1.\" Copyright (c) 2010 by The DragonFly Project and Samuel J. Greear. 2.\" All rights reserved. 3.\" 4.\" This code is derived from software contributed to The DragonFly Project 5.\" by Samuel J. Greear <sjg@thesjg.com> 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in 15.\" the documentation and/or other materials provided with the 16.\" distribution. 17.\" 3. Neither the name of The DragonFly Project nor the names of its 18.\" contributors may be used to endorse or promote products derived 19.\" from this software without specific, prior written permission. 20.\" 21.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 22.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 23.\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 24.\" FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 25.\" COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 26.\" INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING, 27.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 28.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 29.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 30.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 31.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.Dd March 17, 2010 35.Os 36.Dt lwbuf 9 37.Sh NAME 38.Nm lwbuf_alloc , 39.Nm lwbuf_free , 40.Nm lwbuf_page , 41.Nm lwbuf_kva , 42.Nm lwbuf_set_global 43.Nd lightweight buffers 44.Sh SYNOPSIS 45.In cpu/lwbuf.h 46.Ft "struct lwbuf *" 47.Fn lwbuf_alloc "vm_page_t m" 48.Ft void 49.Fn lwbuf_free "struct lwbuf *lwb" 50.Ft vm_page_t 51.Fn lwbuf_page "struct lwbuf *lwb" 52.Ft vm_offset_t 53.Fn lwbuf_kva "struct lwbuf *lwb" 54.Ft void 55.Fn lwbuf_set_global "struct lwbuf *lwb" 56.Sh DESCRIPTION 57The 58.Nm lwbuf 59kernel functions are used for maintaining a lightweight reference to and 60accessing an arbitrary 61.Vt vm_page_t . 62.Pp 63.Fn lwbuf_alloc 64returns a pointer to a lightweight buffer representing 65.Fa m . 66.Pp 67.Fn lwbuf_free 68frees all resources associated with the lightweight buffer 69.Fa lwb . 70.Pp 71.Fn lwbuf_page 72and 73.Fn lwbuf_kva 74return the associated 75.Vt vm_page_t 76or 77.Vt vm_offset_t 78of the lightweight buffer 79.Fa lwb . 80.Pp 81.Fn lwbuf_set_global 82ensures that a 83.Vt vm_offset_t 84previously obtained through 85.Fa lwbuf_kva 86will be valid on all processors without subsequent calls to 87.Fa lwbuf_kva . 88It should not be used. 89.Sh IMPLEMENTATION NOTES 90The implementation of 91.Nm lwbuf 92is CPU-dependent. 93On i386, pages taken from 94per-processor pools of kernel virtual address space (KVA) are used to map 95arbitrary 96.Vt vm_page_t 97objects. 98On x86_64 such tricks are unnecessary, the 99kernel maintains a direct map of KVA covering all physical memory. 100.Pp 101Lightweight buffers are thread and cross-processor safe with a number of 102limitations. 103Allocated buffers are not internally cached or reference counted. 104Any consumer of lightweight buffers may elect to share allocated buffers 105or allow them to be used in other threads or on other processors, but care 106must be taken. 107Buffers must be externally refcounted or in some other manner 108freed only after last use. 109.Sh HISTORY 110A 111.Nm lwbuf 112implementation first appeared in 113.Dx 2.5 . 114.Sh AUTHORS 115The 116.Nm lwbuf 117implementation and this manpage were written by 118.An Samuel J. Greear . 119