NAME

     drbr, drbr_free, drbr_enqueue, drbr_dequeue, drbr_dequeue_cond, drbr_flush, drbr_empty, drbr_inuse, —
     network driver interface to buf_ring

SYNOPSIS

     #include <sys/param.h>
     #include <net/if.h>
     #include <net/if_var.h>

     void
     drbr_free(struct buf_ring *br, struct malloc_type *type);

     int
     drbr_enqueue(struct ifnet *ifp, struct buf_ring *br, struct mbuf *m);

     struct mbuf *
     drbr_dequeue(struct ifnet *ifp, struct buf_ring *br);

     struct mbuf *
     drbr_dequeue_cond(struct ifnet *ifp, struct buf_ring *br, int (*func) (struct mbuf *, void *), void *arg);

     void
     drbr_flush(struct ifnet *ifp, struct buf_ring *br);

     int
     drbr_empty(struct ifnet *ifp, struct buf_ring *br);

     int
     drbr_inuse(struct ifnet *ifp, struct buf_ring *br);

DESCRIPTION

     The drbr functions provide an API to network drivers for using buf_ring(9) for enqueueing and dequeueing
     packets.  This is meant as a replacement for the IFQ interface for packet queuing.  It allows a packet to
     be enqueued with a single atomic and packet dequeue to be done without any per-packet atomics as it is
     protected by the driver's tx queue lock.  If INVARIANTS is enabled, drbr_dequeue() will assert that the tx
     queue lock is held when it is called.

     The drbr_free() function frees all the enqueued mbufs and then frees the buf_ring.

     The drbr_enqueue() function is used to enqueue an mbuf to a buf_ring, falling back to the ifnet's IFQ if
     ALTQ(4) is enabled.

     The drbr_dequeue() function is used to dequeue an mbuf from a buf_ring or, if ALTQ(4) is enabled, from the
     ifnet's IFQ.

     The drbr_dequeue_cond() function is used to conditionally dequeue an mbuf from a buf_ring based on whether
     func returns TRUE or FALSE.

     The drbr_flush() function frees all mbufs enqueued in the buf_ring and the ifnet's IFQ.

     The drbr_empty() function returns TRUE if there are no mbufs enqueued, FALSE otherwise.

     The drbr_inuse() function returns the number of mbufs enqueued.  Note to users that this is intrinsically
     racy as there is no guarantee that there will not be more mbufs when drbr_dequeue() is actually called.
     Provided the tx queue lock is held there will not be less.

RETURN VALUES

     The drbr_enqueue() function returns ENOBUFS if there are no slots available in the buf_ring and 0 on
     success.

     The drbr_dequeue() and drbr_dequeue_cond() functions return an mbuf on success and NULL if the buf_ring is
     empty.

HISTORY

     These functions were introduced in FreeBSD 8.0.