linux-kernel - RE: [PATCH 3/3] powerpc/pseries: Support compression of oops text via pstore

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Date:	Tue, 25 Jun 2013 16:02:58 +0000
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Aruna Balakrishnaiah <aruna@...ux.vnet.ibm.com>,
	Kees Cook <keescook@...omium.org>
CC:	"jkenisto@...ux.vnet.ibm.com" <jkenisto@...ux.vnet.ibm.com>,
	Colin Cross <ccross@...roid.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Anton Vorontsov <cbouatmailru@...il.com>,
	"linuxppc-dev@...abs.org" <linuxppc-dev@...abs.org>,
	"paulus@...ba.org" <paulus@...ba.org>,
	"Anton Blanchard" <anton@...ba.org>,
	"mahesh@...ux.vnet.ibm.com" <mahesh@...ux.vnet.ibm.com>
Subject: RE: [PATCH 3/3] powerpc/pseries: Support compression of oops text
 via pstore

> 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.

-Tony

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