[Crash-utility] Re: [PATCH 1/2] Add x86_64 linux-2.6.27 support: Catch up the PAGE_OFFSET change.

[Dave Anderson]

Ken'ichi Ohmichi wrote:
> Hi Dave,
>
> [ snip ]
> 
> I think that a new virtualization_init() function is a good idea.
> 
> How about checking whether "Xen" exists in PT_NOTE section of an vmcore
> at virtualization_init()? I feel that it is safer than reading a xen_start_info
> pointer.
> 
> $ readelf -n vmcore
> Notes at offset 0x00000120 with length 0x00001388:
>   Owner         Data size       Description
>   CORE          0x00000150      NT_PRSTATUS (prstatus structure)
>   Xen           0x00000020      Unknown note type: (0x01000002)  <----- HERE
>   CORE          0x00000150      NT_PRSTATUS (prstatus structure)
>   Xen           0x00000020      Unknown note type: (0x01000002)  <----- HERE
>   Xen           0x00000050      Unknown note type: (0x01000001)  <----- HERE
>   VMCOREINFO_XEN                0x00000fe4      Unknown note type: (0x00000000)
> $

Well there may be a couple issues with that approach.  First, we need
a way to handle/recognize it on live systems.  And second, I believe we'll need
a way to differentiate a pv_ops/xen kernel from a "dedicated" xen kernel.
And my guess is that the vmcore notes will not differentiate between the
two "flavors" of xen kernel (unless there's an entry in the VMCOREINFO_XEN
that will somehow differentiate the two).

I'm thinking now that a pv_ops/xen kernel should not be simply handled by
making the current XEN() macro usable.  Looking at the various usages of XEN(),
I think that many of them may *only* be applicable to dedicated xen kernels.
So I believe there should be a new PV_XEN() macro, and ultimately PV_KVM()
and PV_VMI() macros.  Given that all of the pv_ops kernels are the "same"
vmlinux, it's possible that in some ways things may be simplified.  But I
strongly doubt that the use of the current XEN() macro will work.

So I think it's best to take it one step at a time.  The first step will be
to get crash working with 2.6.27 bare-metal kernels, and disallow the setting
of the ARCH_XEN flag used by the XEN() macro.  Until I actually see a "real"
pv_ops/xen kernel dumpfile, it's not even worth pre-coding for it.

Dave