nis_list (NIS+ API)

Communications Technical Reference, Volume 1

nis_list (NIS+ API)

Purpose

Used to search a table in the NIS+ namespace.

Syntax

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

#include <rpcsvc/nis.h>

nis_result * nis_list(name, flags, callback userdata);

nis_name  name;

u_long  flags;

int  (*callback)( );

void  userdata;

Description

One of a group of NIS+ APIs that is used to search and modify NIS+ tables, nis_list( ) is used to search a table in the NIS+ namespace..

Entries within a table are named by NIS+ indexed names. An indexed name is a compound name that is composed of a search criteria and a simple NIS+ name that identifies a table object. A search criteria is a series of column names and their associated values enclosed in bracket [ ] characters. Indexed names have the following form:

[ colname=value,...],tablename

The list function, nis_list( ), takes an indexed name as the value for the name parameter. Here, the tablename should be a fully qualified NIS+ name unless the EXPAND_NAME flag is set. The second parameter, flags, defines how the function will respond to various conditions. The value for this parameter is created by logically OR ing together one or more flags from the following list:

FOLLOW_LINKS: If the table specified in name resolves to be a LINK type object, this flag specifies that the client library follow that link and do the search at that object. If this flag is not set and the name resolves to a link, the error NIS_NOTSEARCHABLE will be returned.
FOLLOW_PATH: This flag specifies that if the entry is not found within this table, the list operation should follow the path specified in the table object. When used in conjunction with the ALL_RESULTS flag, it specifies that the path should be followed regardless of the result of the search. When used in conjunction with the FOLLOW_LINKS flag, named tables in the path that resolve to links will be followed until the table they point to is located. If a table in the path is not reachable because no server that serves it is available, the result of the operation will be either a "soft" success or a "soft" failure to indicate that not all tables in the path could be searched. If a name in the path names is either an invalid or non-existent object, then it is silently ignored.
HARD_LOOKUP
: This flag specifies that the operation should continue trying to contact a server of the named table until a definitive result is returned (such as NIS_NOTFOUND).
Warning: Use the flag HARD_LOOKUP carefully since it can cause the application to block indefinitely during a network partition.
ALL_RESULTS: This flag can only be used in conjunction with FOLLOW_PATH and a callback function. When specified, it forces all of the tables in the path to be searched. If name does not specify a search criteria (imply that all entries are to be returned), then this flag will cause all of the entries in all of the tables in the path to be returned.
NO_CACHE: This flag specifies that the client library should bypass any client object caches and get its information directly from either the master server or a replica server for the named table.
MASTER_ONLY: This flag is even stronger than NO_CACHE as it specifies that the client library should only get its information from the master server for a particular table. This guarantees that the information will be up-to-date. However, there may be severe performance penalties associated with contacting the master server directly on large networks. When used in conjunction with the HARD_LOOKUP flag, this will block the list operation until the master server is up and available.
EXPAND_NAME: When specified, the client library will attempt to expand a partially qualified name by calling nis_getnames( ), which uses the environment variable NIS_PATH.
RETURN_RESULT: This flag is used to specify that a copy of the returning object be returned in the nis_result structure if the operation was successful.

The third parameter to nis_list( ), callback, is an optional pointer to a function that will process the ENTRY type objects that are returned from the search. If this pointer is NULL, then all entries that match the search criteria are returned in the nis_result structure; otherwise, this function will be called once for each entry returned. When called, this function should return 0 when additional objects are desired, and 1 when it no longer wishes to see any more objects.

The fourth parameter, userdata, is simply passed to callback function along with the returned entry object. The client can use this pointer to pass state information or other relevant data that the callback function might need to process the entries.

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_len is 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 anNIS+ 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_BADATTRIBUTE: The name of an attribute did not match up with a named column in the table, or the attribute did not have an associated value.
NIS_BADNAME: The name passed to the function is not a legal NIS+ name.
NIS_BADREQUEST: A problem was detected in the request structure passed to the client library.
NIS_CACHEEXPIRED: The entry 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_CBERROR: An RPC error occurred on the server while it was calling back to the client. The transaction was aborted at that time and any unsent data was discarded.
NIS_CBRESULTS: Even though the request was successful, all of the entries have been sent to your callback function and are thus not included in this result.
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 object is not a valid NIS+ entry object for the given table. This could occur if it had a mismatched number of columns, or a different data type (for example, binary or text) than the associated column in the table.
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: This soft error indicates that a server for the desired directory of the named table object could not be reached. This can occur when there is a network partition or the server has crashed. Attempting the operation again may succeed. See the HARD_LOOKUP flag.
NIS_NOCALLBACK: The server was unable to contact the callback service on your machine. This results in no data being returned.
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: No entries in the table matched the search criteria. If the search criteria was null (return all entries), then this result means that the table is empty and may safely be removed by calling the nis_remove( ). If the FOLLOW_PATH flag was set, this error indicates that none of the tables in the path contain entries that match the search criteria.
NIS_NOTMASTER: A change request was made to a server that serves the name, but it is not the master server. This can occur when a directory object changes and it specifies a new master server. Clients that have cached copies of the directory object in the /var/nis/NIS_SHARED_DIRCACHE file will need to have their cache managers restarted (use nis_cachemgr -i to flush this cache).
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_NOTSEARCHABLE: The table name resolved to a NIS+ object that was not searchable.
NIS_PARTIAL: This result is similar to NIS_NOTFOUND except that it means the request succeeded but resolved to zero entries. When this occurs, the server returns a copy of the table object instead of an entry so that the client may then process the path or implement some other local policy.
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_NOTFOUND: The named entry does not exist in the table; however, not all tables in the path could be searched, so the entry may exist in one of those tables.
NIS_S_SUCCESS: Even though the request was successful, a table in the search path was not able to be searched, so the result may not be the same as the one you would have received if that table had been accessible.
NIS_SUCCESS: The request was successful.
NIS_SYSTEMERROR: Some form of generic system error occurred while attempting the request. Check the syslog(3) record for error messages from the server.
NIS_TOOMANYATTRS: The search criteria passed to the server had more attributes than the table had searchable columns.
NIS_TRYAGAIN: The server connected to was too busy to handle your request. add_entry( ), remove_entry( ), and modify_entry( ) return this error when the master server is currently updating its internal state. It can be returned to nis_list( ) when the function specifies a callback and the server does not have the resources to handle callbacks.
NIS_TYPEMISMATCH: An attempt was made to add or modify an entry in a table, and the entry passed was of a different type than the table.

Environment

NIS_PATH: When set, this variable is the search path used by nis_list( ) if the flag EXPAND_NAME is set.

Notes:

The path used when the flag FOLLOW_PATH is specified is the one present in the first table searched. The path values in tables that are subsequently searched are ignored.
It is legal to call functions that would access the nameservice from within a list callback. However, calling a function that would itself use a callback, or calling nis_list( ) with a callback from within a list callback function, is not currently supported.

Related Information

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

Network Information Services+ and NIS+ Namespace and Structure in AIX Version 4.3 Network Information Services (NIS and NIS+) Guide.

TCP/IP Protocols in AIX Version 4.3 System Management Guide: Communications and Networks.

List of NIS and NIS+ Programming References and Remote Procedure Call (RPC) Overview for Programming in AIX Version 4.3 Communications Programming Concepts.