Method and System for Networking Computers Having Varying File Architectures

This invention relates to the field of networked computer systems and specifically to a method and means for networking a variety of computer systems, regardless of local operating systems and file structures.

Computer networks have been developed to allow files to be shared among a number of remote users or clients. In the past, computer networks were designed to support single computer types with a limited range of file systems. In prior systems, a dedicated file server is required for each type of computer. Recently, several types of computer systems have appeared on the market, each of which have file systems which are not compatible with other systems. As many alternate computer systems now coexist in many office environments, it is highly desirable to provide a method and means for allowing these systems to share files over a computer network.

One approach to networking diverse computer systems is to provide discrete file servers for each type of computer in the system. The discrete file servers may then be coupled through a device which translates the network protocol of one network into the protocol of another network. This approach requires detailed knowledge of the protocols of both networks. In addition, since file requests are routed through two separate file servers, system performance is reduced.

Another approach to networking diverse computer systems is to provide a single file server and a protocol-to-protocol converter for each foreign client in the system. For example, one common network manufactured by Novell, employs a feature referred to as a "Service Protocol Gateway," or SPG, as part of the overall architecture. The SPG translates the file server protocol of a remote user or client system to the file server protocol of the native file server. This approach has a considerable performance degradation since it also requires that the native protocol be processed. In other words, this approach requires placing a gateway between an existing file server and a foreign client or file server. The gateway performs a translation between the file server protocols of the respective systems. Unfortunately, this method often requires modification of the file servers involved, especially if any significant level of integration is to be achieved.

Still another approach to networking computers involves teaching a file server about an alternate file system by adding knowledge about a particular file server protocol to an existing file server. For example, an IBMPC can be accessed by clients of an Apple LocalTalk network if the IBM-PC is running Apple's network protocol (LocalTalk) and Apple server software (AppleShare). Unfortunately, this method offers no integration of network services. For example, this method allows integration of a foreign client into an existing network but does not allow the foreign client any access to its own user interface or network resources. The foreign client is forced to use the environment of the network it is joining.

The present invention overcomes the above problems by providing a method and means for integration of multiple networks with varying file systems while allowing each client to retain its own native environment in a manner which is totally transparent to users. The present invention also allows many foreign server types to coexist on a single integrated file server while eliminating server-to-server translations, thus improving performance. In addition, the present invention allows a central server to perform network management functions on foreign servers as well as allowing foreign file servers to be added to the system without modifying the central file server.

In summary, the present invention comprises a method and means for networking any type of computer system regardless of the local operating systems and file structures. In other words, the present invention allows multiple client types to access the file system of a central file server. In operation, a foreign file server provides file services to clients which are not recognized by a central file server. The file service requests of clients of a foreign server are directly translated into file service requests in a format recognized by the native file system of the central server without routing the file service requests through the central server. For each file service request, the central server is advised of activities of foreign file servers through a communications mechanism implemented in a series of APIs. The APIs are used to advise the central server of foreign server activities, and are not used to request file services. File services, such as opening and closing files, setinfo and getinfo are performed directly by a file system driver resident in the foreign file server.

Accordingly, it is an object of the present invention to provide a method and means for networking computers having varying file architectures.

It is another object of the present invention to allow multiple file servers to share file resources regardless of the file structures used therewith.

It is another object of the present invention to provide a method and means for providing a networked computer system wherein foreign file servers may be added to the system without modifying the central server.

It is yet another object of the present invention to allow a central server to service multiple client types.

It is still another object of the present invention to improve the speed and performance in a networked computer system having a number of diverse client types and file systems.

It is another object of the present invention to provide a method and system to allow a single file server to support a plurality of logical server types.

These and other objects may be fully appreciated through the description below and the accompanying drawings in which:

FIG. 1A is a diagram showing the improved distributed processing system of the present invention.

FIG. 1B is a diagram showing the central server table structure used to record activities of foreign file servers.

FIGS. 2A to 2C are flow diagrams detailing the operation of the I.sub.-- NetServerRegister API.

FIGS. 3A and 3B are flow diagrams of the I.sub.-- NetServerDeregister API.

FIGS. 4A and 4B are flow diagrams of the I.sub.-- NetSessionEntryMake API.

FIGS. 5A and 5B are flow diagrams of the I.sub.-- NetSessionEntryClear API, which is invoked to terminate a session entry in a data structure in a foreign server and to notify the central file server that a session has been terminated.

FIGS. 6A to 6C are flow diagrams detailing the operation of the NetSessionEntrySetInfo API, which is invoked to set information about a session.

FIGS. 7A and 7B are flow diagrams detailing the operation of the NetSessionEntryGetInfo API, which is invoked to get information about a session.

FIGS. 8A and 8D are flow diagrams of the NetConnectionEntryMake API, which is invoked to initialize a new connection entry in a data structure in the foreign server and to notify the central server that a new connection has been created.

FIGS. 9A and 9B are flow diagrams of the NetConnectionEntryClear API, which is invoked to terminate a connection entry in a data structure in a foreign server and to notify the central file server that a connection has been terminated.

FIGS. 10A to 10C are flow diagrams detailing the operation of the I.sub.-- NetConnectionEntrySetInfo API of the present invention.

FIGS. 11A and 11B are flow diagrams of the I.sub.-- NetConnectionEntryGetInfo API of the present invention.

FIGS. 12A to 12C are flow diagrams of the I.sub.-- NetFileEntryMake API of the present invention.

FIGS. 13A and 13B are flow diagrams of the I.sub.-- NetFileEntryClear API of the present invention.

FIGS. 14A to 14C are flow diagrams of the I.sub.-- NetFileEntrySetInfo API of the present invention.

FIGS. 15A to 15B are flow diagrams of the I.sub.-- NetFileEntryGetInfo API of the present invention.

FIG. 16 is a flow diagram of the clear/save function called by various APIs of the present invention.

FIG. 17 is a flow diagram of the allocate function called by various APIs of the present invention.

Referring now to FIG. 1A, a diagram of the improved distributed computer system of the present invention is shown. The present invention is adapted to allow the files resident in a central server to be accessed and modified by not only central file server clients, but by clients of foreign file servers as well. In addition, the present invention provides a method and means for integrating any number of file servers, regardless of the operating system and file structures used with each server. The system 100 comprises a central file server 102, which is coupled to a file system 104. The central file server 102 and file system 104 are adapted to provide file services to a plurality of clients 106, 108. Clients are coupled to the file server 102 through local area network (LAN) communication lines 110. In the preferred practice of the present invention, clients request file services from the central server 102 by sending requests in the form of server message blocks (SMBs) in accordance with the SMB protocol developed by Microsoft, IBM and Intel. Similarly, the central file server 102 responds to file service request SMBs with SMBs which mirror the request SMBs and which may contain the file data requested by a client. The SMB network protocol is described in a document entitled Microsoft Networks/Open Net File Sharing Protocol V 1.9, 1987, available from Microsoft Corporation, One Microsoft Way, Redmond, Wash. While the system 100 is shown with two clients coupled to central file server 102, those skilled in the art will readily appreciate that virtually any number of clients could be coupled to the central file server 102. While the present invention is illustrated as employing a central server which is adapted for use with the SMB protocol, those skilled in the art will appreciate that the principles of the present invention may be used with virtually any network protocol.

