YPCLNT(3N)

NAME
ypclnt, yp_get_default_domain, yp_bind, yp_unbind, yp_match, yp_first, yp_next, yp_all, yp_order, yp_master, yperr_string, ypprot_err - network information service client interface

SYNOPSIS
#include <rpcsvc/ypclnt.h>
yp_bind(indomain);
char *indomain;
void yp_unbind(indomain)
char *indomain;
yp_get_default_domain(outdomain);
char **outdomain;
yp_match(indomain, inmap, inkey, inkeylen, outval, outvallen)
char *indomain;
char *inmap;
char *inkey;
int inkeylen;
char **outval;
int *outvallen;
yp_first(indomain, inmap, outkey, outkeylen, outval, outvallen)
char *indomain;
char *inmap;
char **outkey;
int *outkeylen;
char **outval;
int *outvallen;
yp_next(indomain, inmap, inkey, inkeylen, outkey, outkeylen, outval, outvallen);
char *indomain;
char *inmap;
char *inkey;
int inkeylen;
char **outkey;
int *outkeylen;
char **outval;
int *outvallen;
yp_all(indomain, inmap, incallback);
char *indomain;
char *inmap;
struct ypall_callback *incallback;
yp_order(indomain, inmap, outorder);
char *indomain;
char *inmap;
int *outorder;
yp_master(indomain, inmap, outname);
char *indomain;
char *inmap;
char **outname;
char *yperr_string(incode)
int incode;
ypprot_err(incode)
unsigned int incode;

DESCRIPTION
This package of functions provides an interface to the network information service (NIS) network lookup service. The package can be loaded from the standard library, /lib/libc.a. Refer to ypfiles(5) and ypserv(8) for an overview of the network information service, including the definitions of map and domain , and a description of the various servers, databases, and commands that comprise the NIS.

All input parameters names begin with in. Output parameters begin with out. Output parameters of type char ** should be addresses of uninitialized character pointers. Memory is allocated by the NIS client package using malloc(3), and may be freed if the user code has no continuing need for it. For each outkey and outval, two extra bytes of memory are allocated at the end that contain NEWLINE and NULL, respectively, but these two bytes are not reflected in outkeylen or outvallen . indomain and inmap strings must be non-null and null-terminated. String parameters which are accompanied by a count parameter may not be null, but may point to null strings, with the count parameter indicating this. Counted strings need not be null-terminated.

All functions in this package of type int return 0 if they succeed, and a failure code (YPERR_xxxx) otherwise. Failure codes are described under DIAGNOSTICS below.

The NIS lookup calls require a map name and a domain name, at minimum. It is assumed that the client process knows the name of the map of interest. Client processes should fetch the node's default domain by calling yp_get_default_domain() , and use the returned outdomain as the indomain parameter to successive NIS calls.

To use the NIS services, the client process must be ``bound'' to a NIS server that serves the appropriate domain using yp_bind. Binding need not be done explicitly by user code; this is done automatically whenever a NIS lookup function is called. yp_bind can be called directly for processes that make use of a backup strategy (e.g., a local file) in cases when NIS is not available.

Each binding allocates (uses up) one client process socket descriptor; each bound domain costs one socket descriptor. However, multiple requests to the same domain use that same descriptor. yp_unbind() is available at the client interface for processes that explicitly manage their socket descriptors while accessing multiple domains. The call to yp_unbind() make the domain unbound, and free all per-process and per-node resources used to bind it.

If an RPC failure results upon use of a binding, that domain will be unbound automatically. At that point, the ypclnt layer will retry forever or until the operation succeeds, provided that ypbind is running, and either

a)  the client process can't bind a server for the proper domain, or

b)  RPC requests to the server fail.

If an error is not RPC-related, or if ypbind is not running, or if a bound ypserv process returns any answer (success or failure), the ypclnt layer will return control to the user code, either with an error code, or a success code and any results.

yp_match returns the value associated with a passed key. This key must be exact; no pattern matching is available.

yp_first returns the first key-value pair from the named map in the named domain.

yp_next() returns the next key-value pair in a named map. The inkey parameter should be the outkey returned from an initial call to yp_first() (to get the second key-value pair) or the one returned from the nth call to yp_next() (to get the nth + second key-value pair).

