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(8),
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(8) and
ypbind(8) 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.1ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+---------------+-----------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-----------------+
|MT-Level | Safe |
+---------------+-----------------+
SEE ALSO
ypcat(1),
ypmatch(1),
ypwhich(1),
sysinfo(2),
malloc(3C),
ypfiles(5),
attributes(7),
rpcbind(8),
ypbind(8),
ypserv(8) February 17, 2023
YPCLNT(3NSL)