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.

Debian                                         September 27, 2012                                        DRBR(9)