linux-ext4 - Re: [PATCH 2/3] lib: improve the performance of memcpy and memmove of the general version

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Message-Id: <B1BAFDD8-BA1F-4C03-A19E-09DF91CD98FF@dilger.ca>
Date:	Fri, 3 Sep 2010 12:16:57 -0600
From:	Andreas Dilger <adilger.kernel@...ger.ca>
To:	Florian Weimer <fweimer@....de>
Cc:	miaox@...fujitsu.com, Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Mason <chris.mason@...cle.com>,
	Theodore Ts'o <tytso@....edu>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Btrfs <linux-btrfs@...r.kernel.org>,
	Linux Ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 2/3] lib: improve the performance of memcpy and memmove of the general version

On 2010-09-03, at 05:03, Florian Weimer wrote:

> * Miao Xie:
> 
>> EXPORT_SYMBOL(memcpy);
> 
> I think you need to change that to EXPORT_SYMBOL_GPL, because the code
> is now licensed under the GPL, and not the GPL plus kernel exceptions
> (whatever they are, but they undoubtly exist), unlike the original
> implementation.

Ouch.  That would basically make it impossible to implement a non-GPL module.  Also, this should only apply to the "lib" version of the memcpy() routine, not the arch-specific ones that are written in assembly (maybe that already is true, I'm not sure).

Lustre is GPL, so it isn't fatal for us, but it definitely seems draconian, and almost a reason not to include this patch into the kernel.  Also, given that the original code is LGPL (which allows linking to non-GPL code) this seems counter to the intent of the original authors.

I suspect there isn't anything so brilliant in the glibc memcpy() that it couldn't be re-implemented without copying the code.  "implement memcpy with aligned machine-word-sized chunks" would be enough for anyone to reimplement it without ever having come close to the glibc code.

Cheers, Andreas

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