Re: xm pause <domain>

[Daniel Stekloff <dsteklof@us.ibm.com>]

On Sun, 2005-01-23 at 15:34, Kip Macy wrote:
> > Cool!
> 
> Enthusiasm is always welcome  :-).
> 
> >
> > Some information here:
> > http://lkcd.sourceforge.net/doc/linuxworld2000/LKCD.html
> >
> > There may be some more hanging around somewhere - I suspect that's the paper I
> > remembered reading...
> >
> > Of course, for non-Linux guests these tools won't necessarily be much (any?)
> > use, so ELF format core files might prove more generally useful (I don't know
> > if the LKCD lcrash tool can support ELF dump files - it'd be real nice if it
> > did).
> 
> Having worked _briefly_ with elf coredumps as a starting point for
> process checkpointing, I don't think they would be well suited for this.
> An elf coredump defines all of a running applications mappings in the
> program header. In a VM, there will be MANY mappings, which may be
> fragmented, corresponding to many page directory pointers. If all I
> cared about were the kernel state, that would be fine, but I think users
> would like to be able to see what processes were doing at the time.
> Examining the user-state will of course be very OS-specific.
> Nonetheless, I think that it is important that the information be there,
> so that if someone does choose to develop the tool, the pieces will
> already be there.
> 
> Any corrections or contrary opinions are welcome ...


Hi!

Wouldn't ELF header based dump files, like those used for netdump or
diskdump, be useful because you could use gdb to read them? Isn't the
kexec/kdump project doing something in this area? Since kexec/kdump has
quite a bit of backing, wouldn't it be helpful to dump something in the
same format so a single tool like crash could read vmcores dumped by
either method? 

I haven't had the chance to look this up yet, but does a crashdump done
through Xen require the dumping OS to help with the dump? Or, does the
hypervisor do it alone? Obviously, if the hypervisor can do it alone, it
would be better to just have crashdumps with Xen rather than requiring
kexec and invoking another kernel. If, however, the dumping OS is
required to perform the dump through Xen, then kdump may be the best way
to go. 

I'm interested in this area and would like to offer my help testing,
developing, etc. I will definitely look into how the dump is done using
Xen to start. Please let me know if I can help.

Thanks,

Dan



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