linux-kernel - Re: [RFC][PATCH 0/2]efi_pstore: Avoid missing panic message in NVRAM

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Date:	Thu, 5 Jul 2012 09:20:36 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Seiji Aguchi <seiji.aguchi@....com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Luck, Tony (tony.luck@...el.com)" <tony.luck@...el.com>,
	"mikew@...gle.com" <mikew@...gle.com>,
	"Matthew Garrett (mjg@...hat.com)" <mjg@...hat.com>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: Re: [RFC][PATCH 0/2]efi_pstore: Avoid missing panic message in NVRAM

On Tue, Jul 03, 2012 at 11:33:57PM +0000, Seiji Aguchi wrote:
> [Problem]
> Current efi_pstore simply overwrites existing entries in NVRAM.
> So, if 2nd panic happens before a user checks 1st panic message, 1st panic message will be lost.

I thought the rule was entries do not get overwritten until they are
deleted first.  Perhaps that is just an APEI thing, but it seems like that
should be a good rule for EFI too.

Mainly because there is very little userspace apps that actually clear the
old error records.  So this could become a common problem.

Unless we are implementing a flight recorder option which explicitly
states overwrite older entries?

Cheers,
Don

> 
> [Solution]
> To avoid missing 1st panic message, this patch introduce a rule checking if existing entries in NRAM are erasable to efi_pstore.
>  
> [Patch Descriptions]
>  
>  [PATCH 1/2] Duplicate a shared code between write and erase callbacks  
>  
>   Currently, efi_pstore driver shares a code erasing existing entries in NVRAM with write and erase callbacks.
>   But there some cases we should avoid erasing existing entries in write callback. (Please see PATCH 2/2).
>   This patch duplicates the code so that write and erase callbacks work independently. 
>  
>  
>  [PATCH 2/2] write callback: Check if existing entry is erasable
>  
>   this patch introduce a rule checking if existing entries in NRAM are erasable to efi_pstore.
>   With this patch, if previous event is panic, efi_pstore never overwrite it.
> 
>  
>   drivers/firmware/efivars.c |   94 +++++++++++++++++++++++++++++++++++++++++++-
>   fs/pstore/platform.c       |    4 +-
>   include/linux/pstore.h     |    5 ++
>   3 files changed, 99 insertions(+), 4 deletions(-)
>  
>  Seiji
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