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Re: [Xen-devel] pv_ops dom0 and kernel console output problem

On Wed, Dec 31, 2008 at 09:44:52AM +1100, Jeremy Fitzhardinge wrote:
> Pasi Kärkkäinen wrote:
> >Reading pv_ops wiki page I noticed this:
> >
> >"If the domain crashes very early, before any output appears on the 
> >console,
> >then booting with: "earlyprintk=xen" should provide some useful 
> >information.
> >If you are running a debug build of Xen hypervisor (set "debug = y" in
> >Config.mk in the Xen source tree), then you should get crash dumps on the
> >Xen console. You can view those with "xm dmesg"."
> >
> >So I guess earlyprintk=xen is only useful if you're running debug build of
> >Xen hypervisor.. ?
> earlyprintk=xen has the effect of directing the kernel's console output 
> via the console output hypercall.  domU kernel's are not generally 
> allowed to do this, but it is when you compile Xen in debug mode.  dom0, 
> however, uses the Xen console in the normal case, so it doesn't need a 
> debug Xen build.  But when Xen switches its console output to serial the 
> kernel's output goes with it, so if you want it to appear on VGA you 
> need to use the VGA console output (make sure your kernel has all the VT 
> console options enabled).

Thanks for clearing that up!

-- Pasi

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