Content-type: text/html Man page of ypclnt

ypclnt

Section: C Library Functions (3)
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NAME

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 (NIS) client package  

SYNOPSIS

#include <rpcsvc/ypclnt.h>

int yp_get_default_domain(
        char **outdomain);

int yp_bind(
        char *indomain);

void yp_unbind(
        char *indomain);

int yp_match(
        char *indomain,
        char *inmap,
        char *inkey,
        int inkeylen,
        char **outval,
        int *outvallen);

int yp_first(
        char indomain,
        char *inmap,
        char **outkey,
        int *outkeylen,
        char **outval,
        int *outvallen);

int yp_next(
        char *indomain,
        char *inmap,
        char *inkey,
        int inkeylen,
        char **outkey,
        int *outkeylen,
        char **outval,
        int *outvallen);

int yp_all(
        char *indomain,
        char *inmap,
        struct ypall_callback incallback);

int yp_order(
        char *indomain,
        char *inmap,
        int *outorder);

int yp_master(
        char *indomain,
        char *inmap,
        char **outname);

char *yperr_string(
        int incode);

int ypprot_err(
        unsigned int incode);  

DESCRIPTION

This package of functions provides an interface to the Network Information Service (NIS) data base lookup service. The package can be loaded from the standard library, /lib/libc.a. Refer to ypfiles(4) and ypserv(8) for an overview of NIS, including the definitions of "map" and "domain", and for a description of the servers, data bases, and commands that constitute the NIS application.

All input parameters names begin with "in". Output parameters begin with "out". Output parameters of type char ** should be addresses of uninitialized character pointers. The NIS client package allocates memory using malloc(3). This memory can be freed if the user code has no continuing need for it. The yp_get_default_domain function, however, returns a pointer to thread-specific data. Therefore, the memory cannot be freed by user code. (The contents of that memory are updated with the current default domain on each call.)

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. The indomain and inmap strings must be non-null and null-terminated. String parameters that are accompanied by a count parameter cannot be null, but can point to null strings, with the count parameter indicating this. Counted strings need not be null-terminated.

All functions of type int return 0 if they succeed, or a failure code (YPERR_xxxx) if they do not succeed. Failure codes are described in the ERRORS section of this reference page.

The NIS lookup calls require a map name and a domain name. It is assumed that the client thread knows the name of the map of interest. Client threads 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 NIS services, the client thread must be bound to a NIS server that serves the appropriate domain. The binding is accomplished with yp_bind. Binding need not be done explicitly by user code; it is done automatically whenever a NIS lookup function is called. The yp_bind function can be called directly for processes that make use of a backup strategy in cases when NIS services are not available.

Each binding allocates one client process socket descriptor; each bound domain in each thread requires one socket descriptor. Multiple requests to the same domain from the same thread use that same descriptor. The yp_unbind function is available at the client interface for threads that explicitly manage their socket descriptors while accessing multiple domains. The call to yp_unbind makes the domain unbound, and frees all per-thread and per-node resources used to bind it.

If an RPC failure results upon use of a binding, that domain will be unbound automatically for the thread that encountered the error. At that point, the ypclnt layer will retry forever or until the operation succeeds. This action occurs provided that ypbind is running, and either the client thread cannot bind a server for the proper domain, or RPC requests to the server fail.

The ypbind -S flag allows the system administrator to lock ypbind to a particular domain and set of servers. Up to four servers can be specified. An example of the -S flag follows: /usr/sbin/ypbind -S domain,server1[,server2,server3,server4]

The ypclnt layer will return control to the user code, either with an error code, or with a success code and any results under certain circumstances. For example, control will be returned to the user code when an error is not RPC-related and also when the ypbind function is not running. An additional situation that will cause the return of control is when a bound ypserv process returns any answer (success or failure).

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

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

The yp_next function 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 of next is particular to the structure of the NIS map being processed; 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. Enumerating all entries in a map is accomplished with the yp_all function.

The yp_all function 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. The yp_all function can be used like any other NIS procedure, to identify the map in the normal manner, and to supply the name of a function that will be called to process each key-value pair within the map. Returns from the call to yp_all occur only when the transaction is completed (successfully or unsuccessfully), or when the foreach function decides that it does not 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 invallen; char *indata;

The instatus parameter will hold one of the return status values defined in the rpcsvc/yp_prot.h header file - either YP_TRUE or an error code. (See the discussion of ypprot_err for a function that converts a NIS protocol error code to a ypclnt layer error code.)

The key and value parameters are somewhat different than defined in the syntax 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 will not 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.

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

The yp_order function returns the order number for a map.

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

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

The ypprot_err function 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.  

ERRORS

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 yp 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 */  

FILES

Header file containing ypclnt definitions. Header file defining return status values.  

RELATED INFORMATION

ypfiles(4), ypserv(8)

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Index

NAME
SYNOPSIS
DESCRIPTION
ERRORS
FILES
RELATED INFORMATION

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Time: 02:41:28 GMT, October 02, 2010