NSDISPATCH(3)

NAME
nsdispatch - name-service switch dispatcher routine

LIBRARY
libc

SYNOPSIS
#include <nsswitch.h>
int
nsdispatch(void *retval, const ns_dtab dtab[], const char *database, const char *method, const ns_src defaults[], ...);

DESCRIPTION
The nsdispatch() function invokes the callback functions specified in dtab in the order given in /etc/nsswitch.conf for the database database until a successful entry is found.

retval is passed to each callback function to modify as necessary (to pass back to the caller of nsdispatch())

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

    typedef struct {
    	const char *src;
    	int (*cb)(void *retval, void *cb_data, va_list ap);
    	void *cb_data;
    } ns_dtab;

For each source type that is implemented, an entry with src set to the name of the source, cb defined as a function which handles that source, and cb_data is used to pass arbritrary data to the callback function. The last entry in dtab should contain NULL values for src, cb, and cb_data.

method is usually the name of the function calling nsdispatch(). When dynamic loading is supported, a symbol constructed from database, the current source, and method will be used as the name to invoke the dynamically loaded function.

defaults contains a list of default sources to try in the case of a missing or corrupt nsswitch.conf(5), or if there isn't a relevant entry for database. It is an array of ns_src structures, which have the following format:

    typedef struct {
    	const char *src;
    	u_int32_t flags;
    } ns_src;

For each default source type, an entry with src set to the name of the source, and flags set to the relevant flags (usually NS_SUCCESS; refer to Callback 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 ‘files’ for use by callers which don't require complicated default rules.

‘...’ are optional extra arguments, which are passed to the appropriate callback function as a variable argument list of the type va_list.

  Valid source types
Whilst there is support for arbitrary sources, the following #defines for commonly implementated sources are available:
#define value
NSSRC_FILES files
NSSRC_DNS dns
NSSRC_NIS nis
NSSRC_COMPAT compat

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

  Callback return values
The callback functions should return one of the following values depending upon status of the lookup:
Return value Status code
NS_SUCCESS success
NS_NOTFOUND notfound
NS_UNAVAIL unavail
NS_TRYAGAIN tryagain

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

nsdispatch returns the value of the callback that caused the dispatcher to finish, or NS_NOTFOUND otherwise.

SEE ALSO
hesiod(3), stdarg(3), ypclnt(3), nsswitch.conf(5)

HISTORY
The nsdispatch routines first appeared in NetBSD 1.4.

AUTHORS
Luke Mewburn <lukem@netbsd.org> wrote this freely distributable name-service switch implementation, using ideas from the ULTRIX svc.conf(5) and Solaris nsswitch.conf(4) manual pages.

BUGS
The nsdispatch routines are not thread safe. This will be rectified in the future.

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 nsdispatch().