Re: [Xen-users] Does XEN support crash carts?

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

>      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.

OK, cool.

>      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?

No, you're not.  However, if you install a VNC viewer on dom0 then you could 
fire it up on dom0's local console and get access to the domU framebuffer 
that way.

>      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?

They'll work, you just can only get domain 0 talking to you.  So you'll have 
dom0's VGA and USB connections; fire up the VNC viewer in dom0 and you'll be 
set.

Dom 0 is a full Linux in its own right, with access to all the hardware: just 
fire up an X server and it'll come out on the VGA port.  It's normally the 
only domain privileged to do this, but you can use it to get to everything 
else.

There's also a local console client that doesn't use any kind of networking, 
but VNC is nice because it easily extends to the networked case.

Does that solve your problem?

Cheers,
Mark

>      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
>
> ___________________________________________________________________________
>
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> >
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> > >
> > > _______________________________________________
> > > Xen-users mailing list
>
> === message truncated ===
>
>
>
>
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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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