Re: [dpdk-dev] [PATCH v4 1/2] mbuf: add function returning default buffer address

[David Marchand <david.marchand@redhat.com>]

On Thu, Jan 10, 2019 at 11:40 PM Yongseok Koh <yskoh@mellanox.com> wrote:

> This patch introduces two new functions - rte_mbuf_buf_addr() and
> rte_mbuf_data_addr_default().
>
> rte_mbuf_buf_addr() reutrns the default buffer address of given mbuf which
>

returns


> comes after mbuf structure and private data.
>
> rte_mbuf_data_addr_default() returns the default address of mbuf data
> taking the headroom into account.
>
> Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
> ---
>
> Please ignore v3, there were errors with some compilers.
>
> v4:
> * fix compilation error due to the experimental tag
> * add warning of experimental tag to the comments
>
> v3:
> * rename functions
>
> v2:
> * initial implementation
>
>  lib/librte_mbuf/rte_mbuf.h | 46
> ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
>
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index bc562dc8a9..5787616999 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -788,8 +788,54 @@ rte_mbuf_from_indirect(struct rte_mbuf *mi)
>  }
>
>  /**
> + * Return the default buffer address of the mbuf.
>

Nit: missed it... s/default //

+ *
> + * @warning
> + * @b EXPERIMENTAL: This API may change without prior notice.
> + * This will be used by rte_mbuf_to_baddr() which has redundant code once
> + * experimental tag is removed.
>

Good point.
I wonder if we have a "todolist" for release n+2 so that we don't forget
about such things to do.
Thomas ?

+ *
> + * @param mb
> + *   The pointer to the mbuf.
> + * @param mp
> + *   The pointer to the mempool of the mbuf.
> + * @return
> + *   The pointer of the mbuf buffer.
> + */
> +static inline char * __rte_experimental
> +rte_mbuf_buf_addr(struct rte_mbuf *mb, struct rte_mempool *mp)
> +{
> +       char *buffer_addr;
> +
> +       buffer_addr = (char *)mb + sizeof(*mb) + rte_pktmbuf_priv_size(mp);
> +       return buffer_addr;
> +}
>

Nit:
+       return (char *)mb + sizeof(*mb) + rte_pktmbuf_priv_size(mp);

+
> +/**
> + * Return the default address of the beginning of the mbuf data.
> + *
> + * @warning
> + * @b EXPERIMENTAL: This API may change without prior notice.
> + *
> + * @param mb
> + *   The pointer to the mbuf.
> + * @return
> + *   The pointer of the beginning of the mbuf data.
> + */
> +static inline char * __rte_experimental
> +rte_mbuf_data_addr_default(struct rte_mbuf *mb)
> +{
> +       return rte_mbuf_buf_addr(mb, mb->pool) + RTE_PKTMBUF_HEADROOM;
> +}
> +
> +/**
>   * Return the buffer address embedded in the given mbuf.
>   *
> + * @note: Accessing mempool pointer of a mbuf is expensive because the
> + * pointer is stored in the 2nd cache line of mbuf. If mempool is known,
> it
> + * is better not to reference the mempool pointer in mbuf but calling
> + * rte_mbuf_buf_addr() would be more efficient.
> + *
>   * @param md
>   *   The pointer to the mbuf.
>   * @return
> --
> 2.11.0
>
>
Thanks Yongseok.
Reviewed-by: David Marchand <david.marchand@redhat.com>


-- 
David Marchand