Abstract:
The invention is directed to techniques for accessing a data storage system having both a filesystem and directory system. In one arrangement, an apparatus has memory that stores an application, and a controller coupled to the memory. The controller operates in accordance with the application stored in the memory to access a data storage system. In particular, the application configures the controller to obtain an access instruction which identifies a portion of the data storage system, and determine, in response to the obtained access instruction, whether the identified portion of the data storage system is a file of the filesystem or a directory entry of the directory system. The application further configures the controller to perform a file access operation to access the identified portion as a file when the identified portion is determined to be a file of the filesystem, and a directory entry access operation to access the identified portion as a directory entry when the identified portion is determined to be a directory entry of the directory system. Since the apparatus is capable of determining whether the access instruction identifies a file of a filesystem or a directory entry of a directory system, application developers need not be concerned about the availability of any particular vendor-specific APIs. Rather, the application developers can simply use an access instruction with a common syntax and expression such as that for accessing a file of UNIX filesystem (e.g., open( ), read( ), write( ), etc.), and let the apparatus determine how to handle such instructions.

Description:
BACKGROUND OF THE INVENTION 
     Some application developers develop applications which perform data storage and retrieval operations. To this end, an application developer typically writes application source code which includes data storage and/or retrieval commands using a programming language (e.g., the C programming language). In general, the application developer builds an executable application from the application source code (e.g., by compiling and linking the application source code). This executable application contains instructions that run on a computer system to store data within and/or retrieve data from memory of the computer system. 
     By way of example, FIG. 1 shows a computer system  20  which includes a first computer  22 -A, a second computer  22 -B, and a network connection  24  allowing communication between the first and second computers  22 -A,  22 -B. Each of the first and second computers  22 -A,  22 -B includes a filesystem. In particular, the first computer  22 -A includes a UNIX filesystem  26 -A. Similarly, the second computer  22 -B includes a UNIX filesystem  26 -B. As shown in FIG. 1, each of the UNIX filesystems  26 -A,  26 -B includes files which are logically organized in an inverted tree configuration. 
     The second computer  22 -B further includes a directory system. In particular, as shown in FIG. 1, the second computer  22 -B has a Lightweight Directory Access Protocol (LDAP) directory system  28 -B and operates as an LDAP server. The LDAP directory system  28 -B includes directory entries which are organized in an inverted tree configuration which is similar to that of the UNIX filesystems  26 -A,  26 -B. Directory systems are similar to databases in that they operate as repositories, or storage facilities, for information. However, in contrast to databases, directory systems tend to contain more descriptive, attribute-based information (e.g., names, addresses, job titles, etc.). Furthermore, information is generally more often read from such directory systems than written to such directory systems. 
     FIG. 2A shows application code  30  having commands for accessing the filesystem  26 -A of the first computer  22 -A. In particular, the application code  30 , when compiled and linked into an executable application, provides instructions for retrieving information  32  from a file  34  of the filesystem  26 -A. 
     To create application code for accessing UNIX filesystems, application developers can use file access commands in the C programming language. In general, such commands have standardized names (e.g., “open( )”, “write( )”, “read( )”, “getline( )”, “close( )”, etc.) and standardized expression formats (e.g., operation(arg 1 , . . . ,argN)). 
     Some application developers develop applications which conform to a programming standard called POSIX, which is an acronym for portable operating system interface for computer environments. By conforming application code to the POSIX programming standard, the application developer has some assurance that the application will be relatively easily portable to POSIX-compliant computer systems. Sun Microsystems, Inc. of Palo Alto, Calif., International Business Machines Corporation of Armonk, N.Y., and Hewlett-Packard of Palo Alto, Calif. are examples of computer manufacturers which provide POSIX-compliant computer systems. 
     It should be understood that there are other filesystems which can be used for storing and retrieving data. Examples of other filesystems include the MS-DOS filesystem and the Windows/NT filesystem, both of which are provided by Microsoft Corporation of Redmond, Wash. 
