nsdispatch man page on FreeBSD

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NSDISPATCH(3)		 BSD 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
     results 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.  (The methods supplied via dtab take priority over
     those implemented in NSS modules in the event of a conflict.)

     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;
		   u_int32_t	    flags;
	   } ns_src;

	   The defaults array should consist of one entry for each source to
	   be configured by default indicated by src, and flags set to the
	   criterion desired (usually NS_SUCCESS; refer to Method return
	   values for more information).  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 ⟨lukem@netbsd.org⟩ 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.

BSD				 April 4, 2010				   BSD

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