linux-kernel - Re: [RFC-PATCH] lib: add byteorder helpers for the aligned case

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Date:	Fri, 16 May 2008 20:35:56 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Harvey Harrison <harvey.harrison@...il.com>
cc:	Bryan Wu <cooloney@...nel.org>, Jie Zhang <jie.zhang@...log.com>,
	Oliver Neukum <oliver@...kum.org>, <david-b@...bell.net>,
	<greg@...ah.com>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC-PATCH] lib: add byteorder helpers for the aligned case

On Fri, 16 May 2008, Harvey Harrison wrote:

> Some users know the pointer they are writing to are aligned,
> rather than doing *(__le16 *)ptr = cpu_to_le16(val) add helpers
> wrapping this up that have the same convention as put_unaligned_le/be.
> 
> Signed-off-by: Harvey Harrison <harvey.harrison@...il.com>
> ---
> Alan, as requested, I'm looking around a bit to see if there are actual
> users for this.  But it does make a nice complement to the unaligned
> versions.

This is great -- thanks!  I've wanted this sort of thing for a long
time.  There's a good chance that the SCSI core could make use of
it.  Try looking at the prep functions in sd.c and sr.c.

> +static inline void put_le16(u16 val, void *ptr)
> +{
> +	*(__le16 *)ptr = cpu_to_le16(val);
> +}

Is this able to do the byte rearrangement at compile time if val is a 
compile-time constant?  I imagine it would.

Alan Stern

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