linux-kernel - Re: [patch 1/2] kdump: Initialize vmcoreinfo note at startup

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Message-Id: <20110920155912.d107fd49.akpm@google.com>
Date:	Tue, 20 Sep 2011 15:59:12 -0700
From:	Andrew Morton <akpm@...gle.com>
To:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
Cc:	vgoyal@...hat.com, ebiederm@...ssion.com,
	mahesh@...ux.vnet.ibm.com, schwidefsky@...ibm.com,
	heiko.carstens@...ibm.com, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch 1/2] kdump: Initialize vmcoreinfo note at startup

On Tue, 20 Sep 2011 16:34:01 +0200
Michael Holzheu <holzheu@...ux.vnet.ibm.com> wrote:

> From: Michael Holzheu <holzheu@...ux.vnet.ibm.com>
> 
> Currently the vmcoreinfo note is only initialized in case of kdump. On s390
> it is possible to create kernel dumps with other dump mechanisms than kdump
> (e.g. via hypervisor dump or stand-alone dump tools). For those dumps it
> would also be desirable to include the vmcoreinfo data. To accomplish this,
> with this patch the vmcoreinfo ELF note is always initialized, not only in
> case of a (kdump) crash. On s390 we will add an ABI defined pointer at
> a well known address to vmcoreinfo so that dump analysis tools are able to
> find this information.
> 
> In particular on s390 we have a tool named zgetdump. With this tool it is
> possible to convert dump formats on the fly using fuse. E.g. you can mount a
> s390 stand-alone dump as ELF dump. When this is done, the tool finds the
> vmcoreinfo in the stand-alone dump via the well known ABI defined address and
> it creates the respective VMCOREINFO ELF note in the output ELF dump. This then
> can be used e.g. by makedumpfile for dump filtering.  No more need for a
> vmlinux file with debug information.
> 
> So this will look like the following:
> $ zgetdump --mount standalone.dump -f elf /mnt
> $ ls /mnt
>   dump.elf
> $ readelf -n /mnt/dump.elf
> $ ...
>   VMCOREINFO            0x00000474      Unknown note type: (0x00000000)
> $ makedumpfile -c -d 31 /mnt/dump.elf dump.kdump
> 
> ...
>
> -void crash_save_vmcoreinfo(void)
> +static void update_vmcoreinfo_note(void)
>  {
> -	u32 *buf;
> +	u32 *buf = (u32 *) vmcoreinfo_note;

The cast is unneeded?

>  	if (!vmcoreinfo_size)
>  		return;
> -
> -	vmcoreinfo_append_str("CRASHTIME=%ld", get_seconds());
> -
> -	buf = (u32 *)vmcoreinfo_note;

As was the space you added after it ;)

>  	buf = append_elf_note(buf, VMCOREINFO_NOTE_NAME, 0, vmcoreinfo_data,
>  			      vmcoreinfo_size);
> -
>  	final_note(buf);
>  }

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