     Furthermore, it should be understood that some computer systems provide access to multiple types of filesystems. For example, some computer systems running the UNIX operating system can be configured to provide access to both a UNIX filesystem and a Windows/NT filesystem. In general, when applications run in such a computer system, the operating system handles application instructions (e.g., system calls) which request access to files of the different filesystems. Typically, when a running application reaches a file access instruction (e.g., open( )), the operating system figures out which type of filesystem the file access instruction is attempting to access (i.e., UNIX or Windows/NT in this example), and then performs one or more file access operations which are appropriate for accessing that type of filesystem. 
     FIG. 2B shows application code  40  having commands for accessing the LDAP directory system  28 -B of the second computer  22 -B (an LDAP server). In particular, the application code  40 , when compiled and linked into an executable application, provides instructions for retrieving information  42  from an LDAP directory entry  44  of the LDAP directory system  28 -B. Generally, the computer system  52 -B operates as an LDAP server such that an executable application derived from the application code  40  can run on any of the computers  22  as an LDAP client communicating with the LDAP server. 
     To create application code for accessing directory systems, an application developer typically obtains a development environment package from a provider or manufacturer of a directory system product (hereinafter referred to as a vendor). Such a package typically includes a vendor-specific application programming interface (API) for developing an application, and a directory system server platform having a suite of services, utilities and tools for testing the application. In general, the application developer includes, in the application code, directory access commands (e.g., “ldap_search( )”, “ldap_entry( )”, “Idap_first_attribute( )”, “ldap_next 13  attribute( )”, etc.) which conform to the vendor-specific API. In the case of LDAP directory systems, such code typically relies on manipulating LDAP information such as directory entry locations, port numbers, etc. 
     Additionally, it is common for such commands to have unique, vendor-specific names and expressions. Examples of LDAP directory system vendors include the University of Michigan of Ann Arbor, Mich., Sun Microsystems, Inc. of Palo Alto, Calif., International Business Machines Corporation of Armonk, N.Y., and Netscape Communications Corporation of Mountain View, Calif. By way of example, the command for performing a bind function using ADSI, which is provided by Microsoft Corporation of Redmond, Wash., is similar to: 
     AdsOpenObject(“LDAP://server/en=bols,o=company . . . ). 
     In contrast, the command for performing a bind function using NDS, which is provided by Novell of Orem, Utah, is similar to: 
     NWDSLogin(context,o,UserName,UserPassword,o). 
     Accordingly, LDAP expressions can vary greatly among vendors. 
     SUMMARY OF THE INVENTION 
     Applications which access directory systems using vendor-specific APIs are often hindered by unique aspects of such APIs. For example, it is common for LDAP vendors to require unique names and expressions for particular LDAP commands. That is, application developers must use these unique names and expressions in order to properly program an application to a particular LDAP vendor&#39;s API. Accordingly, the application developer of an application often relies on each customer having a particular LDAP server product also installed on computer systems running the application developer&#39;s application. Otherwise, it may be possible for the application to include one or more LDAP commands (e.g., ldap_open( ), ldap_create( ), ldap_read( ), etc.) or command expressions (e.g., Idap_open(arg 1 ,arg 2 ) vs. Idap_open(*argl,*arg 2 )) which the computer system cannot understand or handle. 
     In situations where the LDAP product of a particular LDAP vendor is unavailable but the LDAP product of another LDAP vendor is available, the application developer may be able to port the LDAP application such that it is able to use the other LDAP product. However, in some situations, applications are not easily portable and require significant code changes when switching between different vendor-specific APIs. Furthermore, if even only minor code changes are required, the porting process still requires recompiling and relinking of the application, and often thorough retesting. Moreover, such an endeavor often requires that the application developer provide future technical support for both the original application (which works with the original vendor-specific API) as well as any newly ported application (which works with the new vendor-specific API) in order to maintain goodwill, and the perception of quality and good service among customers. 
     In contrast to the above-identified approaches to accessing LDAP directory systems using different vendor-specific APIs, the invention is directed to techniques for accessing a data storage system having both a filesystem and directory system by determining, in response to an instruction for accessing a portion of the data storage system, whether the portion is a file of the filesystem or a directory entry of the directory system, and then accessing that portion of the data storage system appropriately. Accordingly, application developers can use commands with common or standard names and expressions, such as those for accessing files of filesystems (e.g., POSIX calls), and rely on the above-identified determination (e.g., performed by the operating system of a computer) for proper operation and processing of the application. 
