Why does the mbuf library support packet mbufs with smaller data room size than RTE_PKTMBUF_HEADROOM (e.g. [1]), when the Ethdev drivers (e.g. [2]) don't support it?
This goes all the way back to the first public release [3]. It seems crazy exotic, and should be removed for simplicity and a potential performance benefit. What am I missing here? Instead, the rte_pktmbuf_pool_create() functions should check that data_room_size >= RTE_PKTMBUF_HEADROOM. [1]: https://elixir.bootlin.com/dpdk/v25.07/source/lib/mbuf/rte_mbuf.h#L941 static inline void rte_pktmbuf_reset_headroom(struct rte_mbuf *m) { m->data_off = (uint16_t)RTE_MIN((uint16_t)RTE_PKTMBUF_HEADROOM, (uint16_t)m->buf_len); } [2]: https://elixir.bootlin.com/dpdk/v25.07/source/drivers/net/intel/i40e/i40e_rxtx.c#L609 mb->data_off = RTE_PKTMBUF_HEADROOM; [3]: https://git.dpdk.org/dpdk/commit/lib/librte_mbuf?id=af75078fece3615088e561357c1e97603e43a5fe +static inline void rte_pktmbuf_reset(struct rte_mbuf *m) +{ + uint32_t buf_ofs; + + m->pkt.next = NULL; + m->pkt.pkt_len = 0; + m->pkt.l2_len = 0; + m->pkt.l3_len = 0; + m->pkt.vlan_tci = 0; + m->pkt.nb_segs = 1; + m->pkt.in_port = 0xff; + + m->ol_flags = 0; + buf_ofs = (RTE_PKTMBUF_HEADROOM <= m->buf_len) ? + RTE_PKTMBUF_HEADROOM : m->buf_len; + m->pkt.data = (char*) m->buf_addr + buf_ofs; + + m->pkt.data_len = 0; + __rte_mbuf_sanity_check(m, RTE_MBUF_PKT, 1); +} Med venlig hilsen / Kind regards, -Morten Brørup