In its simplest form, the central server 102 may be thought of as comprising a transport 112, a system kernel 114 and a server module 116. The transport 112 interfaces the network communication lines 110 to the kernel 114 and server module 116. The transport 112 moves data on to or off of network communication lines 110. As in other systems, the kernel 114 is responsible for communicating with the file system 104 and processing file service requests. The server module 116 receives and interprets network file requests and communicates them to kernel 114. The server module 116 also formats and assembles network response messages. For example, in operation, a client may wish to open a file. The client transmits an open file SMB to the central server 102 where it is intercepted by transport 112. The, transport 112 routes the open file SMB to server module 116. The server module then unpacks the SMB request and converts it to a conventional operating system file request, such as DosOpen, in the well-known OS/2 operating system. The file system request is then routed to the file system 104 through kernel 114. Once the requested file operation is completed, the kernel 114 routes the requested data (which includes a file handle in the case of a DosOpen) to the server module which packages the requested data in the form of a response SMB. The response SMB is then routed to the requesting client through the transport 112.

The present invention is also adapted to support file service requests from foreign file servers for files which are resident on the central file server 102. While the system 100 is illustrated with a single foreign server 118, the present invention contemplates the use of numerous foreign file servers, and there is virtually no limit to the number of foreign servers which could be supported in accordance with the techniques of the present invention. While the foreign server 118 may be implemented as an independent system, it is contemplated that the foreign server 118 may be integrated with the central file server 102 and the servers 102, 118 wherein the entire system may be implemented within a single process 120 and resident on a single computer system. In its simplest form, the server 118 may be thought of as comprising a transport 122, a kernel 124 and a server module 126, whose functions are identical to transport 112, kernel 114 and server module 116, respectively. It is contemplated that the foreign server 118 may maintain its own file system 128 or share file system 104 and support its own client base as indicated by clients 132, 134 and 136. While in the system 100, the central server 102 may be adapted to service clients operating under the MS-DOS or OS/2 operating systems and using file systems compatible therewith, the foreign file server 118 may be adapted to service clients using a completely different operating system and file system, such as the operating system and file system used with Apple Macintosh computers. For example, the foreign server 118 may be configured to support the Apple LocalTalk and AppleShare local area network protocols.

The present invention provides an efficient method and means for the clients of the foreign file server 118 to have complete and transparent access to files maintained in file system 104. When performing foreign network operations locally, assuming the file server 118 were adapted for use with Macintosh type clients, a client would generate a network file request in the form of an Apple Filing Protocol request (AFP). The Apple Filing Protocol is well known. As with the central file server 112, the request AFP is routed to the server module 126, which disassembles the request AFP and routes the file system request to kernel 124. Kernel 124 then instructs the file system 128 to perform the requested file operation. Once the file operation has been performed, the requested data is routed through the kernel 124 and server module 126 to generate a response AFP. The response AFP is then sent to the requesting client through transport 122.

According to the principles of the present invention, in addition to performing foreign operations locally, the foreign server 118 is adapted to perform file services with file system 104. In prior systems, if a foreign client requests file services from a network server having an incompatible file system, the file service request is routed to the server module of the incompatible system where it is translated into a form which is recognized by its associated kernel. The kernel then translates the file system request into a form which is recognized by the incompatible file system. Therefore, file service requests go through two levels of translation when processing file service requests from foreign file servers. The present invention provides a novel method and means for facilitating file service requests from foreign servers by providing a server module 126 which includes a mapping means 140, which directly converts file service requests from foreign clients 132 to 136 into a form which is recognized by file system 104.

While the present invention provides a novel architecture for distributed computer systems in which the mapping means 140 is only one component, mapping means are a well-known means for converting file protocols. One example of a known mapping means is the LAN MANAGER NETWARE Server (LMNS) available from Racal-Interlan, which converts Novell Netware file system requests into Microsoft LANManager and OS/2 requests.

The translated file service request is directly communicated to file system 104 through channel 142, thus eliminating the second level of translation required if the file service request is routed through server module 116. In addition, the present invention contemplates the use of channel 144 to facilitate communication between central server module 116 and foreign server module 126, so that file system functions are provided in a coordinated manner wherein the central server 102 is fully apprised of the actions of foreign server 118.

For example, the present invention is particularly adapted for use in a multiuser/multitasking environment. In this type of system, files must be protected from multiple users attempting to modify the file simultaneously. If files are not protected from multiple user modification, users may be working with inconsistent versions of the same file. Therefore, in a multiple user environment, files are temporarily locked when modifications are made by a single user and unlocked when the modification is complete. In accordance with the principles of the present invention, the foreign server 118 may access the file system 104 directly. Therefore, the central server must be informed which files are opened and locked by foreign server 118. One advantage of the present invention is that the central server can record and display statistics for file operations for the entire system 100.

While files of the file system 104 are being processed by foreign server module 126, the foreign server module 126 calls a number of application program interfaces (APIs) to instruct the central server module 116 as to file service functions being directly performed on the file system 104. An API may be thought of as a modular unit which performs a known function or procedure. APIs typically employ data structures wherein certain values may be accessed, set and manipulated, and certain values and/or error codes are often returned by APIs. The central server 116 then responds to server APIs with entry points to dynamic linked library (DLL) APIs to confirm communication between the respective file servers. DLLs are a well-known feature of the OS/2 operating system and are specific instances of APIs which are available as common resources to any application or other type of executable code. Therefore, system performance is greatly enhanced by allowing direct file system access from foreign file servers to the central file system 104, and by reducing communication between the central file server and foreign servers to information about the status of files.

While the kernel and server module of the central server are preferably implemented for use with the OS/2 operating system developed by Microsoft, those skilled in the art will appreciate that the present invention may be implemented with virtually any operating system or combination of operating systems. The present invention is adapted for use with a number of foreign file servers, as indicated by foreign file servers 146 to 152.

In accordance with the teachings of the present invention, the activities of foreign servers are tracked on the central server in the form of tables or internal data structures of the type shown in FIG. 1B. On a high level, the central server maintains a repository, or table 160, which stores information for each foreign server active in the system. Each instance 162 of foreign server entries in table 160 includes a reference 164 to four tables 166 to 172. Table 166 maintains information for each session and contains one entry 167 for each session. Table 168 contains one entry 169 for each connection. Table 170 contains one entry 171 for each file, and table 172 contains one entry 173 for each client type supported by the foreign server. The concept of sessions, connections, files and client types is further discussed below.

