.\"	$NetBSD: nsdispatch.3,v 1.2 1999/01/15 12:53:24 lukem Exp $
.\"
.\" Copyright (c) 1997, 1998, 1999 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Luke Mewburn.
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.Dd January 16, 1999
.Dt NSDISPATCH 3
.Os NetBSD
.Sh NAME
.Nm nsdispatch
.Nd name-service switch dispatcher routine
.Sh SYNOPSIS
.Fd #include <nsswitch.h>
.Ft int
.Fn nsdispatch "void *retval" "const ns_dtab dtab[]" "const char *database" "..."
.Sh DESCRIPTION
The
.Fn nsdispatch
function invokes the callback functions specified in 
.Va dtab
in the order given in
.Pa /etc/nsswitch.conf
for the database
.Va database
until a successful entry is found.
.Pp
The return value from the last function invoked is stored at
the location specified in
.Va retval .
.Pp
The optional extra arguments given in
.Va ...
are passed to the appropriate callback function as a variable argument
list of the type
.Va va_list .
.Pp
The format of the
.Va ns_dtab
structure is as follows:
.Bd -literal -offset indent
typedef struct {
	const char *src;
	int (*cb)(void *retval, void *cb_data, va_list ap);
	void *cb_data;
} ns_dtab [];
.Ed
.Pp
For each source type that is implemented, and entry with
.Va src
set to the name of the source,
.Va cb
defined as a function which handles that source, and
.Va cb_data
is used to pass arbritrary data to the callback function.
The last entry in
.Va dtab
should contain
.Dv NULL
values for
.Va src , 
.Va cb ,
and
.Va cb_data .
.Ss Valid source types
Whilst there is support for arbitrary sources, the following
#defines for commonly implementated sources are available:
.Bl -column NS_NISPLUS NISPLUS -offset indent
.Sy #define	value
.It NSSRC_FILES	"files"
.It NSSRC_DNS	"dns"
.It NSSRC_NIS	"nis"
.It NSSRC_NISPLUS	"nisplus"
.It NSSRC_COMPAT	"compat"
.El
.Pp
Refer to
.Xr nsswitch.conf 5
for a complete description of what each source type is.
.Pp
.Ss Callback return values
The callback functions should return one of the following values
depending upon status of the lookup:
.Bl -column NS_NOTFOUND -offset indent
.Sy "Return value"	Status code
.It NS_SUCCESS	success
.It NS_NOTFOUND	notfound
.It NS_UNAVAIL	unavail
.It NS_TRYAGAIN	tryagain
.El
.Pp
Refer to
.Xr nsswitch.conf 5
for a complete description of what each status code is.
.Pp
.Nm
returns the value of the callback that caused the dispatcher to finish,
or NS_NOTFOUND otherwise.
.Sh SEE ALSO
.Xr hesiod 3 ,
.Xr stdarg 3 ,
.Xr ypclnt 3 ,
.Xr nsswitch.conf 5
.Sh HISTORY
The
.Nm
routines first appeared in
.Nx 1.4 .
.Sh AUTHORS
Luke Mewburn
.Aq lukem@netbsd.org
wrote this freely distributable name-service switch implementation,
using ideas from the
.Tn ULTRIX
.Xr svc.conf 5
and
.Tn Solaris
.Xr nsswitch.conf 4
manual pages.
.Sh BUGS
Currently there is no support for dynamically loadable dispatcher functions.
It is anticipated that this will be added in the future in the back-end
without requiring changes to code that invokes
.Fn nsdispatch .