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Date: Thu, 27 Jun 2013 15:12:20 +0530
From: Aruna Balakrishnaiah <aruna@linux.vnet.ibm.com>
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To: "Luck, Tony" <tony.luck@intel.com>
CC: Kees Cook <keescook@chromium.org>,
        "jkenisto@linux.vnet.ibm.com" <jkenisto@linux.vnet.ibm.com>,
        Colin Cross <ccross@android.com>, LKML <linux-kernel@vger.kernel.org>,
        Anton Vorontsov <cbouatmailru@gmail.com>,
        "linuxppc-dev@ozlabs.org" <linuxppc-dev@ozlabs.org>,
        "paulus@samba.org" <paulus@samba.org>,
        Anton Blanchard <anton@samba.org>,
        "mahesh@linux.vnet.ibm.com" <mahesh@linux.vnet.ibm.com>
Subject: Re: [PATCH 3/3] powerpc/pseries: Support compression of oops text
 via pstore
References: <20130624061936.12963.72529.stgit@aruna-ThinkPad-T420> <20130624062316.12963.87911.stgit@aruna-ThinkPad-T420> <CAGXu5jJezRynWEBmmH8wp=pt1yEjukhe6Pg_aRcZP7E6t-1R=g@mail.gmail.com> <51C94101.3030702@linux.vnet.ibm.com> <3908561D78D1C84285E8C5FCA982C28F31C5376F@ORSMSX106.amr.corp.intel.com>
In-Reply-To: <3908561D78D1C84285E8C5FCA982C28F31C5376F@ORSMSX106.amr.corp.intel.com>
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Hi Tony,

On Tuesday 25 June 2013 09:32 PM, Luck, Tony wrote:
>> Introducing headersize in pstore_write() API would need changes at
>> multiple places whereits being called. The idea is to move the
>> compression support to pstore infrastructure so that other platforms
>> could also make use of it.
> Any thoughts on the back/forward compatibility as we switch to compressed
> pstore data?   E.g. imagine I have a system installed with some Linux distribution
> with a kernel too old to know about compressed pstore. I use that machine to
> run the latest kernels that do compression ... and one fine day one of them crashes
> hard - logging in compressed form to pstore. Now I boot my distro kernel to pick
> up the pieces ... what do I see in /sys/fs/pstore/*? Some compressed files? Can I
> read them with some tool?
>
> This somewhat of a corner case - but not completely unrealistic ... I'd at least
> like to be reassured that the old kernel won't choke when it sees the compressed
> blobs.

openssl command line tool can be used to decompress the compressed data of
the pstore file in the above scenario.

Usage:

cat <file> | openssl zlib -d

> -Tony
>

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