YPCLNT(3NSL) Networking Services Library Functions YPCLNT(3NSL)


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 - NIS
Version 2 client interface

SYNOPSIS


cc [ -flag... ] file... -lnsl [ library...]
#include <rpcsvc/ypclnt.h>
#include <rpcsvc/yp_prot.h>


int yp_bind(char *indomain);


void yp_unbind (char *indomain);


int yp_get_default_domain(char **outdomain);


int yp_match(char *indomain, char *inmap, char *inkey, int inkeylen,
char *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, unsigned long *outorder);


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


char *yperr_string(int incode);


int ypprot_err(char *domain);


DESCRIPTION


This package of functions provides an interface to NIS, Network
Information Service Version 2, formerly referred to as YP. For commands
used to access NIS from a client machine, see ypbind(1M), ypwhich(1),
ypmatch(1), and ypcat(1). The package can be loaded from the standard
library, /usr/lib/libnsl.so.1.


All input parameter 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(3C) and can be freed by the user code if it 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. The indomain and inmap strings must be non-null and null-
terminated. String parameters that are accompanied by a count parameter
may not be null, but they 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.
Otherwise, they return a failure code (YPERR_xxxx). Failure codes are
described in the ERRORS section.

Routines


yp_bind()
To use the NIS name services, the client
process must be "bound" to an NIS server that
serves the appropriate domain using yp_bind().
Binding need not be done explicitly by user
code. Binding is done automatically whenever
an NIS lookup function is called. The
yp_bind() function can be called directly for
processes that make use of a backup strategy ,
for example, a local file in cases when NIS
services are not available. A process should
call yp_unbind() when it is finished using NIS
in order to free up resources.


yp_unbind()
Each binding allocates or 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. The yp_unbind() function is
available at the client interface for
processes that explicitly manage their socket
descriptors while accessing multiple domains.
The call to yp_unbind() makes the domain
unbound, and frees 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 a few more times or until the
operation succeeds, provided that rpcbind(1M)
and ypbind(1M) are running, and either:

o The client process cannot bind a
server for the proper domain; or

o RPC requests to the server fail.


Under the following circumstances, the ypclnt
layer will return control to the user code,
with either an error or success code and the
results:

o If an error is not RPC-related.

o If rpcbind is not running.

o If ypbind is not running.

o If a bound ypserv process returns
any answer (success or failure).


yp_get_default_domain()
NIS lookup calls require a map name and a
domain name, at minimum. The client process
should know the name of the map of interest.
Client processes fetch the node's default
domain by calling yp_get_default_domain() and
use the returned outdomain as the indomain
parameter to successive NIS name service
calls. The domain returned is the same as that
returned using the SI_SRPC_DOMAIN command to
the sysinfo(2) system call. The value returned
in outdomain should not be freed.


yp_match()
The yp_match() function returns the value
associated with a passed key. This key must
be exact because no pattern matching is
available. yp_match() requires a full YP map
name, such as hosts.byname, instead of the
nickname hosts.


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


yp_next()
The yp_next() function returns the next key-
value pair in a named map. The inkey
parameter must 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). Similarly, the inkeylen
parameter must be the outkeylen returned from
the earlier yp_first() or yp_next() call.

The concept of first and next is particular to
the structure of the NIS map being processed.
Retrieval order is not related to either the
lexical order within any original (non-NIS
name service) data base, or to any obvious
numerical sorting order on the keys, values,
or key-value pairs. The only ordering
guarantee 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 is seen exactly once.
Further, if the same sequence of operations is
performed on the same map at the same server,
the entries are seen in the same order.

Under conditions of heavy server load or
server failure, the domain can become unbound,
then bound once again (perhaps to a different
server) while a client is running. This
binding 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. For a better
solution to enumerating all entries in a map,
see yp_all().


yp_all()
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 takes place as a single RPC
request and response. The yp_all() function
can be used just like any other NIS name
service 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. The call to
yp_all() returns only when the transaction is
completed (successfully or unsuccessfully), or
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(int instatus, char *inkey,
int inkeylen, char *inval,
int invallen, char *indata);

The instatus parameter holds one of the return
status values defined in <rpcsvc/yp_prot.h>,
either YP_TRUE or an error code. See
ypprot_err(), for a function that converts an
NIS name service 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. The
foreach() function must 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 would 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 can
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. The foreach()
function is Boolean. It should return 0 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()
The yp_order() function returns the order
number for a map.


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


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


ypprot_err()
The ypprot_err() function takes an NIS name
service protocol error code as input, and
returns a ypclnt() layer error code, which can
be used as an input to yperr_string().


RETURN VALUES


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

YPERR_ACCESS
Access violation.


YPERR_BADARGS
The arguments to the function are bad.


YPERR_BADDB
The YP database is bad.


YPERR_BUSY
The database is busy.


YPERR_DOMAIN
Cannot bind to server on this domain.


YPERR_KEY
No such key in map.


YPERR_MAP
No such map in server's domain.


YPERR_NODOM
Local domain name not set.


YPERR_NOMORE
No more records in map database.


YPERR_PMAP
Cannot communicate with rpcbind.


YPERR_RESRC
Resource allocation failure.


YPERR_RPC
RPC failure; domain has been unbound.


YPERR_YPBIND
Cannot communicate with ypbind.


YPERR_YPERR
Internal YP server or client error.


YPERR_YPSERV
Cannot communicate with ypserv.


YPERR_VERS
YP version mismatch.


FILES


/usr/lib/libnsl.so.1

ATTRIBUTES


See attributes(5) for descriptions of the following attributes:


+---------------+-----------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-----------------+
|MT-Level | Safe |
+---------------+-----------------+

SEE ALSO


ypcat(1), ypmatch(1), ypwhich(1), rpcbind(1M), ypbind(1M), ypserv(1M),
sysinfo(2), malloc(3C), ypfiles(4), attributes(5)


February 25, 2017 YPCLNT(3NSL)