From: ebiederm@xmission.com (Eric W. Biederman)
To: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
Cc: vgoyal@redhat.com, cpw@sgi.com, kumagai-atsushi@mxc.nes.nec.co.jp,
        lisa.mitchell@hp.com, heiko.carstens@de.ibm.com,
        akpm@linux-foundation.org, kexec@lists.infradead.org,
        linux-kernel@vger.kernel.org, zhangyanfei@cn.fujitsu.com
References: <87txo5bxk4.fsf@xmission.com>
	<20130321.122501.82758179.d.hatayama@jp.fujitsu.com>
	<8738vp75cy.fsf@xmission.com>
	<20130321.151428.393714972.d.hatayama@jp.fujitsu.com>
Date: Wed, 20 Mar 2013 23:29:05 -0700
In-Reply-To: <20130321.151428.393714972.d.hatayama@jp.fujitsu.com> (HATAYAMA
	Daisuke's message of "Thu, 21 Mar 2013 15:14:28 +0900 (JST)")
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Subject: Re: [PATCH v3 18/21] vmcore: check if vmcore objects satify mmap()'s page-size boundary requirement
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HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com> 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.

Eric
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