nsdispatch.3

Newlib 嵌入式 C库 标准实现代码

.\"	$NetBSD: nsdispatch.3,v 1.8 1999/03/22 19:44:53 garbled Exp $
.\"	$FreeBSD: src/lib/libc/net/nsdispatch.3,v 1.5 2001/10/01 16:08:56 ru Exp $
.\"
.\" Copyright (c) 1997, 1998, 1999 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Luke Mewburn.
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.Dd January 19, 1999
.Dt NSDISPATCH 3
.Os
.Sh NAME
.Nm nsdispatch
.Nd name-service switch dispatcher routine
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In nsswitch.h
.Ft int
.Fo nsdispatch
.Fa "void *retval"
.Fa "const ns_dtab dtab[]"
.Fa "const char *database"
.Fa "const char *method"
.Fa "const ns_src defaults[]"
.Fa "..."
.Fc
.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
.Va retval
is passed to each callback function to modify as necessary
(to pass back to the caller of
.Fn nsdispatch )
.Pp
.Va dtab
is an array of
.Va ns_dtab
structures, which have the following format:
.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
.Bd -ragged -offset indent
For each source type that is implemented, an 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 .
.Ed
.Pp
.Va method
is usually the name of the function calling
.Fn nsdispatch .
When dynamic loading is supported, a symbol constructed from
.Va database ,
the current source, and
.Va method
will be used as the name to invoke the dynamically loaded function.
.Pp
.Va defaults
contains a list of default sources to try in the case of
a missing or corrupt
.Xr nsswitch.conf 5 ,
or if there isn't a relevant entry for
.Va database .
It is an array of
.Va ns_src
structures, which have the following format:
.Bd -literal -offset indent
typedef struct {
	const char *src;
	u_int32_t flags;
} ns_src;
.Ed
.Pp
.Bd -ragged -offset indent
For each default source type, an entry with
.Va src
set to the name of the source, and
.Va flags
set to the relevant flags
(usually
.Dv NS_SUCCESS ;
refer to
.Sx Callback return values
for more information).
The last entry in
.Va defaults
should have
.Va src
set to
.Dv NULL
and
.Va flags
set to 0.
.Pp
For convenience, a global variable defined as:
.Dl extern const ns_src __nsdefaultsrc[];
exists which contains a single default entry for
.Sq files
for use by callers which don't require complicated default rules.
.Ed
.Pp
.Sq Va ...
are optional extra arguments, which
are passed to the appropriate callback function as a variable argument
list of the type
.Va va_list .
.Ss Valid source types
Whilst there is support for arbitrary sources, the following
#defines for commonly implementated sources are available:
.Bl -column NS_COMPAT COMPAT -offset indent
.It Sy "#define	value"
.It "NSSRC_FILES	""files"""
.It "NSSRC_DNS	""dns"""
.It "NSSRC_NIS	""nis"""
.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
.It 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
.Fx 4.1 .
They were imported from the
.Nx
Project,
where they appeared first in
.Nx 1.4 .
.Sh AUTHORS
Luke Mewburn
.Aq [e-mail]
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
The
.Nm
routines are not thread safe.
This will be rectified in the future.
.Pp
Currently there is no support for dynamically loadable dispatcher callback
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 .