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

[Michael Holzheu <holzheu@linux.vnet.ibm.com>]

Hello Vivek,

On Tue, 7 May 2013 12:37:01 -0400
Vivek Goyal <vgoyal@redhat.com> wrote:

> 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

Fine, we will do that.
 
> 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.

Ok, we will try that. There might be a problem that our ELF notes
content is also in the new kernel memory. But also for that there be a
solution.

Michael