     One arrangement of the invention is directed an apparatus having memory that stores an application, and a controller that is coupled to the memory. The controller operates in accordance with the application stored in the memory to access a data storage system. The data storage system includes a filesystem and a directory system. The application configures the controller to perform a method having the steps of: (a) obtaining an access instruction which identifies a portion of the data storage system, and (b) determining, in response to the obtained access instruction, whether the identified portion of the data storage system is a file of the filesystem or a directory entry of the directory system. The method further includes the step of: (c) performing a file access operation to access the identified portion as a file when the identified portion is determined to be a file of the filesystem, and a directory entry access operation to access the identified portion as a directory entry when the identified portion is determined to be a directory entry of the directory system. 
     Since the apparatus is capable of determining whether the access instruction identifies a file of a filesystem or a directory entry of a directory system, application developers need not be concerned about the availability of any particular vendor-specific APIs. Rather, the application developers can simply use an access instruction with a common syntax and expression such as that for accessing a file of filesystem (e.g., open( ), read( ), write( ), etc.), and let the apparatus (e.g., specialized hardware, a computer, etc.) determine how to handle such instructions. 
     In one arrangement, the filesystem is a UNIX filesystem, and the directory system is a Lightweight Directory Access Protocol directory system. In this arrangement, the step of performing includes the step of accessing the identified portion of the data storage system as (i) a UNIX file when the identified portion is determined to be a file of the filesystem, or (ii) a Lightweight Directory Access Protocol (LDAP) directory entry when the identified portion is determined to be a directory entry of the directory system. 
     In one arrangement, the method further includes, prior to the step of performing the access operation, the step of mounting a directory entry of the LDAP directory system to a mount point of the UNIX filesystem in order to couple the Lightweight Directory Access Protocol directory system to the UNIX filesystem. Preferably, the directory system mounts beneath the mount point of the filesystem. Such mounting couples the directory system to the filesystem. Accordingly, a user of the apparatus can then navigate among the directory system in a manner similar to that for navigating around a filesystem (e.g., using “cd” to change current directories when navigating within a UNIX filesystem). 
     In one arrangement, the step of determining includes the step of ascertaining a location of the identified portion of the data storage system relative to the mount point. of the UNIX filesystem. This allows enables the controller to determine whether the identified portion of the data storage system is a file of the filesystem or a directory entry of the directory system. For example, if the identified portion of the data storage system resides below the mount point in an inverse-hierarchical arrangement between the UNIX filesystem (which includes the root, “/”) and the directory system, the identified portion is a directory entry of the directory system. However, if the identified portion is above the mount point, the identified portion is a file of the UNIX filesystem. 
     In an alternative arrangement, each file of the filesystem belongs to a file object class, and each directory entry of the directory system belongs to a directory entry object class. In this arrangement, the step of determining includes the step of deciding whether the identified portion belongs to the file object class or the directory entry object class. Accordingly, the controller can determine whether the identified portion is a UNIX file or LDAP directory entry. 
     In one arrangement, the access instruction is an open command, and the step of performing includes the step of carrying out, based on a result of the step of determining, one of a UNIX open operation and an LDAP open operation to open the identified portion of the data storage system. 
     In another arrangement, the access instruction is a create command, and the step of performing includes the step of carrying out, based on a result of the step of determining, one of a UNIX create operation and an LDAP create operation to create the identified portion of the data storage system. 
     In another arrangement, the access instruction is an unlink command, and the step of performing includes the step of carrying out, based on a result of the step of determining, one of a UNIX remove operation and an LDAP delete operation to erase the identified portion from the data storage system. 
     In another arrangement, the access instruction is a read command, and the step of performing includes the step of carrying out, based on a result of the step of determining, one of a UNIX read operation and an LDAP read operation to read data from the identified portion of the data storage system. 
     In another arrangement, the access instruction is a write command, and the step of performing includes the step of carrying out, based on a result of the step of determining, one of a UNIX write operation and an LDAP write operation to write data to the identified portion of the data storage system. 
