ypclnt(3)ypclnt(3)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 Infor‐
mation Service (NIS) client package
SYNOPSIS
#include <rpcsvc/ypclnt.h>
int yp_get_default_domain(
char **outdomain ); int ypbind(
char *indomain ); int 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 ypcallback incallback ); int yp_order(
char *indomain,
char *inmap,
int *outorder ); int yp_master(
char *indomain,
char *inmap,
char **outname ); char *yperr_string(
int incode ); char ypprot_err(
unsigned int incode );
DESCRIPTION
This package of functions provides an interface to the Network Informa‐
tion Service (NIS) database 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 mem‐
ory 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 multi‐
ple 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 option allows the system administrator to lock ypbind to
a particular domain and set of servers. Up to four servers can be spec‐
ified. An example of the -S option 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 cir‐
cumstances. 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() func‐
tion 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 enumera‐
tion. 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 unsuc‐
cessfully), 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 as follows:
struct ypall_callback *incallback {
int (*foreach)();
char *data; };
The foreach() function is defined as follows: foreach(
int instatus,
char *inkey,
int intkeylen,
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-termi‐
nated 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 pack‐
age 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 fore‐
ach() 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 success‐
ful, 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.
SEE ALSO
Commands: ypserv(8)
Files: ypfiles(4)ypclnt(3)
