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.\" $DragonFly: src/share/man/man9/accept_filter.9,v 1.2 2003/06/17 04:37:01 dillon 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/socket.h 42.In sys/socketvar.h 43.Ft int 44.Fn accept_filt_add "struct accept_filter *filt" 45.Ft int 46.Fn accept_filt_del "char *name" 47.Ft int 48.Fn accept_filt_generic_mod_event "module_t mod" "int event" "void *data" 49.Ft struct accept_filter * 50.Fn accept_filt_get "char *name" 51.Sh DESCRIPTION 52Accept filters allow an application to request 53that the kernel pre-process incoming connections. 54An accept filter is requested via the 55.Xr setsockopt 2 56system call, passing in an 57.Fa optname 58of 59.Dv SO_ACCEPTFILTER . 60.Sh IMPLEMENTATION NOTES 61A module that wants to be an accept filter 62must provide a struct accept_filter to the system: 63.Bd -literal 64struct accept_filter { 65 char accf_name[16]; 66 void (*accf_callback) 67 __P((struct socket *so, void *arg, int waitflag)); 68 void * (*accf_create) 69 __P((struct socket *so, char *arg)); 70 void (*accf_destroy) 71 __P((struct socket *so)); 72 SLIST_ENTRY(accept_filter) accf_next; /* next on the list */ 73}; 74.Ed 75.Pp 76The module should register it with the function 77.Fn accept_filt_add , 78passing a pointer to a struct accept_filter, allocated with 79.Xr MALLOC 9 80.Pp 81The fields of 82.Fa struct accept_filter 83are as follows: 84.Bl -tag -width accf_callbackXXX 85.It accf_name 86Name of the filter; 87this is how it will be accessed from userland. 88.It accf_callback 89The callback that the kernel will do 90once the connection is established. 91It is the same as a socket upcall 92and will be called when the connection is established 93and whenever new data arrives on the socket, 94unless the callback modifies the socket's flags. 95.It accf_create 96Called whenever a 97.Xr setsockopt 2 98installs the filter onto 99a listening socket. 100.It accf_destroy 101Called whenever the user removes the accept filter on the socket. 102.El 103.Pp 104.Fn accept_filt_del 105passed the same string used in accept_filter.accf_name during registration 106with 107.Fn accept_filt_add , 108the kernel will then disallow and further userland use of the filter. 109.Pp 110.Fn accept_filt_get 111is used internally to locate which accept filter to use via the 112.Fn setsockopt 113syscall. 114.Pp 115.Fn accept_filt_generic_mod_event 116provides a simple way to avoid duplicate 117code for accept filters which don't use 118argument field to load and unload 119themselves. It is a function that can be 120put in the load/unload struct 121for the 122.Fn DECLARE_MODULE 123macro. 124.Sh SEE ALSO 125.Xr setsockopt 2 , 126.Xr accf_data 9 , 127.Xr accf_http 9 , 128.Xr malloc 9 129.Sh HISTORY 130The accept filter mechanism was introduced in 131.Fx 4.0 . 132.Sh AUTHORS 133This manual page was written by 134.An Alfred Perlstein , 135Sheldon Hearn and Jeroen Ruigrok van der Werven. 136The accept filter concept was pioneered by David Filo at Yahoo! 137and refined to be a loadable module system by Alfred Perlstein. 138