serial console & sysrq?

serial console & sysrq?

[Gerd Knorr]

  Hi,

is there some way to trigger sysrq from the serial console in
xenlinux?  With native linux it works by sending a break + sysrq
letter, in xenlinux it doesn't work that way though ...

cheers,

  Gerd

-- 
panic("it works"); /* avoid being flooded with debug messages */

RE: serial console & sysrq?

[Ian Pratt]

> is there some way to trigger sysrq from the serial console in 
> xenlinux?  With native linux it works by sending a break + 
> sysrq letter, in xenlinux it doesn't work that way though ...

I'm not entirely sure how 'break' is signalled from the UART. We'll
certainly fail to pass it on through xen to Linux as there's no side
channel.

One option would be to use a second serial line and to let Linux drive
it directly.

What I usually do is to switch to the Xen console and then send a debug
interrupt 'q', after having arranged for the debug intterupt handler to
call the sysrq function I'm interested in. All a bit gross.

Ian

Re: serial console & sysrq?

[Hollis Blanchard]

On Thursday 11 August 2005 05:16, Ian Pratt wrote:
> > is there some way to trigger sysrq from the serial console in
> > xenlinux?  With native linux it works by sending a break +
> > sysrq letter, in xenlinux it doesn't work that way though ...
>
> I'm not entirely sure how 'break' is signalled from the UART. We'll
> certainly fail to pass it on through xen to Linux as there's no side
> channel.

The hvc_console driver (used by kernels running on the pSeries hypervisor) has 
a similar problem. ^O is used as the break character there.

-- 
Hollis Blanchard
IBM Linux Technology Center

RE: serial console & sysrq?

[Ian Pratt]

 
> On Thursday 11 August 2005 05:16, Ian Pratt wrote:
> > > is there some way to trigger sysrq from the serial console in 
> > > xenlinux?  With native linux it works by sending a break + sysrq 
> > > letter, in xenlinux it doesn't work that way though ...
> >
> > I'm not entirely sure how 'break' is signalled from the UART. We'll 
> > certainly fail to pass it on through xen to Linux as 
> there's no side 
> > channel.
> 
> The hvc_console driver (used by kernels running on the 
> pSeries hypervisor) has a similar problem. ^O is used as the 
> break character there.

Seems reasonable. It would be good if someone could knock up a patch
that adds ^O sysrq support for xen console...

Ian