[Crash-utility] handling missing kdump pages in diskdump format

[Vivek Goyal]

On Tue, Mar 20, 2007 at 11:18:02AM +0900, Ken'ichi Ohmichi wrote:
> 
> Hi Bob,
> 
> Thank you for the great report.
> 
> 2007/03/14 08:40:16 +0530, Vivek Goyal <vgoyal at in.ibm.com> wrote:
> >> =====================================
> >> Can ELF Dumpfiles Solve This Problem?
> >> =====================================
> >> 
> >> To achieve correctness with ELF dumpfiles, one could perhaps remap the
> >> four types of pages to the three types of ELF representations so that
> >> "A) Not In The Address Space" and "B) Excluded Type" were both mapped
> >> to "1) Not In The Address Space".  Then "C) Zero Content" would map
> >> to "2) Not In The File, Zero Fill".  You would lose the ability to
> >> know if a page were missing because it was never in the address space
> >> in the first place, or because it was excluded because of its type.
> >> But if you read a zero, you'd know it really was a zero.
> >> 
> >
> >I think this is the way to go. Why would I like to know if a page was
> >never present or mkdumpfile filtered it out? I think we can live with that
> >and lets just not create any sort of mapping for excluded pages in finally
> >generated ELF headers.
> 
> In the above way, I worry that the crash utility cannot get the
> relocatable information (machdep->machspec->phys_start) on ia64.
> At ia64_calc_phys_start(), the crash utility gets phdr->p_paddr
> of region 5 memory section as the relocatable information.
> If the start of region 5 is excluded, the crash gets different
> phdr->p_paddr in the above way.
> 

Sorry, I don't understand it. vmcore ELF headers should give enough
information to determine what's the kernel's virtual and physical
address.  Why should I have to have access to a particular page and because
of that take the wrong route and try to map filtered pages. 

Is ia64 kernel mapped in region 5? If yes, I won't filter out kernel
pages?

If not, still I don't understand how does it help mapping non-kernel pages
and returning zeros for that?

Thanks
Vivek