The data structure for table entry 162 is set forth below:

The APIS of the present invention may be divided into four basic classifications: initialization and termination of communications channels, session operations connection operations, and file operations. In addition, the present invention may employ existing APIs, such as APIs used for resource allocation and sharing, and message operations. Initialization and termination APIs are used to establish communications channels between the central server and foreign file servers. Session APIs notify the central server of session operations, such as the addition or deletion of sessions, setting session information and getting session information. Connection APIs notify the central server of attempts to access a shared resource by a client. A connection may be thought of as a particular instance of a client access to a shared resource. Operations which may be performed on a connection by a client include connection establishment, termination, setting of file status and retrieval of file status. File APIs notify the central server of file operations performed by clients through a foreign server. Such operations can include operations such as file open and file close.

The overall operation of the present invention may be explained as follows. Upon foreign server start-up, the foreign server calls the I.sub.-- NetServerRegister API to register its services with the central server. In the register.sub.-- info.sub.-- 0 data structure passed to the central server, the foreign server specifies a DLL module which contains the APIs used by the central server to communicate with the foreign server. When a client of the foreign server wishes to connect to a central server resource, the foreign server calls the I.sub.-- NetSessionEntryMake API to establish a session from the specified client to the central server. This session is the parent of later connections and file operations. When the client of the foreign server wishes to access a central server resource, the foreign server calls the I.sub.-- NetConnectionEntryMake API to notify the central server of the request. Once a session and connection have been established on the central server, the foreign server services its client's file system requests through use of the file APIs described below. When a client of the foreign server wishes to cease access to a central server resource, the foreign server issues a call to the I.sub.-- NetConnectionEntry Clear API to notify the central server. When all connections of a specific client session have been cleared, the foreign server calls the I.sub.-- NetSessionEntryClear API to notify the central server to break the connection to the central server resource. When a foreign server wishes to cease operation, it calls the I.sub.-- NetServerDeregister API to terminate its services with the central server. For each API called by the foreign server, the central server responds with a status code either confirming the operation or indicating an error.

For operations such as central service shutdown initiated by the central server, existing OS/2 local area network APIs and APIs contained within a DLL provided by the foreign server are used to communicate the operations to the foreign server. These APIs are set forth below: ##SPC1##

It should be noted that the above APIs may be implemented in a variety of ways, which are readily apparent to persons of ordinary skill, depending on foreign server implementation.

In addition to the APIs discussed herein, the present invention is also adapted to invoke existing APIs which are currently available in the Microsoft "LanMan" local area network. A detailed technical description of the Microsoft LanMan local area network is set forth in a document "LANManager Programmers Reference." An example of an existing API used in the operation of the present invention is the NetServiceControl API used to instruct servers and clients that a network shutdown is about to occur.

The following external data structures are maintained by the central server in the course of the operation of the present invention.

All data structures and predefined values used by the following APIs have been previously defined in the LANManager Programmers Reference mentioned above.

All data structures and predefined values used by the following APIs have been previously defined in the LANManager Programmers Reference mentioned above.

The following figures of the drawings describe the operation of the present invention. FIGS. 2A to 2C are flow diagrams of the I.sub.-- NetServerRegister, which is an API used to register the foreign service with the file server of the present invention. This is the initial call made from a foreign server to the central to instruct the central server that a foreign server requires file services on the central server. Communication between the central server and the foreign server occurs in three phases:

1. An initial phase wherein the foreign server instructs the central server that its foreign services are available to the central server.

2. An intermediate phase wherein the foreign server processes foreign client requests and reports such actions to the central server.

3. A final stage wherein foreign server notifies central server that its services are no longer available.

The I.sub.-- NetServerRegister API 200 is called to perform the initial phase. This process is invoked to set up any necessary data structures within the central server. The data structures for this API are set forth below:

The central server uses these data structures for tracking which foreign servers are active and available to foreign clients. In general, the process 200 is used to validate parameters, to determine whether the network is active, to verify that the caller of the API has authority to use the API, to validate parameter values, to locate central server data in memory, to protect central server data against multiple client access, to perform a requested system function, to unprotect the central server data and to release access to central server data. If an error is detected at any point in the process, all nonrequested system functions are reversed and the appropriate error code is returned to the caller.

When invoked, the process 200 begins with item 202 which performs error checking on the parameter passed to the central server to determine whether the parameters reference is a legal location within memory. Decision 204 then determines whether the network is installed and active. If not, a NERR.sub.-- NetNotStarted error code is returned to the caller in termination block 206. If decision 204 determines the network is installed and active, control passes to decision 208, which determines whether the caller has authority to invoke the API 200. If not, a ERROR.sub.-- NETWORK.sub.-- ACCESS.sub.-- DENIED error code is returned to the caller in termination block 210. If decision 208 determines the caller has authority to proceed in the API 200, control passes to decisions 212, 216, 220, 228 and 232 to validate any parameters passed the API. Decision 212 determines whether the buffer length parameter passed to the API is correct. If not, error NERR.sub.-- BufTooSmall is returned by termination block 218. Decision 216 determines whether the data structure level of detail is zero. If not, error ERROR.sub.-- INVALID.sub.-- LEVEL is returned by termination block 218. Decision 220 determines whether the pointers stored in the buffer are pointing to valid positions in memory. If not, ERROR.sub.-- INVALID.sub.-- PARAMETER is returned by termination block 222. Decision 228 then determines whether the name of the DLL module identified in the buffer is valid. A DLL is a dynamic linked library which is a shared library resource which may be used by any executable file in the system. DLLs are used for two forms of communication:

1. Whenever the foreign server communicates with central server through APIs discussed herein; and

2. Whenever the central server communicates with foreign server, communication is provided through a DLL provided by foreign server.

In the preferred practice of the present invention, the foreign server provides a DLL to the central with known entry points, and is of the form AltSrvXXXYYY, where XXX is the object in which the API acts on and YYY is the operation to be performed on the object, e.g., file=XXX and close=YYY. This technique allows the central server to receive feedback from the foreign servers as to progress or outcome of the called entry point.

If decision 228 determines the DLL module name is not valid, ERROR.sub.-- INVALID.sub.-- PARAMETER is returned by termination block 230.

