1.\" Copyright (c) 2009 Bitgravity Inc 2.\" Written by: Kip Macy <kmacy@FreeBSD.org> 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.Dd September 18, 2026 27.Dt BUF_RING 9 28.Os 29.Sh NAME 30.Nm buf_ring , 31.Nm buf_ring_alloc , 32.Nm buf_ring_free , 33.Nm buf_ring_enqueue , 34.Nm buf_ring_dequeue_mc , 35.Nm buf_ring_dequeue_sc , 36.Nm buf_ring_count , 37.Nm buf_ring_empty , 38.Nm buf_ring_full , 39.Nm buf_ring_peek , 40.Nm buf_ring_drops 41.Nd multi-producer, {single, multi}-consumer lock-less ring buffer 42.Sh SYNOPSIS 43.In sys/param.h 44.In sys/buf_ring.h 45.Ft struct buf_ring * 46.Fn buf_ring_alloc "int count" "struct malloc_type *type" "int flags" "lock" 47.Ft void 48.Fn buf_ring_free "struct buf_ring *br" "struct malloc_type *type" 49.Ft int 50.Fn buf_ring_enqueue "struct buf_ring *br" "void *buf" 51.Ft void * 52.Fn buf_ring_dequeue_mc "struct buf_ring *br" 53.Ft void * 54.Fn buf_ring_dequeue_sc "struct buf_ring *br" 55.Ft int 56.Fn buf_ring_count "struct buf_ring *br" 57.Ft int 58.Fn buf_ring_empty "struct buf_ring *br" 59.Ft int 60.Fn buf_ring_full "struct buf_ring *br" 61.Ft void * 62.Fn buf_ring_peek "struct buf_ring *br" 63.Ft uint64_t 64.Fn buf_ring_drops "struct buf_ring *br" 65.Sh DESCRIPTION 66The 67.Nm 68functions provide a lock-less multi-producer and lock-less multi-consumer as 69well as single-consumer ring buffer. 70.Pp 71The 72.Fn buf_ring_alloc 73function is used to allocate a buf_ring ring buffer with 74.Fa count 75slots using malloc_type 76.Fa type 77and memory flags 78.Fa flags . 79The single consumer interface is protected by 80.Fa lock . 81Supported lock types are 82.Xr mutex 9 , 83.Xr rwlock 9 , 84and 85.Xr rmlock 9 . 86.Pp 87The 88.Fn buf_ring_free 89function is used to free a buf_ring. 90The user is responsible for freeing any enqueued items. 91.Pp 92The 93.Fn buf_ring_enqueue 94function is used to enqueue a buffer to a buf_ring. 95.Pp 96The 97.Fn buf_ring_dequeue_mc 98function is a multi-consumer safe way of dequeueing elements from a buf_ring. 99.Pp 100The 101.Fn buf_ring_dequeue_sc 102function is a single-consumer interface to dequeue elements - requiring 103the user to serialize accesses with a lock. 104.Pp 105The 106.Fn buf_ring_count 107function returns the number of elements in a buf_ring. 108.Pp 109The 110.Fn buf_ring_empty 111function returns 112.Dv TRUE 113if the buf_ring is empty, 114.Dv FALSE 115otherwise. 116.Pp 117The 118.Fn buf_ring_full 119function returns 120.Dv TRUE 121if no more items can be enqueued, 122.Dv FALSE 123otherwise. 124.Pp 125The 126.Fn buf_ring_peek 127function returns a pointer to the last element in the buf_ring if the 128buf_ring is not empty, 129.Dv NULL 130otherwise. 131.Pp 132The 133.Fn buf_ring_drops 134functions returns how many times the 135.Fn buf_ring_enqueue 136was not able to queue an element due to no available slots. 137.Sh RETURN VALUES 138The 139.Fn buf_ring_enqueue 140function return 141.Er ENOBUFS 142if there are no available slots in the buf_ring. 143.Sh HISTORY 144These functions were introduced in 145.Fx 8.0 . 146