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

[Steffen Hulegaard <shulegaa@xxxxxxxxx>]

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



 
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