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Re: [Xen-devel] Re: [PATCH]: kexec: framework and i386

On Fri, Apr 21, 2006 at 03:10:33PM +0900, Akio Takebe wrote:
> Hi, Horms and Mark
> This is good work!
> It is very necessary for debugging hypervisor or domain0.
> I'm not clear at some points.
> 1. Is this feature available on uni-processor machine?

At this stage only uni-processor is supported. However, the framework
supports SMP, and Magnus and I are planning to fill in those bits soon.
Actually, this is the next thing on my list of things to do.

> 2. Could you explain more detail usage?

The usage is mostly the same as kexec in the Linux kernel.  You can
kexec from xen into another kernel by using kexec -l, kexec -e, as per

kexec -l /boot/vmlinux --append "ro root=/dev/hda..."
kexec -e

And you can load a kernel that will be run on system crash using
kexec -p. This is discussed at some length in Documentation/kdump/kdump.txt
of the linux source tree. Those instructions can be followed
verbatim for xen.

The main difference with kdump, is that instead of using the crashdump
command line option to linux, you use the kdump_megabytes and
kdump_megabytes_base command line options to xen. When running xen the
crashdump linux command line option is ignored.

The reason for moving the option from linux to xen is that it seems that
the memory needs to be reserved by xen before it starts dom0. The reason
that there are two options instead of one is for simplicity.  Linux
provides infastructure to read the more complex compound option, xen
does not. This can be changed if it is a problem.

In summary, for kdump "linux crashdump=64M@16M"
becomes "xen kdump_megabytes=64 kdump_megabytes_base=16"

The other main point to note for users is that while the following
transition is possible: xen -> linux.  But xen -> xen and linux -> xen
is currently not possible.  This is because kexec-tool, the user-space
component of kexec does not understand enough about xen, and thus needs
to be enhanced in order to make this possible.

> Mark, what do you think about this kdump implementation?
> Best Regards,
> Akio Takebe


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