Hi,
I've noticed in lib/netdev-dpdk.c that __rte_pktmbuf_init() stores the
packet metadata right after "struct rte_mbuf", and before the buffer data:
/* start of buffer is just after mbuf structure */
m->buf_addr = (char *)m + sizeof(struct dp_packet);
(struct dp_packet has the rte_mbuf as first member if DPDK enabled)
However, lib/librte_mbuf/rte_mbuf.h seems to codify that the buffer
should start right after the rte_mbuf:
/**
* Given the buf_addr returns the pointer to corresponding mbuf.
*/
#define RTE_MBUF_FROM_BADDR(ba) (((struct rte_mbuf *)(ba)) - 1)
/**
* Given the pointer to mbuf returns an address where it's buf_addr
* should point to.
*/
#define RTE_MBUF_TO_BADDR(mb) (((struct rte_mbuf *)(mb)) + 1)
These macros are used for attaching/detaching mbuf's to each other. This
is the way the code retrieves the direct buffer from an indirect one,
and vica versa. I think if we want to keep the metadata feature (which I
guess is quite important), we need to add a pointer to rte_mbuf, which
helps the direct and indirect structs to find each other. Something like:
struct rte_mbuf *attach; /**< Points to the other buffer if this one
is (in)direct. Otherwise NULL. */
What do you think?
Regards,
Zoltan Kiss
