Re: [Xen-devel] bugs in xen

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> I'm wondering, since I can control the machine after failure with
> linuxbios, if there's something useful we can do to help with these
> failures. What kind of info would you like to be able to recover from a
> failed machine? Could we do something like only use the low half of
> memory, and on restart/reset "core dump" the low half to the high half for 
> a post-mortem? If not that, are there other ways we could help? 

Interesting idea.

It would certainly be nice to have Xen's console ring buffer
moved to safety, if not the whole of the bottom half of memory.

I guess a newly booted Xen could go looking for the previous
console buffer and write it to the new console. Doing a xen_dmesg
would then enable you to read the last messages of the previous
boot as well as those of the new one.

To be fully useful, it would make sense to have Xen's console
ring also store console message from dom 0, since most Xen
'spontaneous reboots' turn out to actually be dom 0 failures.

[Other than this NMI h/w parity error handling bug it's been a
very long time since we had a bug that managed to cause a reboot
without logging something to a serial console. Without a serial
console, Xen normally has no way of logging things to an output
device, hence the wish to save the ring buffer.]

BTW: I've heard rumours that Linux 2.6 is getting some scheme for
having the newly booted kernel write out a core dump of the
previous. For domains >0, we should just have xend write out a
core dump, but for a dom 0 crash it might be possible to modify
the Linux scheme to be useful in a Xen environment.

Ian


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