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 4:45 PM, Ferruh Yigit wrote:
> 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.

No, my bad. It will free all and will work as expected. But this is to fix the
mbuf sanity checks when they are enabled.

> 
> 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.
>