Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
NSDISPATCH(3)	       FreeBSD Library Functions Manual		 NSDISPATCH(3)

     nsdispatch	-- name-service	switch dispatcher routine

     Standard C	Library	(libc, -lc)

     #include <sys/types.h>
     #include <stdarg.h>
     #include <nsswitch.h>

     nsdispatch(void *retval, const ns_dtab dtab[], const char *database,
	 const char *method_name, const	ns_src defaults[], ...);

     The nsdispatch() function invokes the methods specified in	dtab in	the
     order given by nsswitch.conf(5) for the database database until a suc-
     cessful entry is found.

     retval is passed to each method to	modify as necessary, to	pass back re-
     sults to the caller of nsdispatch().

     Each method has the function signature described by the typedef:

     typedef int (*nss_method)(void *retval, void *mdata, va_list *ap);

     dtab is an	array of ns_dtab structures, which have	the following format:

	   typedef struct _ns_dtab {
		   const char	   *src;
		   nss_method	    method;
		   void		   *mdata;
	   } ns_dtab;

     The dtab array should consist of one entry	for each source	type that is
     implemented, with src as the name of the source, method as	a function
     which handles that	source,	and mdata as a handle on arbitrary data	to be
     passed to the method.  The	last entry in dtab should contain NULL values
     for src, method, and mdata.

     Additionally, methods may be implemented in NSS modules, in which case
     they are selected using the database and method_name arguments along with
     the configured source.  Modules must use source names different from the
     built-in ones.

     defaults contains a list of default sources to try	if nsswitch.conf(5) is
     missing or	corrupted, or if there is no relevant entry for	database.  It
     is	an array of ns_src structures, which have the following	format:

	   typedef struct _ns_src {
		   const char	   *src;
		   uint32_t	    flags;
	   } ns_src;

     The defaults array	should consist of one entry for	each source to be con-
     figured by	default	indicated by src, and flags set	to the criterion de-
     sired (usually NS_SUCCESS;	refer to Method	return values for more infor-
     mation).  The last	entry in defaults should have src set to NULL and
     flags set to 0.

     For convenience, a	global variable	defined	as:

	   extern const	ns_src __nsdefaultsrc[];

     exists which contains a single default entry for the source `files' that
     may be used by callers which do not require complicated default rules.

     `...' are optional	extra arguments, which are passed to the appropriate
     method as a variable argument list	of the type va_list.

   Valid source	types
     While there is support for	arbitrary sources, the following #defines for
     commonly implemented sources are available:

	   #define	   value
	   NSSRC_FILES	   "files"
	   NSSRC_DB	   "db"
	   NSSRC_DNS	   "dns"
	   NSSRC_NIS	   "nis"
	   NSSRC_COMPAT	   "compat"

     Refer to nsswitch.conf(5) for a complete description of what each source
     type is.

   Method return values
     The nss_method functions must return one of the following values depend-
     ing upon status of	the lookup:

     Return value    Status code
     NS_SUCCESS	     success
     NS_NOTFOUND     notfound
     NS_UNAVAIL	     unavail
     NS_TRYAGAIN     tryagain
     NS_RETURN	     -none-

     Refer to nsswitch.conf(5) for a complete description of each status code.

     The nsdispatch() function returns the value of the	method that caused the
     dispatcher	to terminate, or NS_NOTFOUND otherwise.

     FreeBSD's Standard	C Library (libc, -lc) provides stubs for compatibility
     with NSS modules written for the GNU C Library nsswitch interface.	 How-
     ever, these stubs only support the	use of the "passwd" and	"group"	data-

     hesiod(3),	stdarg(3), nsswitch.conf(5), yp(8)

     The nsdispatch() function first appeared in FreeBSD 5.0.  It was imported
     from the NetBSD Project, where it appeared	first in NetBSD	1.4.  Support
     for NSS modules first appeared in FreeBSD 5.1.

     Luke Mewburn <> wrote this	freely-distributable name-ser-
     vice switch implementation, using ideas from the ULTRIX svc.conf(5) and
     Solaris nsswitch.conf(4) manual pages.  The FreeBSD Project added the
     support for threads and NSS modules, and normalized the uses of
     nsdispatch() within the standard C	library.

FreeBSD	13.0		       October 15, 2018			  FreeBSD 13.0


Want to link to this manual page? Use this URL:

home | help