DRBR(9)

NAME
drbr, drbr_free, drbr_enqueue, drbr_dequeue, drbr_dequeue_cond, drbr_flush, drbr_empty, drbr_inuse, drbr_stats_update, - 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);
void
drbr_stats_update(struct ifnet *ifp, int len, int mflags);

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.

The drbr_stats_update() function updates the number of bytes and the number of multicast packets sent.

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.