linux-kernel - Re: [RFC] [-mm] Remove 'unsafe' LZO decompressor

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Date:	Thu, 24 May 2007 11:50:55 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Michael-Luke Jones <mlj28@....ac.uk>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Richard Purdie <richard@...nedhand.com>
Subject: Re: [RFC] [-mm] Remove 'unsafe' LZO decompressor

On Thu, 24 May 2007 18:15:17 +0100
Michael-Luke Jones <mlj28@....ac.uk> wrote:

> Attached is a patch which may be desirable for -mm. It applies  
> directly to 2.6.22-rc2-mm1.
> 
> The patch removes the 'unsafe' LZO decompression function, lowering  
> the size of the minilzo.c file by nearly 500 out of an original 1727  
> lines. It also removes references to the 'unsafe' decompression  
> function in the public LZO header and the EXPORT_SYMBOL_GPL declaration.
> 
> This is intended to provoke some discussion over whether a  
> decompression function able to scribble on arbitrary memory is  
> desirable in the mainline kernel, whatever the performance increases.
> 
> Over and above the security/stability implications of using this  
> code, it can also be argued to represent an unnecessary duplication  
> of the vast majority of LZO decompression code. This is due to the  
> lack of likely in-kernel uses of the 'unsafe' function.
> 
> Only a single user for this 'unsafe' code has been suggested, the  
> 'Compressed Caching' project. This code is highly unlikely to move  
> into mainline in the same timeframe as the LZO code. All of the other  
> suggested uses require decompression of untrusted data, such that the  
> 'safe' function should be used.
> 
> Comments / disagreement all welcome :)

This is obviously a highly desirable thing to do for a number of reasons. 
But have we quantified the performance difference?
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