YPCLNT(3) BSD Library Functions Manual YPCLNT(3)
NAME
yp_all, yp_bind, yp_first, yp_get_default_domain, yp_master, yp_match, yp_next, yp_order, yp_unbind, yperr_string, ypprot_err -- Interface to
the YP subsystem
SYNOPSIS
#include <rpc/rpc.h>
#include <rpcsvc/ypclnt.h>
#include <rpcsvc/yp_prot.h>
int
yp_all(char *indomain, char *inmap, struct ypall_callback *incallback);
int
yp_bind(char *dom);
int
yp_first(char *indomain, char *inmap, char **outkey, int *outkeylen, char **outval, int *outvallen);
int
yp_get_default_domain(char **domp);
int
yp_master(char *indomain, char *inmap, char **outname);
int
yp_match(char *indomain, char *inmap, const char *inkey, int inkeylen, 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_order(char *indomain, char *inmap, char *outorder);
void
yp_unbind(char *dom);
char *
yperr_string(int incode);
int
ypprot_err(unsigned int incode);
DESCRIPTION
The ypclnt suite provides an interface to the YP subsystem. For a general description of the YP subsystem, see yp(8).
For all functions, input values begin with in and output values begin with out. Any output values of type char ** should be the addresses of
uninitialized character pointers. Memory will be allocated by the YP client routines using malloc(). This memory can later be freed by the
user if there is no additional need for the data stored there. For outkey and outval, two extra bytes of memory are allocated for a '
' and
' ', which are not reflected in the values of outkeylen or outvallen. All occurrences of indomain and inmap must be non-null, null-termi-
nated strings. All input strings which also have a corresponding length parameter cannot be null unless the corresponding length value is
zero. Such strings need not be null-terminated.
All YP lookup calls (the functions yp_all(), yp_first(), yp_master(), yp_match(), yp_next(), yp_order()) require a YP domain name and a YP
map name. The default domain name may be obtained by calling yp_get_default_domain(), and should thus be used before all other YP calls in a
client program. The value it places outdomain is suitable for use as the indomain parameter to all subsequent YP calls.
In order for YP lookup calls to succeed, the client process must be bound to a YP server process. The client process need not explicitly
bind to the server, as it happens automatically whenever a lookup occurs. The function yp_bind() is provided for a backup strategy, e.g. a
local file, when a YP server process is not available. Each binding uses one socket descriptor on the client process, which may be explic-
itly freed using yp_unbind(), which frees all per-process and per-node resources to bind the domain and marks the domain unbound.
If, during a YP lookup, an RPC failure occurs, the domain used in the lookup is automatically marked unbound and the ypclnt layer retries the
lookup as long as ypbind(8) is running and either the client process cannot bind to a server for the domain specified in the lookup, or RPC
requests to the YP server process fail. If an error is not RPC-related, one of the YP error codes described below is returned and control
given back to the user code.
The ypclnt suite provides the following functionality:
yp_match() Provides the value associated with the given key.
yp_first() Provides the first key-value pair from the given map in the named domain.
yp_next() Provides the next key-value pair in the given map. To obtain the second pair, the inkey value should be the outkey value
provided by the initial call to yp_first(). In the general case, the next key-value pair may be obtained by using the outkey
value from the previous call to yp_next() as the value for inkey.
Of course, the notions of ``first'' and ``next'' are particular to the type of YP map being accessed, and thus there is no
guarantee of lexical order. The only guarantees provided with yp_first() and yp_next(), providing that the same map on the
same server is polled repeatedly until yp_next() returns YPERR_NOMORE, are that all key-value pairs in that map will be
accessed exactly once, and if the entire procedure is repeated, the order will be the same.
If the server is heaviliy loaded or the server fails for some reason, the domain being used may become unbound. If this hap-
pens, and the client process re-binds, the retrieval rules will break: some entries may be seen twice, and others not at all.
For this reason, the function yp_all() provides a better solution for reading all of the entries in a particular map.
yp_all() This function provides a way to transfer an entire map from the server to the client process with a single request. This
transfer uses TCP, unlike all other functions in the ypclnt suite, which use UDP. The entire transaction occurs in a single
RPC request-response. The third argument to this function provides a way to supply the name of a function to process each
key-value pair in the map. Yp_all() returns after the entire transaction is complete, or the foreach function decides that
it does not want any more key-value pairs. The third argument to yp_all() is:
struct ypall_callback *incallback {
int (*foreach)();
char *data;
};
The char *data argument is an opaque pointer for use by the callback function. The foreach function should return non-zero
when it no longer wishes to process key-value pairs, at which time yp_all() returns a value of 0, and is called with the fol-
lowing arguments:
int foreach (
int instatus,
char *inkey,
int inkeylen,
char *inval,
int invallen,
char *indata
);
Where:
instatus Holds one of the return status values described in <rpcsvc/yp_prot.h>: see ypprot_err() below for a function
that will translate YP protocol errors into a ypclnt layer error code as described in <rpcsvc/ypclnt.h>.
inkey, inval The key and value arguments are somewhat different here than described above. In this case, the memory pointed
to by inkey and inval is private to yp_all(), and is overwritten with each subsequent key-value pair, thus the
foreach function should do something useful with the contents of that memory during each iteration. If the
key-value pairs are not terminated with either '
' or ' ' in the map, then they will not be terminated as
such when given to the foreach function, either.
indata This is the contents of the incallback->data element of the callback structure. It is provided as a means to
share state between the foreach function and the user code. Its use is completely optional: cast it to some-
thing useful or simply ignore it.
yp_order() Returns the order number for a map. The order number is updated whenever a map is updated. Clients may use the order number
to check whether they are using the most recent map.
yp_master() Returns the hostname for the machine on which the master YP server process for a map is running.
yperr_string() Returns a pointer to a null-terminated error string that does not contain a '.' or '
'.
ypprot_err() Converts a YP protocol error code to a ypclnt error code suitable for yperr_string().
RETURN VALUES
All functions in the ypclnt suite which are of type int return 0 upon success or one of the following error codes upon failure:
[YPERR_BADARGS] The passed arguments to the function are invalid
[YPERR_BADDB] The YP map that was polled is defective.
[YPERR_DOMAIN] Client process cannot bind to server on this YP domain.
[YPERR_KEY] The key passed does not exist.
[YPERR_MAP] There is no such map in the server's domain.
[YPERR_DOM] The local YP domain is not set.
[YPERR_NOMORE] There are no more records in the queried map.
[YPERR_PMAP] Cannot communicate with portmap.
[YPERR_RESRC] A resource allocation failure occurred.
[YPERR_RPC] An RPC failure has occurred. The domain has been marked unbound.
[YPERR_VERS] Client/server version mismatch. If the server is running version 1 of the YP protocol, yp_all() functionality does not
exist.
[YPERR_BIND] Cannot communicate with ypbind(8).
[YPERR_YPERR] An internal server or client error has occurred.
[YPERR_YPSERV] The client cannot communicate with the YP server process.
SEE ALSO
malloc(3), yp(8), ypbind(8), ypserv(8)
AUTHOR
Theo De Raadt
BSD
October 26, 1994 BSD