Re: [dpdk-dev] [dpdk-stable] [PATCH v3 3/5] net/tap: fix check for mbuf's nb_segs failure

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 4/7/2020 4:38 PM, Stephen Hemminger wrote:
> On Tue, 7 Apr 2020 16:15:16 +0100
> Ferruh Yigit <ferruh.yigit@intel.com> wrote:
> 
>>> +static void
>>> +tap_rxq_pool_free(struct rte_mbuf *pool)
>>> +{
>>> +	struct rte_mbuf *mbuf = pool;
>>> +	uint16_t nb_segs = 1;
>>> +
>>> +	if (mbuf == NULL)
>>> +		return;
>>> +
>>> +	while (mbuf->next) {
>>> +		mbuf = mbuf->next;
>>> +		nb_segs++;
>>> +	}
>>> +	pool->nb_segs = nb_segs;
>>> +	rte_pktmbuf_free(pool);
>>> +}  
> 
> Since mbuf is going to be free, why bother with nb_segs.
> Since rte_pktmbuf_free takes NULL as an argument, and frees the m->next chain
> I don't see why not just
> 	rte_pktmbuf_free(pool)
> 

Chain is not constructed properly, 'nb_segs' is wrong, only 'rte_pktmbuf_free()'
call won't free all the chain but first mbuf.

This implementation is fixing 'nb_segs' sot that 'rte_pktmbuf_free()' can work
as you suggested.

Or I suggest iterate the list and fix all mbufs, instead of fixing 'nb_segs',
this may be one iteration less.