Dumpfile filtering and PGC_xxx flags

Dumpfile filtering and PGC_xxx flags

[Petr Tesarik]

Hello folks,

I've been trying to add support for xen-4.0+ to makedumpfile (a utility that 
can filter out some content from a kernel dump file). In particular, I'm now 
struggling with implementing option "-X", which should filter out all domU 
pages, but keep hypervisor internal data and dom0 pages. Unused pages (free 
pages, broken pages, offlined pages, etc.) should also be filtered out, 
because they are usually not needed for dump analysis.

I'm relying on the contents of frame_table to do the job, but I'm lost in the 
hierarchy of PGC_xxx flags. My first naive idea was that I could keep pages 
that have:

1. PGC_allocated and
2. the right owner (dom_xen, dom_io, or dom0).

But that doesn't include Xen internal structures. In fact, the page_info 
structs for pages corresponding to Xen code and static data seem to be 
completely unitialized (all zero).

Thanks for any advice,
Petr Tesarik
SUSE Linux

Re: Dumpfile filtering and PGC_xxx flags

[Jan Beulich]

>>> On 24.08.12 at 14:50, Petr Tesarik <ptesarik@suse.cz> wrote:
> Hello folks,
> 
> I've been trying to add support for xen-4.0+ to makedumpfile (a utility that 
> can filter out some content from a kernel dump file). In particular, I'm now 
> 
> struggling with implementing option "-X", which should filter out all domU 
> pages, but keep hypervisor internal data and dom0 pages. Unused pages (free 
> pages, broken pages, offlined pages, etc.) should also be filtered out, 
> because they are usually not needed for dump analysis.
> 
> I'm relying on the contents of frame_table to do the job, but I'm lost in 
> the 
> hierarchy of PGC_xxx flags. My first naive idea was that I could keep pages 
> that have:
> 
> 1. PGC_allocated and
> 2. the right owner (dom_xen, dom_io, or dom0).

That looks reasonable.

> But that doesn't include Xen internal structures. In fact, the page_info 
> structs for pages corresponding to Xen code and static data seem to be 
> completely unitialized (all zero).

Yes, because the page allocator never gets to see those pages.
But for the (static) Xen image it ought to be possible to determine
which pages it consists of without relying on struct page_info,
based on virtual address (and its translation to physical).

Jan