Copyright (c) 2009 Bitgravity Inc
Written by: Kip Macy <kmacy@@FreeBSD.org>
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$FreeBSD$

.Dd January 30, 2012 .Dt DRBR 9 .Os .Sh NAME .Nm drbr , .Nm drbr_free , .Nm drbr_enqueue , .Nm drbr_dequeue , .Nm drbr_dequeue_cond , .Nm drbr_flush , .Nm drbr_empty , .Nm drbr_inuse , .Nm drbr_stats_update , .Nd network driver interface to buf_ring .Sh SYNOPSIS n sys/param.h n net/if.h n net/if_var.h .Ft void .Fn drbr_free "struct buf_ring *br" "struct malloc_type *type" .Ft int .Fn drbr_enqueue "struct ifnet *ifp" "struct buf_ring *br" "struct mbuf *m" .Ft struct mbuf * .Fn drbr_dequeue "struct ifnet *ifp" "struct buf_ring *br" .Ft struct mbuf * .Fn drbr_dequeue_cond "struct ifnet *ifp" "struct buf_ring *br" "int (*func) (struct mbuf *, void *)" "void *arg" .Ft void .Fn drbr_flush "struct ifnet *ifp" "struct buf_ring *br" .Ft int .Fn drbr_empty "struct ifnet *ifp" "struct buf_ring *br" .Ft int .Fn drbr_inuse "struct ifnet *ifp" "struct buf_ring *br" .Ft void .Fn drbr_stats_update "struct ifnet *ifp" "int len" "int mflags" .Sh DESCRIPTION The .Nm functions provide an API to network drivers for using .Xr 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 .Dv INVARIANTS is enabled, .Fn drbr_dequeue will assert that the tx queue lock is held when it is called.

p The .Fn drbr_free function frees all the enqueued mbufs and then frees the buf_ring.

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

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

p The .Fn drbr_dequeue_cond function is used to conditionally dequeue an mbuf from a buf_ring based on whether .Fa func returns .Dv TRUE or .Dv FALSE .

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

p The .Fn drbr_empty function returns .Dv TRUE if there are no mbufs enqueued, .Dv FALSE otherwise.

p The .Fn 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 .Fn drbr_dequeue is actually called. Provided the tx queue lock is held there will not be less.

p The .Fn drbr_stats_update function updates the number of bytes and the number of multicast packets sent. .Sh RETURN VALUES The .Fn drbr_enqueue function returns .Er ENOBUFS if there are no slots available in the buf_ring and .Dv 0 on success.

p The .Fn drbr_dequeue and .Fn drbr_dequeue_cond functions return an mbuf on success and .Dv NULL if the buf_ring is empty. .Sh HISTORY These functions were introduced in .Fx 8.0 .