358 lines
9.1 KiB
Groff
358 lines
9.1 KiB
Groff
.\" $NetBSD: nsdispatch.3,v 1.22 2004/09/29 09:20:19 wiz Exp $
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.\"
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.\" Copyright (c) 1997, 1998, 1999, 2004 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Luke Mewburn; and by Jason R. Thorpe.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd September 28, 2004
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.Dt NSDISPATCH 3
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.Os
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.Sh NAME
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.Nm nsdispatch
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.Nd name-service switch dispatcher routine
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In nsswitch.h
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.Ft int
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.Fo nsdispatch
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.Fa "void *retval"
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.Fa "const ns_dtab dtab[]"
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.Fa "const char *database"
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.Fa "const char *method"
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.Fa "const ns_src defaults[]"
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.Fa "..."
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.Fc
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.Sh DESCRIPTION
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The
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.Fn nsdispatch
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function invokes the callback functions specified in
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.Va dtab
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in the order given in
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.Pa /etc/nsswitch.conf
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for the database
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.Va database
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until the action criteria for a source of that database is fulfilled.
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.Pp
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.Va retval
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is passed to each callback function to modify as necessary
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(to pass back to the caller of
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.Fn nsdispatch ) .
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.Pp
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Each callback has the function signature described by the typedef:
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.Pp
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.Bd -ragged -offset indent
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.Ft typedef int
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.Fn \*(lp*nss_method\*(rp "void *retval" "void *cb_data" "va_list ap" ;
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.Ed
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.Pp
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.Va dtab
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is an array of
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.Va ns_dtab
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structures, which have the following format:
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.Bd -literal -offset indent
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typedef struct {
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const char *src;
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nss_method cb;
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void *cb_data;
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} ns_dtab;
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.Ed
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.Pp
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.Bd -ragged -offset indent
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The
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.Va dtab
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array should consist of one entry for each source type that has a
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static implementation,
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with
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.Va src
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as the name of the source,
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.Va cb
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as a function which handles that source, and
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.Va cb_data
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as a pointer to arbitrary data to be passed to the callback.
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The last entry in
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.Va dtab
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should contain
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.Dv NULL
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values for
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.Va src ,
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.Va cb ,
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and
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.Va cb_data .
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.Ed
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.Pp
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Callbacks may also be provided by dynamically-loaded modules, in which
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case they are selected using the
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.Va database
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and
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.Va method
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arguments in addition to the configured source.
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.Va method
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is usually the name of the function calling
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.Fn nsdispatch .
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Note that the callbacks provided by
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.Va dtab
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take priority over those implemented in dynamically-loaded modules in the
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event of a conflict.
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.Pp
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.Va defaults
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contains a list of default sources to try in the case of
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a missing or corrupt
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.Xr nsswitch.conf 5 ,
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or if there isn't a relevant entry for
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.Va database .
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It is an array of
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.Va ns_src
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structures, which have the following format:
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.Bd -literal -offset indent
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typedef struct {
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const char *src;
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u_int32_t flags;
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} ns_src;
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.Ed
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.Pp
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.Bd -ragged -offset indent
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The
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.Va defaults
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array should consist of one entry for each source to consult by default
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indicated by
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.Va src ,
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and
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.Va flags
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set to the desired behavior
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(usually
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.Dv NS_SUCCESS ;
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refer to
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.Sx Callback return values
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for more information).
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The last entry in
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.Va defaults
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should have
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.Va src
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set to
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.Dv NULL
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and
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.Va flags
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set to 0.
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.Pp
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Some invokers of
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.Fn nsdispatch
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(such as
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.Xr setgrent 3 )
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need to force all methods to be invoked,
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irrespective of the action criteria listed in
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.Xr nsswitch.conf 5 .
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This can be achieved by adding
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.Dv NS_FORCEALL
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to
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.Va defaults[0].flags
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before invoking
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.Fn nsdispatch .
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The return value of
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.Fn nsdispatch
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will be the result of the final callback method invoked.
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.Pp
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For convenience, a global variable defined as:
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.Dl extern const ns_src __nsdefaultsrc[];
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exists which contains a single default entry for
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.Sq files
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for use by callers which don't require complicated default rules.
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.Ed
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.Pp
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.Sq Va ...
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are optional extra arguments, which
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are passed to the appropriate callback function as a variable argument
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list of the type
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.Va va_list .
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.Ss Dynamically-loaded module interface
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The
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.Fn nsdispatch
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function loads callback modules from the run-time link-editor's search
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path using the following naming convention:
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.Bd -literal -offset indent
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nss_\*[Lt]source\*[Gt].so.\*[Lt]version\*[Gt]
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.Ed
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.Bl -tag -width XversionX -offset indent
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.It Aq source
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The source that the module implements.
