Re: [dpdk-users] A minor suggestion to the comment of the rte_eth_tx_burst() of dpdk-16.04

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2016-06-10 19:09, Wu, Xiaoban:
> Dear DPDK Users,
> 
> 
> I have a very small suggestion to the comment of the rte_eth_tx_burst(). It is not a big deal to the experienced users, but I think this will make the new users know how to use this function more clearly and see the big picture easily.
> 
> 
> The comment of "tx_pkts" says:
> 
>  * @param tx_pkts
>  *   The address of an array of *nb_pkts* pointers to *rte_mbuf* structures
>  *   which contain the output packets.
> 
> 
> I am a beginner of DPDK. If I see this comment I would probably naively use rte_zmalloc() to construct such pointer array, for each pointer I use rte_malloc() to allocate memory, and finally fill the memory starting from the position (pointed by the macro rte_pktmbuf_mtod()) with real packet content(header and payload).
> 
> 
> But I just find that the rte_eth_tx_burst() will call the rte_pktmbuf_free() to free the struct rte_mbuf. In default, "CONFIG_RTE_LIBRTE_MBUF_DEBUG=n", this means it will skip the __rte_mbuf_sanity_check(), and will finally get into rte_mempool_put(). Since above construction process skip the construction of the field "struct rte_mempool", it means the "struct rte_mempool" field is null in each packet "struct rte_mbuf"(of course, all the fields are zero). Hence it will finally cause segmentation fault.
> 
> 
> Thus, I have a very small suggestion, please add something like "It is recommended that the tx_pkts is constructed by rte_pktmbuf_pool_create() combined with rte_mempool_get_bulk(), if not please make sure the fields of the struct rte_mbuf are correctly configured."

Good suggestion.
Olivier do you agree?