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.Dt LWBUF 9 36.Os 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" "struct lwbuf *" 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 . 66The 67.Fa lwb 68argument is an lwbuf structure, used to avoid allocation of an lwbuf 69on the x86_64 architecture. 70.Pp 71.Fn lwbuf_free 72frees all resources associated with the lightweight buffer 73.Fa lwb . 74.Pp 75.Fn lwbuf_page 76and 77.Fn lwbuf_kva 78return the associated 79.Vt vm_page_t 80or 81.Vt vm_offset_t 82of the lightweight buffer 83.Fa lwb . 84.Pp 85.Fn lwbuf_set_global 86ensures that a 87.Vt vm_offset_t 88previously obtained through 89.Fa lwbuf_kva 90will be valid on all processors without subsequent calls to 91.Fa lwbuf_kva . 92It should not be used. 93.Sh IMPLEMENTATION NOTES 94The implementation of 95.Nm lwbuf 96is CPU-dependent. 97On x86_64 the 98kernel maintains a direct map of KVA covering all physical memory. 99.Pp 100Lightweight buffers are thread and cross-processor safe with a number of 101limitations. 102Allocated buffers are not internally cached or reference counted. 103Any consumer of lightweight buffers may elect to share allocated buffers 104or allow them to be used in other threads or on other processors, but care 105must be taken. 106Buffers must be externally refcounted or in some other manner 107freed only after last use. 108.Sh HISTORY 109A 110.Nm lwbuf 111implementation first appeared in 112.Dx 2.5 . 113.Sh AUTHORS 114The 115.Nm lwbuf 116implementation and this manpage were written by 117.An Samuel J. Greear . 118