     In another arrangement, the access instruction is a readdir command, and the step of performing includes the step of carrying out, based on a result of the step of determining, one of a UNIX readier operation and an LDAP readdir operation to obtain information regarding the identified portion of the data storage system (e.g., current location information when navigating around the data storage system). 
     Another arrangement of the invention is directed to a computer program product that includes a computer readable medium having instructions stored thereon for accessing a data storage system. The data storage system includes a filesystem and a directory system. The instructions, when carried out by the computer, cause the computer to perform the steps of: (a) obtaining an access instruction which identifies a portion of the data storage system; (b) determining, in response to the obtained access instruction, whether the identified portion of the data storage system is a file of the filesystem or a directory entry of the directory system; and (c) performing a file access operation to access the identified portion as a file when the identified portion is determined to be a file of the filesystem, and a directory entry access operation to access the identified portion as a directory entry when the identified portion is determined to be a directory entry of the directory system. 
     The directory system can be used as a repository for network information such as network configuration data and policy definitions. Application developers can then develop network applications which use an API having a file-like interface (i.e., file-like command names and expressions) to access the network information in entries of the directory system. In one arrangement, entries of the directory system are accessible using an interface of POSIX or POSIX-like names and expressions (e.g., open( ), read( ), write( ), etc.). Accordingly, in situations where the application developer knows a priori a location in the data storage system, an elaborate search filter is not required and the application developer can use familiar file-like system calls (e.g., open( ), read( ), write( ), etc.) to access the network information. The features of the invention, as described above, may be employed in data communications devices and other computerized devices such as those manufactured by Cisco Systems, Inc. of San Jose, Calif. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
     FIG. 1 (prior art) is a block diagram showing a conventional computer system having a first computer which stores a UNIX filesystem, and a second computer which stores a UNIX filesystem and a Lightweight Directory Access Protocol (LDAP) directory system. 
     FIG. 2A (prior art) is a block diagram showing a conventional approach for accessing data from a file of one of the UNIX filesystems of FIG.  1 . 
     FIG. 2B (prior art) is a block diagram showing a conventional approach for accessing data from a directory entry of the LDAP directory system of FIG.  1 . 
     FIG. 3 is a block diagram showing a computer system which has a data storage system that includes a UNIX filesystem and a LDAP directory system which is suitable for use by the invention. 
     FIG. 4 is a block diagram showing a technique for accessing the data storage system of FIG.  3 . 
     FIG. 5 is a block diagram showing a computer which is suitable for use as a computer of the computer system of FIG.  3 . 
     FIG. 6 is a flowchart showing a mount procedure which is suitable for use by a computer of the computer system of FIG.  3 . 
     FIG. 7 is a flowchart showing an open procedure which is suitable for use by a computer of the computer system of FIG.  3 . 
     FIG. 8 is a flowchart showing a create procedure which is suitable for use by a computer of the computer system of FIG.  3 . 
     FIG. 9 is a flowchart showing an unlink procedure which is suitable for use by a computer of the computer system of FIG.  3 . 
     FIG. 10 is a flowchart showing a read procedure which is suitable for use by a computer of the computer system of FIG.  3 . 
     FIG. 11 is a flowchart showing a write procedure which is suitable for use by a computer of the computer system of FIG.  3 . 
     FIG. 12 is a flowchart showing a readdir procedure which is suitable for use by a computer of the computer system of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention is directed to techniques for accessing a data storage system having both a filesystem and directory system by determining, in response to an instruction for accessing a portion of the data storage system, whether the portion is a file of the filesystem or a directory entry of the directory system, and then accessing that portion of the data storage system appropriately. Accordingly, an application developer can develop an application having commands with common or standard names and expressions, such as those for accessing files of filesystems (e.g., using the same syntax as that for POSIX calls), and rely on this determination (e.g., performed by the operating system of a computer) for proper operation and processing of the application. Such an application will be more portable than applications which rely on vendor-specific APIs, e.g., Lightweight Directory Access Protocol (LDAP) APIs such as the LDAP C, ADSI and CNS/AD APIs. In particular, such an application can access directory entries using a file-like API (e.g., POSIX-like) and not worry about manipulating LDAP information such as directory entry locations, port numbers, etc. 
