Awesome answers! The XEN community rocks!
It now seems as if there is shred of truth
to the 'myth'. Still, XEN already has almost
everything anyone might want - so I'm thinking of
ways I might contribute to fix what I'm thinking
might be a *very* smallish XEN limitation. Please
bear with me. I'll attempt to explain.
Recall from the beginning of this
thread that I mentioned that VNC is almost
always good enough. I was bringing up the
very rare 'crash cart' case. For instance,
a NIC card might be down/dysfunctional.
Even with a down NIC, the null modem (cross-over)
cable to the physical serial port works
(as explained - Dom0 mediates/relays the chosen
DomU serial traffic, etc.). However ... unless
I misunderstand something about VNC, VNC is
*NOT* going to work with a down NIC. If I
recall correctly, VNC requires a TCP/IP
connection. Of course, I'm newbie ignorant
of any special features tha might have been
added to XvncD. Am I spouting nonsense here?
So, in the glorious ignorance of a newbie,
I'm guessing that the physical VGA/USB ports
are not 'active' (on the back of the box).
Any attempt to cable up a crash cart LCD/monitor,
keyboard and/or mouse, to these inactive
physical ports, will not work. Right? Or
did I miss something major?
I'd really appreciate knowing if I'm
just all muddled here. If I'm right, then
I suspect that this is the genesis of the
nit that I've heard picked with XEN.
If this is a *tiny* XEN nit, then I'm very
tempted to see what might be done to fix it.
Since this is such a once-in-a-blue-moon nit,
I'm thinking perhaps nobody else has bothered
with it. Obviously, this isn't a huge
priority (because VNC is *almost* always good
enough). All the same, this sounds like a
potentially fun project (albeit a project
whose scope might be surprising - depending on
many things that I presently know very, very
little about ;-).
Thanks again,
--- Mark Williamson <mark.williamson@xxxxxxxxxxxx>
wrote:
> > 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
> >
> >
>
___________________________________________________________________________
> >_________ Looking for earth-friendly autos?
> > Browse Top Cars by "Green Rating" at Yahoo! Autos'
> Green Center.
> > http://autos.yahoo.com/green_center/
> >
> > _______________________________________________
> > Xen-users mailing list
>
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