Re: [dpdk-dev] [PATCH v2 1/5] mbuf: fix clone support when application uses private mbuf data

[Zoltan Kiss <zoltan.kiss@linaro.org>]

On 26/03/15 15:59, Olivier Matz wrote:
> Add a new private_size field in mbuf structure that should
> be initialized at mbuf pool creation. This field contains the
> size of the application private data in mbufs.
>
> Introduce new static inline functions rte_mbuf_from_indirect()
> and rte_mbuf_to_baddr() to replace the existing macros, which
> take the private size in account when attaching and detaching
> mbufs.
>
> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> ---
>   app/test-pmd/testpmd.c     |  1 +
>   examples/vhost/main.c      |  2 +-
>   lib/librte_mbuf/rte_mbuf.c |  1 +
>   lib/librte_mbuf/rte_mbuf.h | 44 ++++++++++++++++++++++++++++++++++----------
>   4 files changed, 37 insertions(+), 11 deletions(-)
>
> diff --git a/app/test-pmd/testpmd.c b/app/test-pmd/testpmd.c
> index 3057791..c5a195a 100644
> --- a/app/test-pmd/testpmd.c
> +++ b/app/test-pmd/testpmd.c
> @@ -425,6 +425,7 @@ testpmd_mbuf_ctor(struct rte_mempool *mp,
>   	mb->tx_offload   = 0;
>   	mb->vlan_tci     = 0;
>   	mb->hash.rss     = 0;
> +	mb->priv_size    = 0;
>   }
>
>   static void
> diff --git a/examples/vhost/main.c b/examples/vhost/main.c
> index c3fcb80..d542461 100644
> --- a/examples/vhost/main.c
> +++ b/examples/vhost/main.c
> @@ -139,7 +139,7 @@
>   /* Number of descriptors per cacheline. */
>   #define DESC_PER_CACHELINE (RTE_CACHE_LINE_SIZE / sizeof(struct vring_desc))
>
> -#define MBUF_EXT_MEM(mb)   (RTE_MBUF_FROM_BADDR((mb)->buf_addr) != (mb))
> +#define MBUF_EXT_MEM(mb)   (rte_mbuf_from_indirect(mb) != (mb))
>
>   /* mask of enabled ports */
>   static uint32_t enabled_port_mask = 0;
You would need to fix pktmbuf_detach_zcp as well, but see my reply to 
Konstantin.

> diff --git a/lib/librte_mbuf/rte_mbuf.c b/lib/librte_mbuf/rte_mbuf.c
> index 526b18d..e095999 100644
> --- a/lib/librte_mbuf/rte_mbuf.c
> +++ b/lib/librte_mbuf/rte_mbuf.c
> @@ -125,6 +125,7 @@ rte_pktmbuf_init(struct rte_mempool *mp,
>   	m->pool = mp;
>   	m->nb_segs = 1;
>   	m->port = 0xff;
> +	m->priv_size = 0;
>   }
>
>   /* do some sanity checks on a mbuf: panic if it fails */
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index 17ba791..45ac948 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -317,18 +317,42 @@ struct rte_mbuf {
>   			/* uint64_t unused:8; */
>   		};
>   	};
> +
> +	uint16_t priv_size;       /**< size of the application private data */
>   } __rte_cache_aligned;
>
>   /**
> - * Given the buf_addr returns the pointer to corresponding mbuf.
> + * Return the mbuf owning the data buffer address of an indirect mbuf.
> + *
> + * @param mi
> + *   The pointer to the indirect mbuf.
> + * @return
> + *   The address of the direct mbuf corresponding to buffer_addr.
>    */
> -#define RTE_MBUF_FROM_BADDR(ba)     (((struct rte_mbuf *)(ba)) - 1)
> +static inline struct rte_mbuf *
> +rte_mbuf_from_indirect(struct rte_mbuf *mi)
> +{
> +       struct rte_mbuf *md;
> +       md = (struct rte_mbuf *)((char *)mi->buf_addr - sizeof(*mi) -
> +	       mi->priv_size);
> +       return md;
> +}
>
>   /**
> - * Given the pointer to mbuf returns an address where it's  buf_addr
> - * should point to.
> + * Return the buffer address embedded in the given mbuf.
> + *
> + * @param md
> + *   The pointer to the mbuf.
> + * @return
> + *   The address of the data buffer owned by the mbuf.
>    */
> -#define RTE_MBUF_TO_BADDR(mb)       (((struct rte_mbuf *)(mb)) + 1)
> +static inline char *
> +rte_mbuf_to_baddr(struct rte_mbuf *md)
> +{
> +       char *buffer_addr;
> +       buffer_addr = (char *)md + sizeof(*md) + md->priv_size;
> +       return buffer_addr;
> +}
>
>   /**
>    * Returns TRUE if given mbuf is indirect, or FALSE otherwise.
> @@ -744,12 +768,12 @@ static inline void rte_pktmbuf_attach(struct rte_mbuf *mi, struct rte_mbuf *md)
>   static inline void rte_pktmbuf_detach(struct rte_mbuf *m)
>   {
>   	const struct rte_mempool *mp = m->pool;
> -	void *buf = RTE_MBUF_TO_BADDR(m);
> -	uint32_t buf_len = mp->elt_size - sizeof(*m);
> -	m->buf_physaddr = rte_mempool_virt2phy(mp, m) + sizeof (*m);
> +	void *buf = rte_mbuf_to_baddr(m);
> +	unsigned mhdr_size = (char *)buf - (char *)m;
Minor nit: I think "sizeof(*m) + m->priv_size" would be much more clear, 
like you did above. In fact, this might worth its own inline function, 
and then you can substitute mhdr_size below.

>
> +	m->buf_physaddr = rte_mempool_virt2phy(mp, m) + mhdr_size;
>   	m->buf_addr = buf;
> -	m->buf_len = (uint16_t)buf_len;
> +	m->buf_len = (uint16_t)(mp->elt_size - mhdr_size);
>
>   	m->data_off = (RTE_PKTMBUF_HEADROOM <= m->buf_len) ?
>   			RTE_PKTMBUF_HEADROOM : m->buf_len;
> @@ -774,7 +798,7 @@ __rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
>   		 *  - free attached mbuf segment
>   		 */
>   		if (RTE_MBUF_INDIRECT(m)) {
> -			struct rte_mbuf *md = RTE_MBUF_FROM_BADDR(m->buf_addr);
> +			struct rte_mbuf *md = rte_mbuf_from_indirect(m);
>   			rte_pktmbuf_detach(m);
>   			if (rte_mbuf_refcnt_update(md, -1) == 0)
>   				__rte_mbuf_raw_free(md);
>