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Date: Fri, 19 Jun 2015 17:58:59 +0200
From: Olivier MATZ <olivier.matz@6wind.com>
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To: Cyril Chemparathy <cchemparathy@ezchip.com>, dev@dpdk.org
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Subject: Re: [dpdk-dev] [PATCH 08/10] librte_mbuf: Add
	rte_pktmbuf_mtod_offset()
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On 04/29/2015 06:15 PM, Cyril Chemparathy wrote:
> There are a number of instances in the code where rte_pktmbuf_mtod() is used
> to get the mbuf data pointer, only to add an offset before casting the result
> to some other header type.  This patch adds a new rte_pktmbuf_mtod_offset()
> macro to eliminate these awful double cast situations.
> 
> Signed-off-by: Cyril Chemparathy <cchemparathy@ezchip.com>
> ---
>  lib/librte_mbuf/rte_mbuf.h | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index 5ddd8dd..e8f1bf4 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -54,6 +54,7 @@
>   */
>  
>  #include <stdint.h>
> +#include <rte_common.h>
>  #include <rte_mempool.h>
>  #include <rte_memory.h>
>  #include <rte_atomic.h>
> @@ -1071,6 +1072,23 @@ static inline struct rte_mbuf *rte_pktmbuf_lastseg(struct rte_mbuf *m)
>  }
>  
>  /**
> + * A macro that points to an offset into the data in the mbuf.
> + *
> + * The returned pointer is cast to type t. Before using this
> + * function, the user must ensure that m_headlen(m) is large enough to
> + * read its data.

Small comment here: m_headlen(m) should be replaced by "the length of
the first segment". Indeed, there is no m_headlen() function (I see that
it is coming from a copy/paste of the mtod() comment). Could you
also fix it by the way?




> + *
> + * @param m
> + *   The packet mbuf.
> + * @param o
> + *   The offset into the mbuf data.
> + * @param t
> + *   The type to cast the result into.
> + */
> +#define rte_pktmbuf_mtod_offset(m, t, o)	\
> +	((t)((char *)(m)->buf_addr + (m)->data_off + (o)))
> +
> +/**
>   * A macro that points to the start of the data in the mbuf.
>   *
>   * The returned pointer is cast to type t. Before using this
> @@ -1082,7 +1100,7 @@ static inline struct rte_mbuf *rte_pktmbuf_lastseg(struct rte_mbuf *m)
>   * @param t
>   *   The type to cast the result into.
>   */
> -#define rte_pktmbuf_mtod(m, t) ((t)((char *)(m)->buf_addr + (m)->data_off))
> +#define rte_pktmbuf_mtod(m, t) rte_pktmbuf_mtod_offset(m, t, 0)
>  
>  /**
>   * A macro that returns the length of the packet.
>