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 gen‐
eral 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 ‘\n’ and
‘\0’, which are not reflected in the values of outkeylen or outvallen.
All occurrences of indomain and inmap must be non-null, null-terminated
strings. All input strings which also have a corresponding length param‐
eter 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 explicitly 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 can‐
not 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 par‐
ticular to the type of YP map being accessed, and thus
there is no guarantee of lexical order. The only guaran‐
tees 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 happens, 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 func‐
tion 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 func‐
tions 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 following 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
‘\n’ or ‘\0’ 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 something 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 ‘\n’.
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 run‐
ning version 1 of the YP protocol, yp_all() functional‐
ity 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 ALSOmalloc(3), yp(8), ypbind(8), ypserv(8)AUTHOR
Theo De Raadt
BSD October 26, 1994 BSD