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.It Aq version
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The
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.Nm nsdispatch
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module interface version, which is defined by the integer
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.Dv NSS_MODULE_INTERFACE_VERSION ,
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which has the value 0.
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.El
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.Pp
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When a module is loaded,
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.Fn nsdispatch
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looks for and calls the following function in the module:
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.Pp
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.Bd -ragged -offset indent
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.Ft ns_mtab *
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.Fn nss_module_register "const char *source" "u_int *nelems" \
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"nss_module_unregister_fn *unreg" ;
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.Ed
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.Pp
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.Bl -tag -width source
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.It Va source
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The name of the source that the module implements, as used by
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.Fn nsdispatch
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to construct the module's name.
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.It Va nelems
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A pointer to an unsigned integer that
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.Fn nss_module_register
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should set to the number of elements in the
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.Va ns_mtab
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array returned by
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.Fn nss_module_register .
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.It Va unreg
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A pointer to a function pointer that
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.Fn nss_module_resgister
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can optionally set to a function to be invoked when the module is
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unloaded.
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.El
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.Pp
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The unregister function signature is described by the typedef:
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.Pp
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.Bd -ragged -offset indent
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.Ft typedef void
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.Fn \*(lp*nss_module_unregister_fn\*(rp "ns_mtab *mtab" "u_int nelems" ;
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.Ed
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.Pp
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.Fn nss_module_register
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returns an array of
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.Va ns_mtab
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structures, which have the following format:
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.Bd -literal -offset indent
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typedef struct {
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const char *database;
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const char *name;
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nss_method method;
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void *mdata;
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} ns_mtab;
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.Ed
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.Pp
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.Bd -ragged -offset indent
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The
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.Va mtab
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array should consist of one entry for each method that is implemented,
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with
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.Va database
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as the name of the database,
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.Va name
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as the name of the method,
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.Va method
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as the callback that implements the method, and
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.Va mdata
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as a pointer to arbitrary data to be passed to the callback.
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.Ed
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.Ss Valid source types
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While there is support for arbitrary sources, the following
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#defines for commonly implemented sources are provided:
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.Bl -column NSSRC_COMPAT COMPAT -offset indent
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.Sy #define value
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.It NSSRC_FILES "files"
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.It NSSRC_DNS "dns"
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.It NSSRC_NIS "nis"
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.It NSSRC_COMPAT "compat"
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.El
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.Pp
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Refer to
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.Xr nsswitch.conf 5
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for a complete description of what each source type is.
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.Ss Valid database types
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While there is support for arbitrary databases, the following
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#defines for currently implemented system databases are provided:
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.Bl -column NSDB_NETGROUP NETGROUP -offset indent
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.Sy #define value
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.It NSDB_HOSTS "hosts"
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.It NSDB_GROUP "group"
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.It NSDB_NETGROUP "netgroup"
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.It NSDB_NETWORKS "networks"
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.It NSDB_PASSWD "passwd"
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.It NSDB_SHELLS "shells"
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.El
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.Pp
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Refer to
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.Xr nsswitch.conf 5
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for a complete description of what each database is.
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.Ss Callback return values
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The callback functions should return one of the following values
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depending upon status of the lookup:
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.Bl -column NS_NOTFOUND -offset indent
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.Sy "Return value" Status code
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.It NS_SUCCESS success
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.It NS_NOTFOUND notfound
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.It NS_UNAVAIL unavail
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.It NS_TRYAGAIN tryagain
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.El
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.Pp
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Refer to
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.Xr nsswitch.conf 5
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for a complete description of what each status code is.
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.Pp
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.Nm
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returns the value of the callback that caused the dispatcher to finish,
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or
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.Dv NS_NOTFOUND
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otherwise.
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.Sh SEE ALSO
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.Xr ld.elf_so 1 ,
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.Xr hesiod 3 ,
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.Xr stdarg 3 ,
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.Xr ypclnt 3 ,
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.Xr nsswitch.conf 5
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.Sh HISTORY
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The
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.Nm
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routines first appeared in
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.Nx 1.4 .
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Support for dynamically-loaded modules first appeared in
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.Nx 3.0 .
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.Sh AUTHORS
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Luke Mewburn
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.Aq lukem@NetBSD.org
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wrote this freely distributable name-service switch implementation,
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using ideas from the
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.Tn ULTRIX
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.Xr svc.conf 5
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and
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.Tn Solaris
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.Xr nsswitch.conf 4
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manual pages.
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Support for dynamically-loaded modules was added by Jason Thorpe
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.Aq thorpej@NetBSD.org ,
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based on code developed by the
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.Fx
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Project.
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