1.\" 2.\" Copyright (c) 2003, 2004 The DragonFly Project. All rights reserved. 3.\" 4.\" This code is derived from software contributed to The DragonFly Project 5.\" by Hiten Pandya <hmp@backplane.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.\" $DragonFly: src/share/man/man9/hash.9,v 1.4 2006/10/19 18:44:00 swildner Exp $ 35.\" 36.Dd May 14, 2004 37.Os 38.Dt HASH 9 39.Sh NAME 40.Nm hash , 41.Nm hashinit , 42.Nm phashinit 43.Nd generic hash table functions for the kernel 44.Sh SYNOPSIS 45.In sys/param.h 46.In sys/systm.h 47.In sys/malloc.h 48.Ft void * 49.Fn hashinit "int elements" "struct malloc_type *type" "u_long *hashmask" 50.Ft void * 51.Fn phashinit "int elements" "struct malloc_type *type" "u_long *nentries" 52.Sh DESCRIPTION 53The kernel hash functions are used for creating a generic hash table. 54.Pp 55The 56.Fn hashinit 57function returns a pointer to a hash table which is sized a 58.Dq "power of two" 59greater or equal to the number of 60.Fa elements 61requested. 62The masking value is stored in 63.Fa hashmask . 64.Pp 65The 66.Fn phashinit 67function returns a pointer to a prime number sized hash table. 68The number of 69.Fa elements 70requested is used to dictate an upper-bound for the size of the 71hash table. 72The final size of the hash table is stored by the function in 73.Fa nentries . 74.Pp 75The 76.Fa type 77argument to both of the above functions is used for keeping track 78of memory allocated for the hash table. 79See the 80.Xr kmalloc 9 81manual page for more information on memory statistics. 82.Sh CODE REFERENCES 83The VFS namecache code is one of many examples for using the 84.Fn hashinit 85function; it is located within the file 86.Pa sys/kern/vfs_cache.c . 87.Pp 88The hostcache code uses the 89.Fn phashinit 90function for creating a prime number sized hash table; it is located 91within the file 92.Pa sys/net/hostcache.c . 93.Pp 94All pathnames in this section are relative to the 95.Dx 96source tree. 97.Sh SEE ALSO 98.Xr tcp 4 , 99.Xr udp 4 , 100.Xr kmalloc 9 , 101.Xr namei 9 102.Sh AUTHORS 103This manual page was written by 104.An Hiten Pandya Aq hmp@backplane.com . 105