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Date: Mon, 26 Aug 2013 16:21:31 +0200
From: Andre Oppermann <andre@freebsd.org>
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To: Gleb Smirnoff <glebius@FreeBSD.org>
Subject: Re: svn commit: r254805 - head/sys/sys
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On 26.08.2013 13:00, Gleb Smirnoff wrote:
> On Sat, Aug 24, 2013 at 07:58:36PM +0000, Andre Oppermann wrote:
> A> Author: andre
> A> Date: Sat Aug 24 19:58:36 2013
> A> New Revision: 254805
> A> URL: http://svnweb.freebsd.org/changeset/base/254805
> A>
> A> Log:
> A>   Add mtodo(m, o) macro taking an additional offset into the mbuf data section.
> A>
> A>   Sponsored by:	The FreeBSD Foundation
> A>
> A> Modified:
> A>   head/sys/sys/mbuf.h
> A>
> A> Modified: head/sys/sys/mbuf.h
> A> ==============================================================================
> A> --- head/sys/sys/mbuf.h	Sat Aug 24 19:51:18 2013	(r254804)
> A> +++ head/sys/sys/mbuf.h	Sat Aug 24 19:58:36 2013	(r254805)
> A> @@ -67,8 +67,10 @@
> A>   * type:
> A>   *
> A>   * mtod(m, t)	-- Convert mbuf pointer to data pointer of correct type.
> A> + * mtodo(m, o) -- Same as above but with offset 'o' into data.
> A>   */
> A>  #define	mtod(m, t)	((t)((m)->m_data))
> A> +#define	mtodo(m, o)	((void *)(((m)->m_data) + (o)))
>
> IMO, having a typecast would be better. Then mtodo() would be really same as
> mtod(), as stated in comment.

There was a big discussion about 10 month back when I did this change in my
tcp_workqueue branch with the typecast in.  The conclusion was that a typecast
is really not necessary and only causes one to type a lot more for the compiler
to throw away anyway.  But yes, the comment isn't perfect in that sense.

-- 
Andre