Referring now to FIG. 2B, decision 232 determines whether the provided DLL module has the correct entry points. If not, ERROR.sub.-- INVALID.sub.-- PROCNAME is returned by termination block 234. Decision 236 determines whether the caller can access the central server memory. If not, error NERR.sub.-- ServerNotStarted is returned by termination block 238. Decision 240 determines whether the data structure that contains the entries for the foreign servers can be protected so that multiple access to the data structure is prohibited. If not, e.g., if the protection mechanism fails, item 242 reverses the accessing of the server segments through an internal API call and NERR.sub.-- InternalError is returned by termination block 244. Loop 245 is invoked to set up any internal data structures, if necessary. Decision 246 determines whether a table for the foreign server entries exists. If not, item 248 allocates a server table. If while allocating a server table, the allocation attempt fails, an error is returned to the caller and all previous operations are reversed using a clear/free operation. The clear/free operation is discussed in further detail below, in conjunction with FIG. 16. The allocate operation is also discussed in further detail below, in conjunction with FIG. 17.

Once the server tables are allocated, decision 250 determines whether the foreign server is already registered, i.e., the foreign server is already known to the central server. If so, NERR.sub.-- ServiceInstalled is returned by termination block 252. Decision 254 determines whether sufficient table space is available within the central server to accommodate the registering server. If not, NERR.sub.-- TooManyServers is returned by termination block 256. Items 258-270 then perform the requested operation, such as allocating and initializing all necessary data structures. For each of the functions performed in items 258-270, if an error is encountered, or if the allocation attempt fails, an error is returned to the caller and all previous operations are reversed. Those skilled in the art will appreciate that semaphores are a form of mutual exclusion. Item 272 is invoked to release a semaphore to relinquish control of the data structure. Item 274 is invoked to release server segments by calling an internal API call.

Referring now to FIGS. 3A and 3B, the I.sub.-- NetServerDeregister API 300 notifies the central server that a foreign server is withdrawing services. This notification allows the central server to perform any necessary operations, such as disposing of any internal data structures and updating any necessary statistics, etc. The data structures used with this API are set forth below:

When invoked, the process 300 begins with decision 302, which determines whether the network is installed and active. If not, a NERR.sub.-- NetNotStarted error code is returned to the caller in termination block 304. If decision 302 determines the network is installed and active, control passes to decision 306, which determines whether the caller has authority to invoke the API 300. If not, a ERROR.sub.-- NETWORK.sub.-- ACCESS.sub.-- DENIED error code is returned to the caller in termination block 308. If decision 306 determines the caller has authority to proceed in the API 300, control passes to decision 310, which determines whether the caller can access the central server memory. If not, error NERR.sub.-- ServerNotStarted is returned by termination block 310. Decision 314 determines whether the data structure that contains the entries for the foreign servers can be protected so that multiple access to the data structure is prohibited. If not, e.g., if the protection mechanism fails, item 316 reverses the accessing of the server segments through an internal API call and NERR.sub.-- InternalError is returned by termination block 318. Decision 320 then determines whether the foreign server identification number value is within a valid range. The foreign server identification number is used to identify foreign servers for communication with the central server. If the foreign server identification number is not within the valid range, NERR.sub.-- NoSuchServer is returned by termination block 322. Items 324 to 330 are invoked to dispose of allocated data structures as well as the information contained therein. Item 332 is invoked to release a semaphore to relinquish control of the data structure. Item 334 is then invoked to release server segments by calling an internal API call.

Referring now to FIGS. 4A and 4B, the I.sub.-- NetSessionEntryMake API 400 is invoked to initialize a new session entry in a data structure in the foreign server and to notify the central server that a new session has been created. In the context of the present invention, sessions may be thought of as a link between two computers, such as a link between a specific workstation and a server, or a client and a server. A session is made up of one or more connections. Connections are a particular instance of a session. Session tables are used for tracking session-related information, such as the owner of the session, whether there are any open files in the session, the number of connections in a session, etc.

The external data structures of the I.sub.-- NetSessionEntryMake API 400 are set forth below:

When the API 400 is invoked, the process 400 begins with item 402, which performs error checking on the parameters passed to the central server, to determine whether the parameters reference is a legal location within memory. Decision 404 then determines whether the network is installed and active. If not, a NERR.sub.-- NetNotStarted error code is returned to the caller in termination block 406. If decision 404 determines the network is installed and active, control passes to decision 408, which determines whether the caller has authority to invoke the API 400. If not, a ERROR.sub.-- NETWORK.sub.-- ACCESS.sub.-- DENIED error code i s returned to the caller in termination block 410. If decision 408 determines the caller has authority to proceed in the API 400, control passes to decision 412, which determines whether the data structure level of detail is valid. If not, error ERROR.sub.-- INVALID.sub.-- LEVEL is returned by termination block 414. Decision 416 then determines whether the buffer length parameter passed to the API is correct. If not, error NERR.sub.-- BufToSmall is returned by termination block 418. Decision 420 determines whether the pointers stored in the buffer are pointing to valid positions in memory. If not, ERROR.sub.-- INVALID.sub.-- PARAMETER is returned by termination block 422. Decision 424 then determines whether the caller can access the central server memory. If not, error NERR.sub.-- ServerNotStarted is returned by termination block 426. Decision 428 determines whether the data structure that contains the entries for the foreign servers can be protected so that multiple access to the data structure is prohibited. If not, e.g., if the protection mechanism fails, item 430 reverses the accessing of the server segments through an internal API call and NERR.sub.-- InternalError is returned by termination block 432. Decision 434 then determines whether the foreign server identification number value is within a valid range. If the foreign server identification number is not within a valid range, NERR.sub.-- NoSuchServer is returned by termination block 436. Decision 438 determines whether the pointers stored in the buffer are pointing to valid positions in memory. If not, ERROR.sub.-- INVALID.sub.-- PARAMETER is returned by termination block 440. Item 442 is invoked to allocate a new entry in the new session table. In case of an error, e.g., if the allocation attempt fails, an error is returned to the caller and all previous operations are reversed. Item 448 then initializes and fills the new session table entry. Item 450 is invoked to release a semaphore to relinquish control of the data structure. Item 452 is invoked to release server segments by calling an internal API.

Referring now to FIGS. 5A and 5B, the I.sub.-- NetSessionEntryClear API 500 is invoked to terminate a session entry in a data structure in a foreign server and to notify the central file server that a session has been terminated. The data structure for this API is set forth below:

When invoked, decision 502 determines whether the network is installed and active. If not, a Nerr.sub.-- NetNotStarted error code is returned to the caller in termination block 504. If decision 502 determines the network is installed and active, control passes to decision 502, which determines whether the caller has authority to invoke the API 500. If not, a ERROR.sub.-- NETWORK.sub.-- ACCESS.sub.-- DENIED error code is returned to the caller in termination block 508. If decision 506 determines the caller has authority to proceed in the API 500, control passes to decision 510, which determines whether the foreign server identification number value is within a valid range. If the foreign server identification number is not within a valid range, NERR.sub.-- NoSuchServer is returned by termination block 511. Decision 512 then determines whether the caller can access the central server memory. If not, error NERR.sub.-- ServerNotStarted is returned by termination block 514.

