Re: [PATCH v3 18/21] vmcore: check if vmcore objects satifymmap()'s page-size boundary requirement

From: HATAYAMA Daisuke
Date: Thu Mar 21 2013 - 02:47:13 EST

From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Subject: Re: [PATCH v3 18/21] vmcore: check if vmcore objects satify mmap()'s page-size boundary requirement
Date: Wed, 20 Mar 2013 23:29:05 -0700

> HATAYAMA Daisuke <d.hatayama@xxxxxxxxxxxxxx> writes:
>> Do you mean for each range represented by each PT_LOAD entry, say:
>> [p_paddr, p_paddr + p_memsz]
>> extend it as:
>> [rounddown(p_paddr, PAGE_SIZE), roundup(p_paddr + p_memsz, PAGE_SIZE)].
>> not only objects in vmcore_list, but also updating p_paddr and p_memsz
>> members themselves of each PT_LOAD entry? In other words, there's no
>> new holes not referenced by any PT_LOAD entry since the regions
>> referenced by some PT_LOAD entry, themselves are extended.
> No. p_paddr and p_memsz as exported should remain the same.
> I am suggesting that we change p_offset.
> I am suggesting to include the data in the file as if we had changed
> p_paddr and p_memsz.
>> Then, the vmcores seen from read and mmap methods are coincide in the
>> direction of including both ranges
>> [rounddown(p_paddr, PAGE_SIZE), p_paddr]
>> and
>> [p_paddr + p_memsz, roundup(p_paddr + p_memsz, PAGE_SIZE)]
>> are included in both vmcores seen from read and mmap methods, although
>> they are originally not dump target memory, which you are not
>> problematic for ease of implementation.
>> Is there difference here from you understanding?
> Preserving the actual PT_LOAD segments p_paddr and p_memsz values is
> important. p_offset we can change as much as we want. Which means there
> can be logical holes in the file between PT_LOAD segments, where we put
> the extra data needed to keep everything page aligned.

So, I have to make the same question again. Is it OK if two vmcores
are different? How do you intend the ``extra data'' to be deal with? I
mean mmap() has to export part of old memory as the ``extra data''.

If you think OK, I'll fill the ``extra data'' with 0 in case of read
method. If not OK, I'll fill with the corresponding part of old


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