Re: [dpdk-dev] [PATCH 1/2] mbuf: Add rte_pktmbuf_copy

[Olivier MATZ <olivier.matz@6wind.com>]

On 07/10/2015 01:37 AM, Stephen Hemminger wrote:
> From: Stephen Hemminger <shemming@brocade.com>
>
> Added rte_pktmbuf_copy() function since copying multi-part
> segments is common issue and can be problematic.
>
> Signed-off-by: Mike Davison <mdavison@brocade.com>
> Reviewed-by: Stephen Hemminger <shemming@brocade.com>
> ---
>   lib/librte_mbuf/rte_mbuf.h | 59 ++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 59 insertions(+)
>
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index 80419df..f0a543b 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -60,6 +60,7 @@
>   #include <rte_atomic.h>
>   #include <rte_prefetch.h>
>   #include <rte_branch_prediction.h>
> +#include <rte_memcpy.h>
>
>   #ifdef __cplusplus
>   extern "C" {
> @@ -1272,6 +1273,64 @@ static inline int rte_pktmbuf_is_contiguous(const struct rte_mbuf *m)
>   	return !!(m->nb_segs == 1);
>   }
>
> +/*
> + * Creates a copy of the given packet mbuf.
> + *
> + * Walks through all segments of the given packet mbuf, and for each of them:
> + *  - Creates a new packet mbuf from the given pool.
> + *  - Copy segment to newly created mbuf.
> + * Then updates pkt_len and nb_segs of the new packet mbuf to match values
> + * from the original packet mbuf.
> + *
> + * @param md
> + *   The packet mbuf to be copied.
> + * @param mp
> + *   The mempool from which the mbufs are allocated.
> + * @return
> + *   - The pointer to the new mbuf on success.
> + *   - NULL if allocation fails.
> + */
> +static inline struct rte_mbuf *rte_pktmbuf_copy(struct rte_mbuf *md,
> +		struct rte_mempool *mp)
> +{
> +	struct rte_mbuf *mc = NULL;
> +	struct rte_mbuf **prev = &mc;
> +
> +	do {
> +		struct rte_mbuf *mi;
> +
> +		mi = rte_pktmbuf_alloc(mp);
> +		if (unlikely(mi == NULL)) {
> +			rte_pktmbuf_free(mc);
> +			return NULL;
> +		}
> +

I think we should check that the destination mbuf is large enough
to store the segment data. Then we have 2 options on failure:
- split the original segment into several destination segments
- return an error


> +		mi->data_off = md->data_off;
> +		mi->data_len = md->data_len;
> +		mi->port = md->port;
> +		mi->vlan_tci = md->vlan_tci;
> +		mi->tx_offload = md->tx_offload;
> +		mi->hash = md->hash;
> +
> +		mi->next = NULL;
> +		mi->pkt_len = md->pkt_len;
> +		mi->nb_segs = md->nb_segs;
> +		mi->ol_flags = md->ol_flags;
> +		mi->packet_type = md->packet_type;
> +
> +		rte_memcpy(rte_pktmbuf_mtod(mi, char *),
> +			   rte_pktmbuf_mtod(md, char *),
> +			   md->data_len);
> +
> +		*prev = mi;
> +		prev = &mi->next;
> +	} while ((md = md->next) != NULL);
> +
> +	*prev = NULL;
> +	__rte_mbuf_sanity_check(mc, 1);
> +	return mc;
> +}
> +
>   /**
>    * Dump an mbuf structure to the console.
>    *
>