1.\" 2.\" Copyright (c) 2000 Alfred Perlstein 3.\" 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR 16.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT, 19.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25.\" 26.\" $FreeBSD: src/share/man/man9/accept_filter.9,v 1.13 2004/06/16 08:33:57 ru Exp $ 27.\" $DragonFly: src/share/man/man9/accept_filter.9,v 1.6 2007/09/26 19:18:30 swildner Exp $ 28.\" 29.Dd June 25, 2000 30.Os 31.Dt ACCEPT_FILTER 9 32.Sh NAME 33.Nm accept_filter , 34.Nm accept_filt_add , 35.Nm accept_filt_del , 36.Nm accept_filt_generic_mod_event , 37.Nm accept_filt_get 38.Nd filter incoming connections 39.Sh SYNOPSIS 40.In sys/types.h 41.In sys/module.h 42.In sys/socket.h 43.Fd #define ACCEPT_FILTER_MOD 44.In sys/socketvar.h 45.Ft int 46.Fn accept_filt_add "struct accept_filter *filt" 47.Ft int 48.Fn accept_filt_del "char *name" 49.Ft int 50.Fn accept_filt_generic_mod_event "module_t mod" "int event" "void *data" 51.Ft struct accept_filter * 52.Fn accept_filt_get "char *name" 53.Sh DESCRIPTION 54Accept filters allow an application to request 55that the kernel pre-process incoming connections. 56An accept filter is requested via the 57.Xr setsockopt 2 58system call, passing in an 59.Fa optname 60of 61.Dv SO_ACCEPTFILTER . 62.Sh IMPLEMENTATION NOTES 63A module that wants to be an accept filter 64must provide a 65.Vt "struct accept_filter" 66to the system: 67.Bd -literal 68struct accept_filter { 69 char accf_name[16]; 70 void (*accf_callback)(struct socket *so, void *arg, int waitflag); 71 void * (*accf_create)(struct socket *so, char *arg); 72 void (*accf_destroy)(struct socket *so); 73 SLIST_ENTRY(accept_filter) accf_next; /* next on the list */ 74}; 75.Ed 76.Pp 77The module should register it with the function 78.Fn accept_filt_add , 79passing a pointer to a 80.Vt "struct accept_filter" , 81allocated with 82.Xr kmalloc 9 83.Pp 84The fields of 85.Vt "struct accept_filter" 86are as follows: 87.Bl -tag -width ".Va accf_callback" 88.It Fa accf_name 89Name of the filter; 90this is how it will be accessed from userland. 91.It Fa accf_callback 92The callback that the kernel will do 93once the connection is established. 94It is the same as a socket upcall 95and will be called when the connection is established 96and whenever new data arrives on the socket, 97unless the callback modifies the socket's flags. 98.It Fa accf_create 99Called whenever a 100.Xr setsockopt 2 101installs the filter onto 102a listening socket. 103.It Fa accf_destroy 104Called whenever the user removes the accept filter on the socket. 105.El 106.Pp 107The 108.Fn accept_filt_del 109function passed the same string used in 110.Fa accept_filter.accf_name 111during registration with 112.Fn accept_filt_add , 113the kernel will then disallow and further userland use of the filter. 114.Pp 115The 116.Fn accept_filt_get 117function is used internally to locate which accept filter to use via the 118.Xr setsockopt 2 119system call. 120.Pp 121The 122.Fn accept_filt_generic_mod_event 123function provides a simple way to avoid duplication of code 124for accept filters which do not use the argument field to load 125and unload themselves. 126This function can be used in the 127.Vt moduledata_t 128struct for the 129.Xr DECLARE_MODULE 9 130macro. 131.Sh SEE ALSO 132.Xr setsockopt 2 , 133.Xr accf_data 9 , 134.Xr accf_http 9 , 135.Xr kmalloc 9 136.Sh HISTORY 137The accept filter mechanism was introduced in 138.Fx 4.0 . 139.Sh AUTHORS 140.An -nosplit 141This manual page was written by 142.An Alfred Perlstein , 143.An Sheldon Hearn 144and 145.An Jeroen Ruigrok van der Werven . 146.Pp 147The accept filter concept was pioneered by 148.An David Filo 149at Yahoo!\& 150and refined to be a loadable module system by 151.An Alfred Perlstein . 152