Re: [dpdk-dev] [PATCH 2/2] mbuf: reset nb_segs of chained packet

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 16 Nov 2017 18:05:35 +0400
Ilya Matveychikov <matvejchikov@gmail.com> wrote:

> Fixes: 139debc42dc0 ("mbuf: move chaining from ip_frag library")
> Cc: simon.kagstrom@netinsight.net
> 
> Signed-off-by: Ilya V. Matveychikov <matvejchikov@gmail.com>
> ---
>  lib/librte_mbuf/rte_mbuf.h | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index ce8a05ddf..2126dc94b 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -1828,9 +1828,12 @@ static inline int rte_pktmbuf_chain(struct rte_mbuf *head, struct rte_mbuf *tail
>  	head->nb_segs += tail->nb_segs;
>  	head->pkt_len += tail->pkt_len;
> 
> -	/* pkt_len is only set in the head */
> +	/* nb_segs and pkt_len are only set in the head */
> +	tail->nb_segs = 1;
>  	tail->pkt_len = tail->data_len;
> 
> +	__rte_mbuf_sanity_check(head, 1);
> +
>  	return 0;
>  }

My understanding is that nb_segs and pkt_len are only valid
in head. For other packets in the chain nb_segs and pkt_len
can be anything.