Technical Reference: Communications, Volume 1

nis_lookup (NIS+ API)

Purpose

Used to resolve an NIS+ name and return a copy of that object from an NIS+ server.

Syntax

cc [ flag . . . ] file. . . -lnsl [ library. . . ]

#include <rpcsvc/nis.h>

nis_result * nis_lookup(nis_name name, u_long flags);

void nis_freeresult(nis_result * result);

One of a group of NIS+ APIs that is used to locate and manipulate all NIS+ objects except the NIS+ entry objects, nis_lookup( ) resolves an NIS+ name and returns a copy of that object from an NIS+ server.

This function should be used only with names that refer to an NIS+Directory, NIS+Table, NIS+Group, or NIS+Private object. If a name refers to an NIS+ entry object, the functions listed in nis_subr(3N) should be used.

nis_lookup returns a pointer to a nis_result structure that must be freed by calling nis_freeresult( ) when you have finished using it. If one or more of the objects returned in the structure need to be retained, they can be copied with nis_clone_object(3N).

nis_lookup( ) takes two parameters, the name of the object to be resolved in name, and a flags parameter, flags. The object name is expected to correspond to the syntax of a non-indexed NIS+ name. The nis_lookup( ) function is the only function from this group that can use a non-fully qualified name. If the parameter name is not a fully qualified name, then the flag EXPAND_NAME must be specified in the call. If this flag is not specified, the function will fail with the error NIS+BADNAME.

The flags parameter is constructed by logically OR ing zero or more flags from the following list:

EXPAND_NAME: When specified, the client library will attempt to expand a partially qualified name by calling the function nis_getnames( ), which uses the environment variable nis_path.
FOLLOW_LINKS: When specified, the client library will "follow" links by issuing another NIS+ lookup call for the object named by the link. If the linked object is itself a link, then this process will iterate until either an object is found that is not a link type object, or the library has followed 16 links.
HARD_LOOKUP: When specified, the client library will retry the lookup until it is answered by a server. Using this flag will cause the library to block until at least one NIS+ server is available. If the network connectivity is impaired, this can be a relatively long time.
MASTER_ONLY: When specified, the client library will bypass any object caches and any domain replicas and fetch the object from the NIS+ master server for the object's domain. This insures that the object returned is up-to-date at the cost of a possible performance degradation and failure if the master server is unavailable or physically distant.
NO_CACHE: When specified, the client library will bypass any object caches and will get the object from either the master NIS+ server or one of its replicas.

The status value may be translated to ascii text using the function nis_sperrno( ).

On return, the objects array in the result will contain one and possibly several objects that were resolved by the request. If the FOLLOW_LINKS flag was present, on success the function could return several entry objects if the link in question pointed within a table. If an error occurred when following a link, the objects array will contain a copy of the link object itself.

Return Values

These functions return a pointer to a structure of type nis_result:

struct nis_result {
           nis_error status;
           struct {
                      u_int objects_len;
                      nis_object * objects_val;
           } objects;
           netobj     cookie;
           u_long     zticks;
           u_long     dticks;
           u_long     aticks;
           u_long     cticks;
     };

The status member contains the error status of the the operation. A text message that describes the error can be obtained by calling the function nis_sperrno( ).

The objects structure contains two members: objects_val is an array of nis_object structures; objects_lenis the number of cells in the array. These objects will be freed by a call to nis_freeresult( ). If you need to keep a copy of one or more objects, they can be copied with the function nis_clone_object( ) and freed with the function nis_destroy_object( ).

The various ticks contain details of where the time (in microseconds) was taken during a request. They can be used to tune one's data organization for faster access and to compare different database implementations.

zticks: The time spent in the NIS+ service itself, this count starts when the server receives the request and stops when it sends the reply.
dticks: The time spent in the database backend, this time is measured from the time a database call starts, until a result is returned. If the request results in multiple calls to the database, this is the sum of all the time spent in those calls.
aticks: The time spent in any accelerators or caches. This includes the time required to locate the server needed to resolve the request.
cticks: The total time spent in the request, this clock starts when you enter the client library and stops when a result is returned. By subtracting the sum of the other ticks values from this value you can obtain the local overhead of generating an NIS+ request.

