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Date: Fri, 10 Sep 2004 14:13:38 +0100 (BST)
From: "Brian Somers" <brian@Awfulhak.org>
To: "Dima Dorfman" <dd@freebsd.org>
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cc: Brian Somers <brian@Awfulhak.org>
cc: freebsd-net@freebsd.org
Subject: Re: uma_zcreate() call from kern_mbuf.c - bug?
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> Brian Somers <brian@Awfulhak.org> wrote:
>> Of course m_get() et. al. seem to manage to get MSIZE aligned pointers
>> back
>> from uma_zalloc_arg(zone_mbuf...) anyway, but surely that's an
>> implementation
>> side effect and the align argument should be corrected.
>
> This change looks right to me, but I'm hardly an expert here.
>
>> There should probably also be a KASSERT here to ensure that MSIZE is
>> sane
>
> This might be better as a CTASSERT:
>
> Index: kern_mbuf.c
> ===================================================================
> RCS file: /ref/cvsf/src/sys/kern/kern_mbuf.c,v
> retrieving revision 1.3
> diff -u -r1.3 kern_mbuf.c
> --- kern_mbuf.c	2 Aug 2004 00:18:35 -0000	1.3
> +++ kern_mbuf.c	10 Sep 2004 06:53:10 -0000
> @@ -123,6 +123,9 @@
>  static void	mb_reclaim(void *);
>  static void	mbuf_init(void *);
>
> +/* Ensure that MSIZE doesn't break dtom(). */
> +CTASSERT((((MSIZE - 1) ^ MSIZE) + 1) >> 1 == MSIZE);
> +
>  /*
>   * Initialize FreeBSD Network buffer allocation.
>   */
> @@ -135,7 +138,7 @@
>  	 * Configure UMA zones for Mbufs, Clusters, and Packets.
>  	 */
>  	zone_mbuf = uma_zcreate("Mbuf", MSIZE, mb_ctor_mbuf, mb_dtor_mbuf,
> -	    NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_MAXBUCKET);
> +	    NULL, NULL, MSIZE - 1, UMA_ZONE_MAXBUCKET);
>  	zone_clust = uma_zcreate("MbufClust", MCLBYTES, mb_ctor_clust,
>  	    mb_dtor_clust, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_REFCNT);
>  	if (nmbclusters > 0)
>
>

Agreed.  I didn't know about CTASSERT()!

Cheers.

--
Brian <brian@Awfulhak.org>                        <brian@[uk.]FreeBSD.org>
      <http://www.Awfulhak.org>                   <brian@[uk.]OpenBSD.org>
Don't _EVER_ lose your sense of humour !