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. The 70.Fa lwb 71argument is unused on the i386 architecture. 72.Pp 73.Fn lwbuf_free 74frees all resources associated with the lightweight buffer 75.Fa lwb . 76.Pp 77.Fn lwbuf_page 78and 79.Fn lwbuf_kva 80return the associated 81.Vt vm_page_t 82or 83.Vt vm_offset_t 84of the lightweight buffer 85.Fa lwb . 86.Pp 87.Fn lwbuf_set_global 88ensures that a 89.Vt vm_offset_t 90previously obtained through 91.Fa lwbuf_kva 92will be valid on all processors without subsequent calls to 93.Fa lwbuf_kva . 94It should not be used. 95.Sh IMPLEMENTATION NOTES 96The implementation of 97.Nm lwbuf 98is CPU-dependent. 99On i386, pages taken from 100per-processor pools of kernel virtual address space (KVA) are used to map 101arbitrary 102.Vt vm_page_t 103objects. 104On x86_64 such tricks are unnecessary, the 105kernel maintains a direct map of KVA covering all physical memory. 106.Pp 107Lightweight buffers are thread and cross-processor safe with a number of 108limitations. 109Allocated buffers are not internally cached or reference counted. 110Any consumer of lightweight buffers may elect to share allocated buffers 111or allow them to be used in other threads or on other processors, but care 112must be taken. 113Buffers must be externally refcounted or in some other manner 114freed only after last use. 115.Sh HISTORY 116A 117.Nm lwbuf 118implementation first appeared in 119.Dx 2.5 . 120.Sh AUTHORS 121The 122.Nm lwbuf 123implementation and this manpage were written by 124.An Samuel J. Greear . 125