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


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


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

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

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);

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

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

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


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_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.


These functions were introduced in FreeBSD 8.0.
September 27, 2012 FreeBSD