Re: [uml-devel] Is there an easy way to do a stack dump on UML?

[Rob Landley <rob@landley.net>]

On Saturday 03 December 2005 00:00, Jeff Dike wrote:
> On Fri, Dec 02, 2005 at 09:44:20PM -0600, Rob Landley wrote:
> > I've never used mconsole.  Never needed it before.
> >
> > Perhaps if I attach to a serial console instead of stdio I can send sysrq
> > that way...
>
> No.  Just think a little.  Banging on the SysRq key on your keyboard can't
> do anything but send SysRq to the host.

I know.  That's why I asked.  I thought there might be some other key 
combination that could do the same thing for a UML console.  (QEMU listens to 
the tty to do various escapes in non-graphics mode, for example.)

> SysRq for a virtual machine has to be an out-of-band thing wrt the host. 

Yeah, sending compressed data across the console becomes a bit dangerous 
otherwise.  But again, the difference between a pipe and a tty is that a tty 
has out-of-band information attached.

Possibly a couple of different shift keys plus the character in question?  
(Something X wouldn't intercept first, qemu uses ctrl-alt and it seems to 
work for them.)  According to man 4 console_ioctl, TIOCLINUX subcode 6 gives 
me something called "shift_state", so maybe I can beat some information out 
of the tty to tell when the user hit "ctrl-alt t" and turn that into sysrq-t?  
In theory it might work both when stdin is a tty and via an xterm...

To-do item.  The documentation on this sucks pretty badly...

> For UML, that's mconsole.

Except that serial consoles can also do sysrq.  (I vaguely remember they send 
a break signal or some such.  Dunno how to do that on an emulated one...)

>     Jeff

Rob
-- 
Steve Ballmer: Innovation!  Inigo Montoya: You keep using that word.
I do not think it means what you think it means.


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