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

[Ilya Matveychikov <matvejchikov@gmail.com>]

> On Nov 16, 2017, at 9:01 PM, Stephen Hemminger <stephen@networkplumber.org> wrote:
> 
> 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.

So why not to keep them in consistency with multi-seg logic?
I mean that pkt_len/nb_segs for the head always have meaning but for
the rest of chain pkt_len is the same as data_len and nb_segs := 1