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.Dd April 4, 2010
.Dt NSDISPATCH 3
.Os
.Sh NAME
.Nm nsdispatch
.Nd name-service switch dispatcher routine
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In stdarg.h
.In nsswitch.h
.Ft int
.Fo nsdispatch
.Fa "void *retval"
.Fa "const ns_dtab dtab[]"
.Fa "const char *database"
.Fa "const char *method_name"
.Fa "const ns_src defaults[]"
.Fa "..."
.Fc
.Sh DESCRIPTION
The
.Fn nsdispatch
function invokes the methods specified in
.Va dtab
in the order given by
.Xr nsswitch.conf 5
for the database
.Va database
until a successful entry is found.
.Pp
.Va retval
is passed to each method to modify as necessary, to pass back results to
the caller of
.Fn nsdispatch .
.Pp
Each method has the function signature described by the typedef:
.Pp
.Ft typedef int
.Fn \*(lp*nss_method\*(rp "void *retval" "void *mdata" "va_list *ap" ;
.Pp
.Va dtab
is an array of
.Va ns_dtab
structures, which have the following format:
.Bd -literal -offset indent
typedef struct _ns_dtab {
	const char	*src;
	nss_method	 method;
	void		*mdata;
} ns_dtab;
.Ed
.Pp
The
.Fa dtab
array should consist of one entry for each source type that is
implemented, with
.Va src
as the name of the source,
.Va method
as a function which handles that source, and
.Va mdata
as a handle on arbitrary data to be passed to the method.
The last entry in
.Va dtab
should contain
.Dv NULL
values for
.Va src ,
.Va method ,
and
.Va mdata .
.Pp
Additionally, methods may be implemented in NSS modules, in
which case they are selected using the
.Fa database
and
.Fa method_name
arguments along with the configured source.
(The methods supplied via
.Fa dtab
take priority over those implemented in NSS modules in the event
of a conflict.)
.Pp
.Va defaults
contains a list of default sources to try if
.Xr nsswitch.conf 5
is missing or corrupted, or if there is no 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 _ns_src {
	const char	*src;
	uint32_t	 flags;
} ns_src;
.Ed
.Pp
The
.Fa defaults
array should consist of one entry for each source to be configured by
default indicated by
.Va src ,
and
.Va flags
set to the criterion desired
(usually
.Dv NS_SUCCESS ;
refer to
.Sx Method 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:
.Pp
.Dl extern const ns_src __nsdefaultsrc[];
.Pp
exists which contains a single default entry for the source
.Sq files
that may be used by callers which do not require complicated default
rules.
.Pp
.Sq Va ...
are optional extra arguments, which are passed to the appropriate method
as a variable argument list of the type
.Vt va_list .
.Ss Valid source types
While there is support for arbitrary sources, the following
#defines for commonly implemented sources are available:
.Bl -column NSSRC_COMPAT compat -offset indent
.It Sy "#define	value"
.It Dv NSSRC_FILES Ta  \&"files\&"
.It Dv NSSRC_DB Ta \&"db\&"
.It Dv NSSRC_DNS Ta \&"dns\&"
.It Dv NSSRC_NIS Ta \&"nis\&"
.It Dv NSSRC_COMPAT Ta \&"compat\&"
.El
.Pp
Refer to
.Xr nsswitch.conf 5
for a complete description of what each source type is.
.Ss Method return values
The
.Vt nss_method
functions must return one of the following values depending upon status
of the lookup:
.Bl -column "Return value" "Status code"
.It Sy "Return value	Status code"
.It Dv NS_SUCCESS Ta success
.It Dv NS_NOTFOUND Ta notfound
.It Dv NS_UNAVAIL Ta unavail
.It Dv NS_TRYAGAIN Ta tryagain
.It Dv NS_RETURN Ta -none-
.El
.Pp
Refer to
.Xr nsswitch.conf 5
for a complete description of each status code.
.Pp
The
.Fn nsdispatch
function returns the value of the method that caused the dispatcher to
terminate, or
.Dv NS_NOTFOUND
otherwise.
.Sh NOTES
.Fx Ns 's
.Lb libc
provides stubs for compatibility with NSS modules
written for the
.Tn GNU
C Library
.Nm nsswitch
interface.
However, these stubs only support the use of the
.Dq Li passwd
and
.Dq Li group
databases.
.Sh SEE ALSO
.Xr hesiod 3 ,
.Xr stdarg 3 ,
.Xr nsswitch.conf 5 ,
.Xr yp 8
.Sh HISTORY
The
.Fn nsdispatch
function first appeared in
.Fx 5.0 .
It was imported from the
.Nx
Project,
where it appeared first in
.Nx 1.4 .
Support for NSS modules first appeared in
.Fx 5.1 .
.Sh AUTHORS
Luke Mewburn
.Aq lukem@netbsd.org
wrote this freely-distributable name-service switch implementation,
using ideas from the
.Tn ULTRIX
svc.conf(5)
and
.Tn Solaris
nsswitch.conf(4)
manual pages.
The
.Fx
Project
added the support for threads and NSS modules, and normalized the uses
of
.Fn nsdispatch
within the standard C library.