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

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

>      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?

Just thought I'd clarify here:

it's no longer the case (as of 3.0.4) that domains have to export their own 
displays using VNC.  Dom0 can do it for them with no VNC configuration 
required in the guest.

If you can get graphics out of dom0 somehow (over ssh, over VNC, from the VGA 
port) you should be able to get the framebuffers and serial ports of the 
guest OSes.

Cheers,
Mark

>      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
>
> ___________________________________________________________________________
>
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> >
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> > >
> > > _______________________________________________
> > > Xen-users mailing list
>
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>
>
>
>
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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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