linux-kernel - Re: [RFC][PATCH] PM / Hibernate: Modify signature used to mark swap

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Date:	Sun, 03 Oct 2010 07:44:53 +1100
From:	Nigel Cunningham <nigel@...onice.net>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] PM / Hibernate: Modify signature used to mark swap

Hi.

On 30/09/10 08:02, Rafael J. Wysocki wrote:
> On Wednesday, September 29, 2010, Nigel Cunningham wrote:
>> Hi.
>>
>> On 30/09/10 07:13, Rafael J. Wysocki wrote:
>>> From: Rafael J. Wysocki<rjw@...k.pl>
>>> Subject: PM / Hibernate: Modify signature used to mark swap
>>>
>>> Since we are adding compression to the kernel's hibernate code,
>>> change signature used by it to mark swap spaces, so that earlier
>>> kernels don't attempt to restore compressed images they cannot
>>> handle.
>>>
>>> Signed-off-by: Rafael J. Wysocki<rjw@...k.pl>
>>> ---
>>>    kernel/power/swap.c |    6 +++---
>>>    1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> Index: linux-2.6/kernel/power/swap.c
>>> ===================================================================
>>> --- linux-2.6.orig/kernel/power/swap.c
>>> +++ linux-2.6/kernel/power/swap.c
>>> @@ -29,7 +29,7 @@
>>>
>>>    #include "power.h"
>>>
>>> -#define SWSUSP_SIG	"S1SUSPEND"
>>> +#define HIBERNATE_SIG	"LINHIB0001"
>>>
>>>    /*
>>>     *	The swap map is a data structure used for keeping track of each page
>>> @@ -195,7 +195,7 @@ static int mark_swapfiles(struct swap_ma
>>>    	if (!memcmp("SWAP-SPACE",swsusp_header->sig, 10) ||
>>>    	    !memcmp("SWAPSPACE2",swsusp_header->sig, 10)) {
>>>    		memcpy(swsusp_header->orig_sig,swsusp_header->sig, 10);
>>
>> if no compression
>>
>>> -		memcpy(swsusp_header->sig,SWSUSP_SIG, 10);
>>
>> else
>>
>>> +		memcpy(swsusp_header->sig, HIBERNATE_SIG, 10);
>>
>> ??
>
> I thought about that, but we'll need to drop the old signature when the image
> format changes (I think it will after your patch series) anyway.  And the
> benefit is not really worth it IMO (it only affects people using the in-kernel
> hibernation on x86-64).

Okay. I'm just a little weary because if everything I want to get in 
gets in, we're going to then be changing this signature multiple times. 
I want to eventually reach a situation where we have a 'proper' header 
section to the image that stores (among other things) whether 
compression is enabled and which cryptoapi algorithm is used, allowing a 
person to en/disable compression at runtime without recompiling or 
rebooting. I suppose if I seek to put that stuff in earlier rather than 
later, that will simplify things.

Oh, while I'm writing to you: let's not worry about getting my patches 
in for 2.6.37. I won't be working on them much today, and want to put 
the time into making sure they're right before they get merged. As you 
said - let's seek to get things right first time.

Regards,

Nigel
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