linux-kernel - Re: [PATCH 0/4] kdump: Allow ELF header creation in new kernel

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Date:	Tue, 7 May 2013 12:37:01 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	Jan Willeke <willeke@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
Subject: Re: [PATCH 0/4] kdump: Allow ELF header creation in new kernel

On Mon, May 06, 2013 at 03:09:55PM +0200, Michael Holzheu wrote:
> Hello Vivek,
> 
> For s390 we want to use /proc/vmcore for our SCSI stand-alone
> dump (zfcpdump). We have support where the first HSA_SIZE bytes are
> saved into a hypervisor owned memory area (HSA) before the kdump
> kernel is booted. When the kdump kernel starts, it is restricted
> to use only HSA_SIZE bytes.
> 

Hi Michael,

Hatayama is changing /proc/vmcore interface to support mmap(). Can you
please rebase your changes on top of those patches.

http://thread.gmane.org/gmane.linux.kernel/1477622

Secondly, I think /proc/vmcore does not have to know whether elf
headers are in old memory or new memory. Given that s390 is taking
a deviation, so it now becomes an arch specific detail. Can't we
just create few arch specific helper functions to retrieve and free
elf headers.

- arch_get_crash_headers()
	- All arch except return elfcorehdr_add except s390.
- arch_read_crash_header_data()
	- All arch just call into read_from_oldmem() except s390. We
  	  can provide a generic implementation in /proc/vmcore.c so
	  all other arch can use that generic implementation.  Or
	  use symbol override trick.
- arch_free_crash_headers()
	- All arch do nothing except s390 which can reclaim the memory
 	  for elf headers prepared. Generic code has parsed/copied the
	  headers by now.

What do you think? Above 3 calls should solve the problem and allow
arch to handle elf headers differently. And generic implementation
still keeps common logic for processing headers.

Thanks
Vivek
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