Decision 516 determines whether the data structure that contains the entries for the foreign servers can be protected so that multiple access to the data structure is prohibited. If not, e.g., if the protection mechanism fails, item 518 reverses the accessing of the server segments through an internal API call and NERR.sub.-- InternalError is returned by termination block 520. Decision 522 determines whether foreign server I.D. and entry in the alternate server table is valid. If not, NERR.sub.-- NoSuchServer is returned by termination block 524. Decision 526 determines whether the session I.D. is valid. The session I.D. is used as an index to the session table. If the session I.D. is not valid, NERR.sub.-- NoSuchSession is returned by termination block 528. Loop 530, which comprises item 532 and decision 534, then disposes of all open connections and open file entries associated with the session. Item 536 is invoked to update the foreign servers statistics. Item 538 is invoked to release a semaphore to relinquish control of the data structure. Item 540 is invoked to release server segments by calling an internal API.

Referring now to FIGS. 6A to 6C, the I.sub.-- NetSessionEntrySetInfo.sub.-- API 600 is invoked to set information about a session entry. The data structure for this API is set forth below:

When invoked, the process 600 begins with item 602, which performs error checking on the parameters passed to the central server, to determine whether the parameters reference is a legal location within memory. Decision 604 then determines whether the network is installed and active. If not, a NERR.sub.-- NetNotStarted error code is returned to the caller in termination block 606. If decision 604 determines the network is installed and active, control passes to decision 608, which determines whether the caller has authority to invoke the API 600. If not, a ERROR.sub.-- NETWORK.sub.-- ACCESS.sub.-- DENIED error code is returned to the caller in termination block 610. If decision 608 determines the caller has authority to proceed with the API 600, control passes to decision 612 to determine whether the level is valid. Decision 616 then determines whether the parameter number (parmnum) is valid. If not, termination block 618 returns error ERROR.sub.-- INVALID.sub.-- PARAMETER. Decision 620 determines whether the parameter buffer length (buflen) is valid. If not, termination block 622 returns error NERR.sub.-- BufTooSmall. Decision 624 determines whether the parameter server identification code (server.sub.-- id) is valid. If not, termination block 626 returns NERR.sub.-- NoSuchServer. Decision 628 determines whether the caller can access the central server memory. If not, error NERR.sub.-- ServerNotStarted is returned by termination block 630. Decision 632 determines whether the data structure that contains the entries for the foreign servers can be protected so that multiple access to the data structure is prohibited. If not, e.g., if the protection mechanism fails, item 634 reverses the accessing of the server segments through an internal API call and NERR.sub.-- InternalError is returned by termination block 636. Decision 638 determines whether the server table entry is valid. If not, termination block 640 performs a clear/free operation and returns error NERR.sub.-- NoSuchServer. Decision 642 then determines whether the session table entry is valid. If not, termination block 644 performs a clear/free operation and returns error NERR.sub.-- NoSuchServer. Otherwise, control then passes to item 646 to set the appropriate parameters in the session table entry according to the parmnum parameter. The session table entry is set with information from the parameter buffer. Item 648 is invoked to release a semaphore to relinquish control of the data structure. Item 650 is invoked to release server segments by calling an internal API.

Referring now to FIGS. 7A and 7B, the I.sub.-- NetSessionEntryGetInfo API 700 is invoked to get information about a session. This API is useful for determining the status of the session, such as how many connections are in the session, what clients are in the session, etc. The data structures for this API are set forth below:

When invoked, the process 700 begins with item 702, which performs error checking on the parameters passed to the central server, to determine whether the parameters reference is a legal location within memory. Decision 704 then determines whether the network is installed and active. If not, a NERR.sub.-- NetNotStarted error code is returned to the caller in termination block 706. If decision 704 determines the network is installed and active, control passes o decision 708, which determines whether the caller has authority to invoke the API 700. If not, a ERROR.sub.-- NETWORK.sub.-- ACCESS.sub.-- DENIED error code is returned to the caller in termination block 710. If decision 708 determines the caller has authority to proceed in the API 700, control passes to decision 712, which determines whether the data structure level of detail is valid. If not, error ERROR.sub.-- INVALID.sub.-- LEVEL is returned by termination block 714. Decision 716 determines whether the parameter server.sub.-- id is valid. If not, termination block 716 returns NERR.sub.-- NoSuchServer. Decision 720 determines whether the caller can access the central server memory. If not, error NERR.sub.-- ServerNotStarted is returned by termination block 722. Decision 724 determines whether the data structure that contains the entries for the foreign servers can be protected so that multiple access to the data structure is prohibited. If not, e.g., if the protection mechanism fails, item 726 reverses the accessing of the server segments through an internal API call and NERR.sub.-- InternalError is returned by termination block 728.

Decision 730 determines whether the server table entry is valid. If not, termination block 732 performs a clear/free operation and returns error NERR.sub.-- NoSuchServer. Decision 734 then determines whether the session table entry is valid. If not, termination block 736 performs a clear/free operation and returns error NERR.sub.-- NoSuchServer. Otherwise, control then passes to item 738 to release a semaphore to relinquish control of the data structure. Control then passes to item 740, which copies information to a parameter buffer according to a specified level. Item 742 is then invoked to release server segments by calling an internal API.

Referring now to FIGS. 8A to 8D, the I.sub.-- NetConnectionEntryMake API 800 establishes a new connection in the connection table. This API is used to inform the central server of new connections. The data structure for this API is set forth below:

When invoked, the process 800 begins with item 802, which performs error checking on the parameters passed to the central server to determine whether the parameters reference is a legal location within memory. Decision 804 then determines whether the network is installed and active. If not, a NERR.sub.-- NetNotStarted error code is returned to the caller in termination block 806. If decision 804 determines the network is installed and active, control passes to decision 808, which determines whether the caller has authority to invoke the API 800. If not, a ERROR.sub.-- NETWORK.sub.-- ACCESS.sub.-- DENIED error code is returned to the caller in termination block 810. If decision 808 determines the caller has authority to proceed in the API 800, control passes to decision 812, which determines whether the data structure level of detail is valid. If not, error ERROR.sub.-- INVALID.sub.-- LEVEL is returned by termination block 814. Decision 816 determines whether the buffer length parameter passed to the API is correct. If not, error NERR.sub.-- BufTooSmall is returned by termination block 818. Decision 820 determines whether the pointers stored in the buffer are pointing to valid positions in memory. If not, ERROR.sub.-- INVALID.sub.-- PARAMETER is returned by termination block 822. Decision 824 determines whether the caller can access the central server memory. If not, error NERR.sub.-- ServerNotStarted is returned by termination block 826. Decision 828 determines whether the data structure that contains the entries for the foreign servers can be protected so that multiple access to the data structure is prohibited. If not, e.g., if the protection mechanism fails, item 830 reverses the accessing of the server segments through an internal API call and NERR.sub.-- InternalError is returned by termination block 832. Control then passes to decision 834, which determines whether the foreign server identification number value is within a valid range. If the foreign server identification number is not within a valid range, NERR.sub.-- NoSuchServer is returned by termination block 836. Decision 838 determines whether foreign server I.D and entry in the alternate server table is valid. If not NERR.sub.-- NoSuchServer is returned by termination block 840. Decision 842 determines whether the session I.D. is valid. The session I.D. is used as an index to the session table. If the session I.D. is not valid, NERR.sub.-- NoSuchSession is returned by termination block 852. Decision 846 then determines whether the session table entry is valid. If not, termination block 848 performs a clear/free operation and returns error NERR.sub.-- NoSuchServer. Otherwise, control then passes to item Decision 850 to determine whether the data structure that contains the entries for valid network names can be protected so that multiple access to the data structure is prohibited. If not, e.g., if the protection mechanism fails, termination block 852 reverses the accessing of the server segments through an internal API call and NERR.sub.-- InternalError is returned. Decision 854 determines whether the specified connection in a central server table refers to a valid network name. If not, item 856 relinquishes control of the valid network name table by a clearing semaphore. Termination block 858 performs a clear/free operation and returns an error NERR.sub.-- NetNameNotFound. If Decision 854 determines that the specified connection in a central server table refers to a valid network name, decision 860 determines whether the number of specified connections is less than a predetermined number of connections. If so, item 862 relinquishes control of the valid network name table by a clearing semaphore. Termination block 864 performs a clear/free operation and returns NERR.sub.-- TooManyConnections. If there are not too many connections, item 866 allocates a new connection table entry. Decision 868 then determines whether the allocation failed. If so, item 870 logs the error. Item 872 then relinquishes control of the valid network name table by a clearing semaphore. Termination block 874 then performs a clear/free operation and returns an error ERROR.sub.-- NOT.sub.-- ENOUGH.sub.-- MEMORY. If the allocation does succeed, item 876 initializes the new connection table entry. Item 878 then updates the foreign server statistics and item 880 relinquishes control of the valid network name table by a clearing semaphore. Item 882 is invoked to release a semaphore to relinquish control of the data structure. Item 884 is invoked to release server segments by calling an internal API.

Referring now to FIG. 9A and 9B, flow diagrams of the I.sub.-- NetConnectionEntryClear. When invoked, decision 902 determines whether the network is installed and active. If not, a NERR.sub.-- NetNotStarted error code is returned to the caller in termination block 904. If decision 902 determines the network is installed and active, control passes to decision 906, which determines whether the caller has authority to invoke the API 900. If not, a ERROR.sub.-- NETWORK.sub.-- ACCESS.sub.-- DENIED error code is returned to the caller in termination block 908. If decision 906 determines the caller has authority to proceed in the API 200, control passes to decision 910, which determines whether the foreign server identification number value is within a valid range. If the foreign server identification number is not within a valid range, NERR.sub.-- NoSuchServer is returned by termination block 912. Decision 914 determines whether the caller can access the central server memory. If not, error NERR.sub.-- ServerNotStarted is returned by termination block 916. Decision 918 determines whether the data structure that contains the entries for the foreign servers can be protected so that multiple access to the data structure is prohibited. If not, e.g., if the protection mechanism fails, item 920 reverses the accessing of the server segments through an internal API call and NERR.sub.-- InternalError is returned by termination block 922. Decision 924 determines whether foreign server I.D and entry in the alternate server table is valid. If not, NERR.sub.-- NoSuchServer is returned by termination block 926. Decision 928 determines whether the connection I.D. parameter (conn.sub.-- id) is valid. If not, a clear/free operation is performed and error NERR.sub.-- NoSuchConnection is returned by termination block 930. If decision 928 determines the connection is valid, decision 932 checks whether the connection table entry is valid. If not, termination block 934 performs a clear/free operation and returns the error NERR.sub.-- NoSuchConnection. Decision 936 determines whether the connection has any open files. If so, item 938 disposes of all open file entries for this connection. If the connection has no open files, or when item 938 is complete, control passes to item 940, which updates the foreign server statistics. Item 942 is invoked to release a semaphore to relinquish control of the data structure. Item 944 is invoked to release server segments by calling an internal API.

Referring now to FIGS. 10A to 10C, the I.sub.-- NetConnectionEntrySetInfo API is called to set information about a connection entry and for setting the status of a connection. The data structure for this API is set forth below.

When invoked, the process 1000 begins with item 1002, performs error checking on the parameters passed to the central server, to determine whether the parameters reference is a legal location within memory. Decision 1004 then determines whether the network is installed and active. If not, a NERR.sub.-- NetNotStarted error code is returned to the caller in termination block 1006. If decision 1004 determines the network is installed and active, control passes to decision 1008, which determines whether the caller has authority to invoke the API 1000. If not, a ERROR.sub.-- NETWORK.sub.-- ACCESS.sub.-- DENIED error code is returned to the caller in termination block 1010. If decision 1008 determines the caller has authority to proceed in the API 1000, control passes to decision 1012, which determines whether the data structure level of detail is valid. If not, error ERROR.sub.-- INVALID.sub.-- LEVEL is returned by termination block 1014. Decision 1016 determines whether the parmnum parameter is valid. If not, termination block 1018 returns error ERROR.sub.-- INVALID.sub.-- PARAMETER. If the parmnum parameter is valid, decision 1020 determines whether the buffer length parameter passed to the API is correct. If not, error NERR.sub.-- BufTooSmall is returned by termination block 1022. Control then passes to decision 1024, which determines whether the foreign server identification number value is within a valid range. If the foreign server identification number is not within a valid range, NERR.sub.-- NoSuchServer is returned by termination block 1026. Decision 1028 determines whether the caller can access the central server memory. If not, error NERR.sub.-- ServerNotStarted is returned by termination block 1030. Decision 1032 determines whether the data structure that contains the entries for the foreign servers can be protected so that multiple access to the data structure is prohibited. If not, e.g., if the protection mechanism fails, item 1034 reverses the accessing of the server segments through an internal API call and NERR.sub.-- InternalError is returned by termination block 1036. Decision 1038 determines whether foreign server I.D. entry in the alternate server table is valid. If not, NERR.sub.-- NoSuchServer is returned by termination block 1040. Decision 1042 determines whether the connection I.D. parameter (conn.sub.-- id) is valid. If not, a clear/free operation is performed and error NERR.sub.-- NoSuchConnection is returned by termination block 1044. If decision 1042 determines the connection is valid, decision 1046 checks whether the connection table entry is valid. If not, termination block 1048 performs a clear/free operation and returns the error NERR.sub.-- NoSuchConnection. Item 1050 sets connection information according to parameter parmnum. The connection information includes the number of open files owned by the connection. Item 1052 is invoked to release a semaphore to relinquish control of the data structure. Item 1054 is invoked to release server segments by calling an internal API.