     FIG. 3 shows a computer system  50  which is suitable for use by the invention. The computer system  50  includes a first computer  52 -A, a second computer  52 -B, a third computer  52 -C, and a network connection  54  which enables the computers  52 -A,  52 -B,  52 -C to communicate. The computers  52 -A,  52 -B,  52 -C (collectively, the computers  52 ) include respective UNIX filesystems  56 -A,  56 -B,  56 -C (collectively, the filesystems  56 ). The computer  52 -B further includes an LDAP directory system  58 -B. 
     As shown in FIG. 3, the UNIX filesystems  56  include files  60  which are organized logically into an inverted tree configuration. Similarly, the LDAP directory system  58 -B includes directory entries  62  which are organized logically into an inverted tree configuration. An LDAP directory entry  62  of the LDAP directory system  58 -B is logically coupled with a file  60 , i.e., a mount point, of the UNIX filesystem  56 -A, as illustrated in FIG. 3 by the dashed line  64 , i.e., a mount relationship. This mount situation is similar to a network filesystem (NFS) mount in that a data storage system (namely, an LDAP directory system) of one computer (i.e., computer  52 -B) is mounted to a mount point of another computer (i.e., computer  52 -A) through the network connection  54 . 
     In the arrangement of FIG. 3, any of the computers  52  can view and access the LDAP directory system  58 -B. For example, the computer  52 -B can view and access the LDAP directory system  58 -B locally. Additionally, the computers  52 -A and  52 -C can view and access the LDAP directory system  58 -B remotely. In particular, any of the computers  52  can view and access the LDAP directory system  58 -B by navigating or traversing a data storage system  70  (FIG. 4) formed by the UNIX filesystem  52 -A and the LDAP directory system  58 -B. That is, the directory entries (or entries) of the directory system  58 -B are visible below the mount point as files of the filesystem  52 -A. Furthermore, in accordance with the invention, data within the directory entries are accessible using file-like system calls. Alternatively, applications can operate as LDAP clients and communicate with the computer  52 -B as an LDAP server in a typical LDAP manner. Further details of these features of the invention will now be described with reference to FIGS. 4 and 5. 
     FIG. 4 shows a logical diagram of the data storage system  70  formed by the UNIX files system  56 -A of the computer  52 -A, and the LDAP directory system  58 -B of the computer  52 -B. In particular, the UNIX filesystem  56 -A includes multiple files such as the root  72  (called “/”) and a file  74  (called “directory”). The directory system  58 -B includes multiple directory entries including an LDAP directory entry  76  (called “ou=people”) and another LDAP directory entry  78  (called “uid=dsmith”). The LDAP directory entry  76  logically mounts to a mount point under the UNIX file  74  to maintain an inverted tree configuration for the data storage system  70 . 
     Preferably, a user or an application can navigate around files and mounted LDAP directory entries of the data storage system  70  in a manner similar to that for navigating a filesystem. In the arrangement of FIG. 4, and by way of example only, a user can perform standard UNIX navigation operations such as listing child nodes beneath a current location (e.g., “ls”) and changing from one current location to another (e.g., “cd”. As another example, an application developer can develop application code  80  which includes common file access commands (e.g., “open( )”) to access data within one or more LDAP directory entries. As shown in FIG. 4, application code  80 , which uses commands having standard file access command names and expressions, can be compiled and linked to generate an executable application having instructions which access data  82  from an LDAP directory entry  78  based on those commands. Further details of this feature of the invention will now be provided with reference to FIG.  5 . 
     FIG. 5 shows a computer  90  which is suitable for use as any of the computers  52  of the computer system  50  of FIG.  3 . The computer  90  includes a network interface  92  (e.g., for interfacing with the network connection  54 ), memory  94  and a processor  96 . The memory  94  consists of several memory constructs such as an application  98  and an operating system  100 . The operating system  100  includes, among other things, a mount list  102  and an interface  104  (e.g., a system call interface). 
     The memory  94  may further include other memory constructs such as a filesystem  106  and a directory system  108 . For example, each of the computers  52 -A,  52 -C includes a respective UNIX filesystem  56 -A,  56 -C, but does not include a directory system (see FIG.  3 ). Additionally, the computer  52 -B (an LDAP server) includes both a UNIX filesystem  56 -B and an LDAP directory system  58 -B. 