The concept of first (and, for that matter, of next) is particular to the structure of the NIS map being processing; there is no relation in retrieval order to either the lexical order within any original (non-NIS) data base, or to any obvious numerical sorting order on the keys, values, or key-value pairs. The only ordering guarantee made is that if the yp_first() function is called on a particular map, and then the yp_next() function is repeatedly called on the same map at the same server until the call fails with a reason of YPERR_NOMORE, every entry in the data base will be seen exactly once. Further, if the same sequence of operations is performed on the same map at the same server, the entries will be seen in the same order.

Under conditions of heavy server load or server failure, it is possible for the domain to become unbound, then bound once again (perhaps to a different server) while a client is running. This can cause a break in one of the enumeration rules; specific entries may be seen twice by the client, or not at all. This approach protects the client from error messages that would otherwise be returned in the midst of the enumeration. The next paragraph describes a better solution to enumerating all entries in a map.

yp_all provides a way to transfer an entire map from server to client in a single request using TCP (rather than UDP as with other functions in this package). The entire transaction take place as a single RPC request and response. You can use yp_all just like any other NIS procedure, identify the map in the normal manner, and supply the name of a function which will be called to process each key-value pair within the map. You return from the call to yp_all only when the transaction is completed (successfully or unsuccessfully), or your ``foreach'' function decides that it doesn't want to see any more key-value pairs.

The third parameter to yp_all is
	struct ypall_callback *incallback {
		int (*foreach)();
		char *data;
	};

The function foreach is called

	foreach(instatus, inkey, inkeylen, inval, invallen, indata);
	int instatus;
	char *inkey;
	int inkeylen;
	char *inval;
	int invalllen;
	char *indata;

The instatus parameter will hold one of the return status values defined in <rpcsvc/yp_prot.h> — either YP_TRUE, YP_NOMORE or an error code. (See ypprot_err , below, for a function which converts a NIS protocol error code to a ypclnt layer error code.)

The key and value parameters are somewhat different than defined in the synopsis section above. First, the memory pointed to by the inkey and inval parameters is private to the yp_all function, and is overwritten with the arrival of each new key-value pair. It is the responsibility of the foreach function to do something useful with the contents of that memory, but it does not own the memory itself. Key and value objects presented to the foreach function look exactly as they do in the server's map — if they were not newline-terminated or null-terminated in the map, they won't be here either.

The indata parameter is the contents of the incallback->data element passed to yp_all . The data element of the callback structure may be used to share state information between the foreach function and the mainline code. Its use is optional, and no part of the NIS client package inspects its contents — cast it to something useful, or ignore it as you see fit.

The foreach function is a Boolean. It should return zero to indicate that it wants to be called again for further received key-value pairs, or non-zero to stop the flow of key-value pairs. If foreach returns a non-zero value, it is not called again; the functional value of yp_all is then 0.

yp_order returns the order number for a map.

yp_master returns the machine name of the master NIS server for a map.

yperr_string returns a pointer to an error message string that is null-terminated but contains no period or newline.

ypprot_err takes a NIS protocol error code as input, and returns a ypclnt layer error code, which may be used in turn as an input to yperr_string .

FILES
/usr/include/rpcsvc/ypclnt.h
/usr/include/rpcsvc/yp_prot.h

SEE ALSO
ypfiles(5), ypserv(8),

DIAGNOSTICS
All integer functions return 0 if the requested operation is successful, or one of the following errors if the operation fails.

    #define YPERR_BADARGS	1	/* args to function are bad */
    #define YPERR_RPC	2	/* RPC failure - domain has been unbound */
    #define YPERR_DOMAIN	3	/* can't bind to server on this domain */
    #define YPERR_MAP	4	/* no such map in server's domain */
    #define YPERR_KEY	5	/* no such key in map */
    #define YPERR_YPERR	6	/* internal NIS server or client error */
    #define YPERR_RESRC	7	/* resource allocation failure */
    #define YPERR_NOMORE	8	/* no more records in map database */
    #define YPERR_PMAP	9	/* can't communicate with portmapper */
    #define YPERR_YPBIND	10	/* can't communicate with ypbind */
    #define YPERR_YPSERV	11	/* can't communicate with ypserv */
    #define YPERR_NODOM	12	/* local domain name not set */