Referring now to FIGS. 11A and 11B, I.sub.-- NetConnectionGetInfo API 1100 is used to retrieve information about a connection and for determining the status of a connection. The data structure for this API is set forth below:

When invoked, the process 1100 begins with item 1102, which performs error checking on the parameters passed to the central server, to determine whether the parameters reference is a legal location within memory. Decision 1104 then determines whether the network is installed and active. If not, a NERR.sub.-- NetNotStarted error code is returned to the caller in termination block 1106. If decision 1104 determines the network is installed and active, control passes to decision 1108 which determines whether the caller has authority to invoke the API 1100. If not, a ERROR.sub.-- NETWORK.sub.-- ACCESS.sub.-- DENIED error code is returned to the caller in termination block 1110. If decision 1108 determines the caller has authority to proceed in the API 200, control passes to decision 1112, which determines whether the data structure level of detail is zero. If not, error ERROR.sub.-- INVALID.sub.-- LEVEL is returned by termination block 1114. Decision 1116 determines whether the parameter server.sub.-- id (server identification code) is valid. If not, termination block 118 returns NERR.sub.-- NoSuchServer. Decision 1120 determines whether the caller can access the central server memory. If not, error NERR.sub.-- ServerNotStarted is returned by termination block 1122. Decision 1124 determines whether the data structure that contains the entries for the foreign servers can be protected so that multiple access to the data structure is prohibited. If not, e.g., if the protection mechanism fails, item 1126 reverses the accessing of the server segments through an internal API call and NERR.sub.-- InternalError is returned by termination block 1128. Decision 1130 determines Whether the server table entry is valid. If not, termination block 1132 performs a clear/free operation and returns error NERR.sub.-- NoSuchServer. Decision 1134 determines whether the connection I.D. is valid. If not, termination block 1136 performs a clear/free operation and returns error NERR.sub.-- NoSuchConnection. Decision 1138 determines whether the connection table entry is valid. If not, termination block 1140 performs a clear/free operation and returns error NERR.sub.-- NoSuchConnection. Item 1142 is invoked to release a semaphore to relinquish control of the data structure. Item 1144 then copies connection information to the parameter (buf) according to a level specified in parameter level. Item 1146 is invoked to release server segments by calling an internal API.

Referring now to FIGS. 12A to 12C, the I.sub.-- NetFileEntryMake API 1200 informs the central server that a new file entry has been established. It is used whenever a foreign server opens a file on the central server system. The data structure is set forth below:

When invoked, the process 1200 begins with item 1202, which performs error checking on the parameters passed to the central server, to determine whether the parameters reference is a legal location within memory. Decision 1204 then determines whether the network is installed and active. If not, a NERR.sub.-- NetNotStarted error code is returned to the caller in termination block 1206. If decision 1204 determines the network is installed and active, control passes to decision 1208, which determines whether the caller has authority to invoke the API 1200. If not, a ERROR.sub.-- NETWORK.sub.-- ACCESS.sub.-- DENIED error code is returned to the caller in termination block 1210. If decision 1208 determines the caller has authority to proceed in the API 1200, control passes to decision 1216, which determines whether the data structure level of detail is zero. If not, error ERROR.sub.-- INVALID.sub.-- LEVEL is returned by termination block 1218. Decision 1220 determines whether the data strings within the buffer buf, and passed in as a parameter, are valid. If not, termination block 1120 returns ERROR.sub.-- INVALID.sub.-- PARAMETER. Decision 1224 determines whether the caller can access the central server memory. If not, error NERR.sub.-- ServerNotStarted is returned by termination block 1226. Decision 1228 determines whether the data structure that contains the entries for the foreign servers can be protected so that multiple access to the data structure is prohibited. If not, e.g., if the protection mechanism fails, item 1230 reverses the accessing of the server segments through an internal API call and NERR.sub.-- InternalError is returned by termination block 1232. Decision 1234 determines whether the parameter server.sub.-- id (server identification code) is valid. If not, termination block 1236 returns NERR.sub.-- NoSuchServer. Decision 1238 determines whether the server table entry is valid. If not, termination block 1240 performs a clear/free operation and returns error NERR.sub.-- NoSuchServer. Decision 1242 determines whether the connection I.D. is valid. If not, termination block 1243 performs a clear/free operation and returns error NERR.sub.-- NoSuchConnection. Decision 1246 determines whether the connection table entry is valid. If not, termination block 1248 performs a clear/free operation and returns error NERR.sub.-- NoSuchConnection. Decision 1250 determines whether the number of files exceed a predetermined maximum value. If so, termination block 1252 performs a clear/free operation and returns NERR.sub.-- TooManyFiles. If the number of files is less than a predetermined maximum value, item 1254 allocates a new file table entry. If the allocation fails, item 1254 first logs the error, performs a clear/free operation and returns ERROR.sub.-- NOT.sub.-- ENOUGH.sub.-- MEMORY. Item 1256 then initializes the file table entry. Item 1258 then updates the foreign server statistics. Item 1260 is invoked to release a semaphore to relinquish control of the data structure. Item 1262 is invoked to release server segments by calling an internal API.

Referring now to FIGS. 13A and 13B, the I.sub.-- NetFileEntryClear API 1300 removes a file entry from the file table. It is used to inform the central server that a particular file entry is no longer of interest. The data structures used with this API are set forth below:

When invoked, decision 1302 determines whether the network is installed and active. If not, a NERR.sub.-- NetNotStarted error code is returned to the caller in termination block 1304. If decision 1302 determines the network is installed and active, control passes to decision 1306, which determines whether the caller has authority to invoke the API 1300. If not, a ERROR.sub.-- NETWORK.sub.-- ACCESS.sub.-- DENIED error code is returned to the caller in termination block 1308. If decision 1306 determines the caller has authority to proceed in the API 1300, control passes to decision 1310, which determines whether the parameter server.sub.-- id (server identification code) is valid. If not, termination block 1312 returns NERR.sub.-- NoSuchServer. Decision 1314 determines whether the caller can access the central server memory. If not, error NERR.sub.-- ServerNotStarted is returned by termination block 1316. Decision 1318 determines whether the data structure that contains the entries for the foreign servers can be protected so that multiple access to the data structure is prohibited. If not, e.g., if the protection mechanism fails, item 1320 reverses the accessing of the server segments through an internal API call and NERR.sub.-- InternalError is returned by termination block 1322. Decision 1324 determines whether the server table entry is valid. If not, termination block 1326 performs a clear/free operation and returns error NERR.sub.-- NoSuchServer. Decision 1328 determines whether the file identification number is valid. If not, termination block 1330 performs a clear/free operation and returns error NERR.sub.-- FileIdNotFound. Otherwise, item 1332 deletes the file table entry, as the file is no longer active. Item 1334 then updates the foreign server statistics in the relevant tables, e.g., in the session and communication tables, etc. Item 1336 is invoked to release a semaphore to relinquish control of the data structure. Item 1338 is invoked to release server segments by calling an internal API call.