     In one arrangement, a computer program product  110  (e.g., one or more CDROMs, tapes, diskettes, etc.) provides one or more of the above-described memory constructs to the computer  90 . For example, the computer program product  110  may include both the application  98  and the operating system  100 . In this example, the operating system  100  and the application  98  can be installed on the computer  90 , and then invoked to create other memory constructs such as the directory system  108 . The Cisco IOS manufactured by Cisco Systems of San Jose, Calif. is suitable for use as the operating system  100 . As an alternative example, the computer  90  can acquire the application  98  through other means, e.g., via a network download through the network interface  92 . 
     The operating system  100  supports a directory storage system  108  with object-classes (e.g., a directory entry object class) which enables the operating system  100  to treat directory entries of the directory system in a file-like manner. Furthermore, the directory entries, which are to be treated in the file-like manner by the operating system, include a “whole data” attribute. As such, when the operating system  100  accesses a portion of a data storage system having both files and directory entries and determines that the portion is a directory entry, the operating system  100  can provide information from the directory entry in LDAP Data Interchange Format (LDIF), a popular format that describes directory entry information as text files. However, if the directory entry has a different object class (e.g., a file object class), the controller  111  can provide the information in a different, non-LDIF format (e.g., store a file in the directory entry). This mechanism of storing files in a directory system can be made into a standard through the Internet Engineering Task Force (IETF) LDAP extension group. 
     During operation, the processor  96  runs the operating system  100  to form a controller  111  which processes instructions  112  (e.g., application instructions, command line user instructions, etc.). The controller  112  includes a determining module  114  and an operation performing module  116 . The determining module  114  determines, for each data access instruction (e.g., open( ), read( ), write( ), etc.) of the instructions  112 , whether that data access instruction targets a file of a filesystem (e.g., files  72 ,  74  in FIG. 4) or a directory entry of a directory system (e.g., directory entries  76 ,  78  in FIG.  4 ). The determining module  114  then provides a signal  118  to the operation performing module  116  indicating whether that data access instruction targets such a file or a directory entry. The operation performing module  116  executes the instructions  112 . In particular, when the operation performing module  116  executes the data access instructions, the module  116  performs data access operations based on the signal  118  which indicates whether the data access instructions target files or directory entries. Accordingly, application developers can develop applications (e.g., the application  98 ) which use a file-like interface to access information (e.g., network information) within a directory system (e.g., the directory system  108 ). 
     FIG. 6 shows a procedure  120  that is performed by the controller  111  when encountering a mount request (e.g., a mount system call). In step  122 , the controller  111  receives the mount request identifying (i) a mount point of a filesystem and (ii) a mount target. 
     In step  124 , the controller  111  determines whether the mount target is a directory entry of a directory system or a file of a filesystem. In one arrangement, the controller  111  checks an object class (or datatype) of the mount target to make this determination. If the mount target is a file of a filesystem, step  124  proceeds to step  126 . If the mount target is a directory entry of a directory system, step  124  proceeds to step  128 . 
     In step  126 , the controller  111  has determined the mount target to be a file of a filesystem and mounts the file to the mount point. In particular, the controller  111  performs this mount operation in a conventional manner by establishing a mount relationship within an entry of the mount list  102  of the computer  90  (see FIG.  5 ), e.g., a POSIX mount( ) operation. 
     In steps  128  through  132 , the controller  111  has determined the mount target to be a directory entry of a directory system, and mounts the directory entry to the mount point. In step  128 , the controller  111  initializes an LDAP server for operation (e.g., by performing an ldap_init( ) operation). In step  130 , the controller  111  preferably performs a login operation for authentication purposes (e.g., by performing an ldap_bind( ) operation). Then, in step  132 , the controller  111  updates the mount list  102  of the filesystem. Accordingly, the directory system is mounted to the filesystem. 