Subtracting the value in dticks from the value in zticks will yield the time spent in the service code itself. Subtracting the sum of the values in zticks and aticks from the value in cticks will yield the time spent in the client library itself.

Note: All of the tick times are measured in microseconds.

Errors

The client library can return a variety of error returns and diagnostics. Following are some of the more pertinent ones:

NIS_BADNAME: The name passed to the function is not a legal NIS+ name.
NIS_CACHEEXPIRED: The object returned came from an object cache that has expired. This means that the time to live value has gone to zero and the entry may have changed. If the flag NO_CACHE was passed to the lookup function, the lookup function will retry the operation to get an unexpired copy of the object.
NIS_FOREIGNNS: The name could not be completely resolved. When the name passed to the function would resolve in a namespace that is outside the NIS+ name tree, this error is returned with a NIS+ object of type DIRECTORY. The returned object contains the type of namespace and contact information for a server within that namespace.
NIS_INVALIDOBJ: The object pointed to by obj is not a valid NIS+ object.
NIS_LINKNAMEERROR: The name passed resolved to a LINK type object and the contents of the object pointed to an invalid name.
NIS_MODFAIL: The attempted modification failed.
NIS_NAMEEXISTS: An attempt was made to add a name that already exists. To add the name, first remove the existing name and then add the new name or modify the existing named object.
NIS_NAMEUNREACHABLE: A server for the directory of the named object could not be reached. This can occur when there is a network partition or all the server s have crashed. Attempting the operation again may succeed. See the HARD_LOOKUP flag.
NIS_NOMEMORY: Generally a fatal result. It means that the service ran out of heap space.
NIS_NOSUCHNAME: This hard error indicates that the named directory of the table object does not exist. This occurs when the server that should be the parent of the server that serves the table does not know about the directory in which the table resides.
NIS_NOSUCHTABLE: The named table does not exist.
NIS_NOT_ME: A request was made to a server that does not serve the given name. Normally this will not occur; however, if you are not using the built-in location mechanism for servers, you may see this if your mechanism is broken.
NIS_NOTFOUND: The named object does not exist in the namespace.
NIS_NOTMASTER: An attempt was made to update the database on a replica server.
NIS_NOTSAMEOBJ: An attempt to remove an object from the namespace was aborted because the object that would have been removed was not the same object that was passed in the request.
NIS_RPCERROR: This fatal error indicates the RPC subsystem failed in some way. Generally there will be a syslog(3) message indicating why the RPC request failed.
NIS_S_SUCCESS: The request was successful; however, the object returned came from an object cache and not directly from the server. If you want to see objects from object caches, you must specify the flag NO_CACHE when you call the lookup function.
NIS_SUCCESS: The request was successful.
NIS_SYSTEMERROR: A generic system error occurred while attempting the request. Most commonly the server has crashed or the database has become corrupted. Check the syslog record for error messages from the server.
NIS_TRYAGAIN: The server connected to was too busy to handle your request. For the add, remove, and modify operations this is returned when either the master server for a directory is unavailable or it is in the process of checkpointing its database. It can also be returned when the server is updating its internal state or, in the case of nis_list( ), if the client specifies a callback and the server does not have the resources to handle callbacks.
NIS_UNKNOWNOBJ: The object returned is of an unknown type.

Environment

NIS_PATH: If the flag EXPAND_NAME is set, this variable is the search path used by nis_lookup( ).

Related Information

nis_add_entry, nis_first_entry, nis_list, nis_local_directory, nis_modify_entry, nis_next_entry, nis_perror, nis_remove_entry, and nis_sperror.

Network Information Services+ and NIS+ Namespace and Structure in AIX 5L Version 5.1 Network Information Services (NIS and NIS+) Guide.

TCP/IP Protocols in AIX 5L Version 5.1 System Management Guide: Communications and Networks.

List of NIS and NIS+ Programming References and Remote Procedure Call (RPC) Overview for Programming in AIX 5L Version 5.1 Communications Programming Concepts.