Referring now to FIGS. 14A to 14C, the I.sub.-- NetFileEntrySetInfo API 1400 allows a foreign server to set file table information in the central server. This is typically used to set information, such as the number of locks on a file, or to set the user level of a file. The data structure for this API is set forth below:

When invoked, the process 1400 begins with item 1402, which performs error checking on the parameters passed to the central server, to determine whether the parameters reference is a legal location within memory. Decision 1404 then determines whether the network is installed and active. If not, a NERR.sub.-- NetNotStarted error code is returned to the caller in termination block 1406. If decision 1404 determines the network is installed and active, control passes to decision 1408, which determines whether the caller has authority to invoke the API 1400. If not, a ERROR.sub.-- NETWORK.sub.-- ACCESS.sub.-- DENIED error code is returned to the caller in termination block 1410. If decision 1408 determines the caller has authority to proceed in the API 1400, control passes to decision 1412, which determines whether the data structure level of detail is zero. If not, error ERROR.sub.-- INVALID.sub.-- LEVEL is returned by termination block 1414. Decision 1416 then determines whether the parameter parmnum (parameter number) is valid. If not, termination block 1418 returns error ERROR.sub.-- INVALID.sub.-- PARAMETER. Decision 1420 determines whether the buffer length parameter passed to the API is correct. If not, error NERR.sub.-- BufTooSmall is returned by termination block 1422. Decision 1424 determined whether the parameter server.sub.-- id (server identification code) is valid. If not, termination block 1426 returns NERR.sub.-- NoSuchServer. Decision 1428 determined whether the caller can access the central server memory. If not, error NERR.sub.-- ServerNotStarted is returned by termination block 1430. Decision 1432 determines whether the data structure that contains the entries for the foreign servers can be protected so that multiple access to the data structure is prohibited. If not, e.g., if the protection mechanism fails, item 1434 reverses the accessing of the server segments through an internal API call, and NERR.sub.-- InternalError is returned by termination block 1436. Decision 1438 determines whether the server table entry is valid. If not, termination block 1440 performs a clear/free operation and returns error NERR.sub.-- NoSuchServer. Decision 1442 determined whether the file identification number is valid. If not, termination block 1444 performs a clear/free operation and returns error NERR.sub.-- FileIdNotFound. Otherwise, item 1446 sets the file table entry according to the parameter (parmnum). Item 1448 is invoked to release a semaphore to relinquish control of the data structure. Item 1450 is invoked to release server segments by calling an internal API.

Referring now to FIGS. 15A and 15B, the I.sub.-- NetFileEntryGetInfo API 1500 is used to retrieve file table information from the central servers file table to determine the status of a file on the central server. The data structures used by this API are set forth below:

When invoked, the process 1500 begins with item 1502, which performs error checking on the parameters passed to the central server, to determine whether the parameters reference is a legal location within memory. Decision 1504 then determines whether the network is installed and active. If not, a NERR.sub.-- NetNotStarted error code is returned to the caller in termination block 1506. If decision 1504 determines the network is installed and active, control passes to decision 1508, which determines whether the caller has authority to invoke the API 1500. If not, a ERROR.sub.-- NETWORK.sub.-- ACCESS.sub.-- DENIED error code is returned to the caller in termination block 1510. If decision 1508 determines the caller has authority to proceed in the API 1500, control passes to decision 1512, which determines whether the data structure level of detail is zero. If not, error ERROR.sub.-- INVALID.sub.-- LEVEL is returned by termination block 1514. Decision 1516 determines whether the parameter server.sub.-- id (server identification code) is valid. If not, termination block 1518 returns NERR.sub.-- NoSuchServer. Decision 1520 determines whether the caller can access the central server memory. If not, error NERR.sub.-- ServerNotStarted is returned by termination block 1522. Decision 1524 determines whether the data structure that contains the entries for the foreign servers can be protected so that multiple access to the data structure is prohibited. If not, e.g., if the protection mechanism fails, item 1526 reverses the accessing of the server segments through an internal API call, and NERR.sub.-- InternalError is returned by termination bock 1528. Decision 1530 determines whether the server table entry is valid. If not, termination block 1532 performs a clear/free operation and returns error NERR.sub.-- NoSuchServer. Decision 1534 determines whether the file identification number is valid. If not, termination block 1536 performs a clear/free operation and returns error NERR.sub.-- FileIdNotFound. Item 1538 is invoked to release a semaphore to relinquish control of the data structure. Item 1540 copies the file information stored in the file table maintained by the central server to buffer buf, according to the specified level (level). Item 1542 is invoked to release server segments by calling an internal API.

FIG. 16 is a flow diagram of the clear/save operation performed by various APIs of the present invention. This operation is performed to reverse any actions of an API which fails during any point in its execution. Item 1602 is invoked to release a semaphore sd.sub.-- asdsem to relinquish control of the foreign server data structure 1600. Item 1604 is invoked to release server segments by calling an internal API.

FIG. 17 is a flow diagram of the allocate operation performed by various APIs of the present invention. When invoked, item 1702 allocates a new data structure, such as a table entry. Decision 1704 determines whether the allocation attempt of item 1702 failed. If decision 1704 fails, i.e., the allocation attempt of item 1702 fails, item 1706 logs the error ERROR.sub.-- NOT.sub.-- ENOUGH.sub.-- MEMORY for the user. Item 1708 then performs the clear/free operation 1600 and returns error ERROR.sub.-- NOT.sub.-- ENOUGH.sub.-- MEMORY. If decision 1704 succeeds, i.e., the allocation attempt of item 1702 succeeds, control flow then passes to the relevant point in the API which calls process 1700.

In summary, an improved method and means for networking computers having varying file architectures has been described. In accordance with the principles of the present invention, a file server network comprises a central file server and one or more foreign servers. Each of the respective central and foreign file servers is provided with its own file system. The file system of the central server is available to and directly accessed by the foreign servers without any interaction from the central file server. The present invention further includes a method and means for advising the central file server of activities of the foreign servers wherein the central file server may be used for both system administration and system monitoring functions. Accordingly, other uses and modifications of the present invention will be apparent to persons of ordinary skill in the art and all of such uses and modifications are anticipated by the appended claims.