     Once the controller  111  completes the procedure  120  thus mounting the directory system to the filesystem, the directory system is essentially integrated into the global name space of the filesystem from the perspective of the operating system  100 . Accordingly, an interactive file-manager running on the computer  90 , which shows the filesystem in an inverted tree hierarchy, will logically show (to a user) the directory entries of the directory system as files. As such, double-clicking on a directory entry (which the file-manager displays as a file) will make information within the directory entry available to the user (e.g., in LDIF format). A directory browser can also access the directory entries of the directory system but such a browser is no longer required. 
     With reference to FIGS. 3 through 6 and by way of example, when mounting the directory system  58 -B to the filesystem  56 -A (see FIG.  3 ), the mount point is a file called “people” of the filesystem  56 -A, and the mount target is an LDAP directory entry called “ou=people” of the LDAP directory system  58 -B. The application  98  running on the computer  90  (see FIG. 5) provides the controller  111  with a mount request (step  122 ). The determining module  114  determines that the mount target of the request is an LDAP directory entry (step  124 ), and provides the signal  116  indicating that the mount target is an LDAP directory entry. Based on the signal  116 , the operation performing module  118  then initializes an LDAP server (e.g., part of the operating system  100 ), binds the LDAP directory entry, and mounts the mount target (the directory entry called “ou=people”) to the mount point (steps  128  through  132 ). Upon completion of the mount operation, the filesystem  56 -A and the directory system  58 -B form the data storage system  70 , which is logically illustrated in FIGS. 4 and 3. 
     FIG. 7 shows a procedure  140  which is performed by the controller  111  when  10  encountering an open request (e.g., an open( ) system call). In step  142 , the controller  111  receives the open request which identifies a portion of the data storage system  70  including the UNIX filesystem  56 -A and LDAP directory system  58 -B. 
     In step  144 , the controller  111  determines whether the identified portion of the data storage system  70  is a UNIX file or an LDAP directory entry. If the identified portion is a UNIX file, step  144  proceeds to step  146 . If the identified portion is an LDAP directory entry, step  144  proceeds to step  148 . 
     In step  146 , the identified portion is a UNIX file and the controller  111  opens the UNIX file in a conventional manner (e.g., a POSIX open( ) operation). In particular, the controller  111 , among other things, retrieves a file descriptor for identifying the file. 
     In step  148 , the identified portion is an LDAP directory entry and the controller  111  performs an LDAP open operation. In particular, the controller  111  initializes internal data structures for a file with a distinguished name of the directory entry of the directory system (e.g., “ou=people”, see FIGS.  3  and  4 ). Accordingly, the controller  111  has now opened the directory entry of the directory system for access by an application. 
     FIG. 8 shows a procedure  150  which is performed by the controller  111  when encountering a create request (e.g., a creates system call). In step  152 , the controller  111  receives the create request which identifies a portion of the data storage system  70  that includes the UNIX filesystem  56 -A and LDAP directory system  58 -B. 
     In step  154 , the controller  111  determines whether the identified portion of the data storage system  70  is a UNIX file or an LDAP directory entry. If the identified portion is a UNIX file, step  154  proceeds to step  156 . On the other hand, if the identified portion is an LDAP directory entry, step  154  proceeds to step  158 . 
     In step  156 , the identified portion is a UNIX file and the controller  111  creates the UNIX file in a conventional manner (e.g., a POSIX creates operation). 
     In step  158 , the identified portion is an LDAP directory entry and the controller  111  performs an LDAP add operation. In particular, the controller  111  adds an entry to the LDAP directory system of the data storage system  70 . The controller  111  distinguishes the entry from other entries by providing a unique attribute for the entry. Accordingly, the controller  111  has now added a directory entry to the directory system. 
     FIG. 9 shows a procedure  160  which is performed by the controller  111  when encountering an unlink request (e.g., an unlink system call). In step  162 , the controller  111  receives the unlink request identifying a portion of the data storage system  70  which includes the UNIX filesystem  56 -A and LDAP directory system  58 -B. 
     In step  164 , the controller  111  determines whether the identified portion of the data storage system  70  is a UNIX file or an LDAP directory entry. If the identified portion is a UNIX file, step  164  proceeds to step  166 . In contrast, if the identified portion is an LDAP directory entry, step  164  proceeds to step  168 . 
     In step  166 , the identified portion is a UNIX file and the controller  111  unlinks the UNIX file in a conventional manner. In particular, the controller  111  removes the UNIX file from the filesystem. 
