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DRBR(9)			 BSD Kernel Developer's	Manual		       DRBR(9)

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 avail-
     able 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.

BSD			      September	27, 2012			   BSD

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | HISTORY

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