' - or 'xm lists' - command to
> discover/choose active domain IDs. So everything
> looks
> fine via the crash cart's null modem cable (to/from
> the physical serial port). Right?
Right.
> Much goodness ;-) Is there anything missing?
> Maybe a listing of archived/saved VM images?
I'm not entirely clear what you mean here...
If you're using Xend's lifecycle management you can list all domains it knows
about (that is, including ones that are currently not running / suspended).
If you're not (i.e. just using config files) then you can only get
information on the currently running domains. ISTR the lifecycle management
stuff is still a "preview" not officially finished but I could be wrong here.
Does this answer your question?
> I just cannot seem to get my head around what
> is happening on the physical VGA/USB ports.
> What happens to these when one issues an 'xm console'
> command (in/to Domain0)?
>
> I wonder. As the serial--dev/console/--dev/ttyS0
> of each domain gets 'switched', is the
> monitor--virtual-framebuffer association *also*
> getting switched onto/off-of the physical VGA port?
> Are the virtual keyboards/mice of each domain
> *switched* - right along with the serial-port/console
> and the virtual framebuffer? If so ... well then ...
> more goodness ;-)
>
xm console doesn't actually switch ownership of the console port, it's just a
program that connects to a guest's virtual serial port and blats out data to
a terminal. It works just the same if you're using dom0's serial port, or
dom0's VGA console, or logged into dom0 over ssh.
dom0 retains ownership of the serial port, VGA, USB and almost all the other
hardware at all times (unless you explicitly give control of some PCI device
to a guest).
When you are talking directly to the IO devices on the host system, you're
talking to dom0. If you want to get to a guest's framebuffer / keyboard, you
can access it via dom0 - for instance by having domain 0 export it over the
network using VNC.
> I really appreciate the clarification. I
> apologize for being such a newbie :-( I've heard
> some claims about there being some sort of
> XEN limitation/deficiency here (and I've got
> some limitations on what I can presently just try
> myself). At any rate, the premise that XEN v3.x
> lacks any 'crash cart' support sounds like a myth.
> Maybe this is just an out-of-date notion.
Think of dom0 as being a combination of these things:
* IP KVM for the running domUs (can relay their framebuffer and mouse /
keyboard over the network)
* serial console concentrator for the domUs (can relay their serial console
over ssh / whatever - just log in to dom0 and run xm console)
* management module for all the domUs (can shut them down (politely, or not),
reboot them, etc without requiring login to the domU itself). It can also
core dump crashing domUs for later analysis, I believe.
dom0 is effectively like a software implementation of a sophisticated
management card, or like the hypervisor console found on IBM mainframes. It
just happens to also be a Linux environment. You just need to be able to
access dom0 over the network to do all these things; otherwise, log into dom0
with your crash cart and you can do this stuff using that instead.
Does that help clarify things a bit? The ability to do this sort of stuff is
one of the big wins of virtual machine technology on servers - (Xen's
competitors tend to offer this type of functionality too).
Don't hesistate to ask if you have any more questions.
Cheers,
Mark
PS. another "management processor"-like feature is a software watchdog device
which runs *outside* of the virtual machine so that no amount of corruption
of the domU kernel can cause it to fail. I'm working on this at the moment,
and hoping to get it in to the 3.0.6 release at latest.
> Thanks for all the help.
>
> --- Jayson Vantuyl <jvantuyl@xxxxxxxxxxxxxx> wrote:
> > This is what I do.
> >
> > On Mar 7, 2007, at 1:26 PM, Foreman, Tim wrote:
> > > I'm kind of a newbie to Xen, but can't you just
> >
> > log into
> >
> > > the Dom0 host - the physical box running Xen -
> >
> > through the serial
> >
> > > port, or the crash cart KVM, and then connect to
> >
> > the DomU guest
> >
> > > consoles using 'xm console DOMAIN'?
> > >
> > > --
> > > Timothy W. Foreman ~ Security Administrator ~
> >
> > tforeman@xxxxxxxxx
> >
> > > (651) 365-4181 ~ Internet Broadcasting ~
> >
> > www.ibsys.com
> >
> > > --
> > > The Onion: Have you decided what you want to be
> >
> > when you grow up?
> >
> > > Berkeley Breathed: Dad. The rest is frosting.
> >
> > --
> > Jayson Vantuyl
> > Systems Architect
> > Engine Yard
> > jvantuyl@xxxxxxxxxxxxxx
>
> ___________________________________________________________________________
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--
Dave: Just a question. What use is a unicyle with no seat? And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!
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