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 1.2.2.6 2002/12/29 16:35:39 schweikh Exp $ 27.\" " 28.Dd June 25, 2000 29.Os 30.Dt ACCEPT_FILTER 9 31.Sh NAME 32.Nm accept_filter , 33.Nm accept_filt_add , 34.Nm accept_filt_del , 35.Nm accept_filt_generic_mod_event , 36.Nm accept_filt_get 37.Nd filter incoming connections 38.Sh SYNOPSIS 39.In sys/types.h 40.In sys/socket.h 41.In sys/socketvar.h 42.Ft int 43.Fn accept_filt_add "struct accept_filter *filt" 44.Ft int 45.Fn accept_filt_del "char *name" 46.Ft int 47.Fn accept_filt_generic_mod_event "module_t mod" "int event" "void *data" 48.Ft struct accept_filter * 49.Fn accept_filt_get "char *name" 50.Sh DESCRIPTION 51Accept filters allow an application to request 52that the kernel pre-process incoming connections. 53An accept filter is requested via the 54.Xr setsockopt 2 55system call, passing in an 56.Fa optname 57of 58.Dv SO_ACCEPTFILTER . 59.Sh IMPLEMENTATION NOTES 60A module that wants to be an accept filter 61must provide a struct accept_filter to the system: 62.Bd -literal 63struct accept_filter { 64 char accf_name[16]; 65 void (*accf_callback) 66 __P((struct socket *so, void *arg, int waitflag)); 67 void * (*accf_create) 68 __P((struct socket *so, char *arg)); 69 void (*accf_destroy) 70 __P((struct socket *so)); 71 SLIST_ENTRY(accept_filter) accf_next; /* next on the list */ 72}; 73.Ed 74.Pp 75The module should register it with the function 76.Fn accept_filt_add , 77passing a pointer to a struct accept_filter, allocated with 78.Xr MALLOC 9 79.Pp 80The fields of 81.Fa struct accept_filter 82are as follows: 83.Bl -tag -width accf_callbackXXX 84.It accf_name 85Name of the filter; 86this is how it will be accessed from userland. 87.It accf_callback 88The callback that the kernel will do 89once the connection is established. 90It is the same as a socket upcall 91and will be called when the connection is established 92and whenever new data arrives on the socket, 93unless the callback modifies the socket's flags. 94.It accf_create 95Called whenever a 96.Xr setsockopt 2 97installs the filter onto 98a listening socket. 99.It accf_destroy 100Called whenever the user removes the accept filter on the socket. 101.El 102.Pp 103.Fn accept_filt_del 104passed the same string used in accept_filter.accf_name during registration 105with 106.Fn accept_filt_add , 107the kernel will then disallow and further userland use of the filter. 108.Pp 109.Fn accept_filt_get 110is used internally to locate which accept filter to use via the 111.Fn setsockopt 112syscall. 113.Pp 114.Fn accept_filt_generic_mod_event 115provides a simple way to avoid duplicate 116code for accept filters which don't use 117argument field to load and unload 118themselves. It is a function that can be 119put in the load/unload struct 120for the 121.Fn DECLARE_MODULE 122macro. 123.Sh SEE ALSO 124.Xr setsockopt 2 , 125.Xr accf_data 9 , 126.Xr accf_http 9 , 127.Xr malloc 9 128.Sh HISTORY 129The accept filter mechanism was introduced in 130.Fx 4.0 . 131.Sh AUTHORS 132This manual page was written by 133.An Alfred Perlstein , 134Sheldon Hearn and Jeroen Ruigrok van der Werven. 135The accept filter concept was pioneered by David Filo at Yahoo! 136and refined to be a loadable module system by Alfred Perlstein. 137