linux-kernel - Re: [RFC] typechecking for get_unaligned/put

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Message-ID: <Pine.LNX.4.64.0610170825581.3962@g5.osdl.org>
Date:	Tue, 17 Oct 2006 08:28:48 -0700 (PDT)
From:	Linus Torvalds <torvalds@...l.org>
To:	David Howells <dhowells@...hat.com>
cc:	Al Viro <viro@....linux.org.uk>, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [RFC] typechecking for get_unaligned/put_unaligned 

On Tue, 17 Oct 2006, David Howells wrote:

> Al Viro <viro@....linux.org.uk> wrote:
> 
> > 	* sizeof(*ptr) should be one of 1, 2, 4, 8
> 
> Should we give an error if someone tries passing a 1-byte-sized memory location
> to get/put_unaligned()?  I suspect it might be best to reduce to a trivial
> direct assignment in that case.

Note that in some cases, you have different architectures having different 
sizes, and it could potentially be the case that one architecture has a 
1-byte thing, and another has a 2-byte thing.

It's unlikely to be an issue for single-byte cases, but it definitely 
happens for other equivalent things (ie "get_user()" often has 2 vs 4-byte 
accesses, and obviously the 4- vs 8-byte thing through 32/64-bit values 
depending on the size of the machine).

So at least in _theory_ it's quite possible that a single-byte access can 
make sense, simply because the size might depend on a config option.

		Linus
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