     In step  168 , the identified portion is an LDAP directory entry and the controller  111  performs an LDAP delete operation. In particular, the controller  111  deletes an existing entry to the LDAP directory system of the data storage system  70 . Accordingly, the controller  111  has now removed the directory entry from the directory system. 
     FIG. 10 shows a procedure  170  which is performed by the controller  111  when encountering a read request (e.g., a read( ) system call). In step  172 , the controller  111  receives the read request which identifies a portion of the data storage system  70  including the UNIX filesystem  56 -A and LDAP directory system  58 -B. 
     In step  174 , the controller  111  determines whether the identified portion of the data storage system  70  is a UNIX file or an LDAP directory entry. If the identified portion is a UNIX file, step  174  proceeds to step  176 . Otherwise, if the identified portion is an LDAP directory entry, step  174  proceeds to steps  178  through  188 . 
     In step  176 , the identified portion is a UNIX file and the controller  111  reads data from the UNIX file in a conventional manner (e.g., a POSIX read( ) operation). 
     In steps  178  through  188 , the controller  111  reads data from the LDAP directory entry. In step  178 , the controller  111  performs an LDAP search (or filter) operation to find the identified directory entry within the LDAP directory system. In step  180 , the controller  111  performs an LDAP first entry operation to obtain the identifier (ID) of the LDAP directory entry (also referred to as an LDAP entry). In step  182 , the controller  111  performs an LDAP first attribute operation to obtain the first attribute of the LDAP entry identified by the identifier obtained in step  180 . In step  186 , the controller  111  can obtain additional attributes by performing LDAP next attribute operations. In step  188 , the controller  111  gets values from the identified LDAP entry. The result of performing steps  178  through  188  is data which has been extracted from an LDAP entry in a manner that is transparent to the application  98  which provided the initial read instruction to the controller  111  (i.e., no need to specify whether target is LDAP entry or UNIX file). 
     In one arrangement, the controller  111  checks the object class of the LDAP entry prior to reading information from the entry. If the entry has a normal object class, the reads the information in LDAP Data Interchange Format (LDIF), a popular format that describes directory entry information as text files. However, if the directory entry has a different object class (e.g., a file object class), the controller  111  can store the information in a different, non-LDIF format (e.g., store a file in the directory entry). 
     FIG. 11 shows a procedure  190  which is performed by the controller  111  when encountering a write request (e.g., a write( ) system call). In step  192 , the controller  111  receives the write request which identifies a portion of the data storage system  70  having the UNIX filesystem  56 -A and LDAP directory system  58 -B. 
     In step  194 , the controller  111  determines whether the identified portion of the data storage system  70  is a UNIX file or an LDAP directory entry. If the identified portion is a UNIX file, step  194  proceeds to step  196 . However, if the identified portion is an LDAP directory entry, step  194  proceeds to steps  198  through  200 . 
     In step  196 , the identified portion is a UNIX file and the controller  111  writes data to the UNIX file in a conventional manner (e.g., a POSIX write( ) operation). 
     In steps  198  through  200 , the identified portion of the data storage system  70  is an LDAP entry. In step  198 , the controller  111  parses the information into an LDAP compatible format (e.g., converts a stream of bytes into a list of attributes and values). In step  200 , the controller  111  stores the parsed information in the LDAP directory entry by performing an LDAP modify operation (e.g., ldap_modify( )). Accordingly, the controller  111  has now written information into the directory entry of the directory system. 
     FIG. 12 shows a procedure  210  which is performed by the controller  111  when encountering a readdir request (e.g., a readdir( ) system call) to obtain information regarding a particular portion of the data storage system  70  (e.g., for the UNIX “ls” command). In step  212 , the controller  111  receives the readdir request which identifies the portion of the data storage system  70  having the UNIX filesystem  56 -A and LDAP directory system  58 -B. 
     In step  214 , the controller  111  determines whether the identified portion of the data storage system  70  is a UNIX file or an LDAP directory entry. If the identified portion is a UNIX file, step  214  proceeds to step  216 . On the other hand, if the identified portion is an LDAP directory entry, step  214  proceeds to steps  218  through  222 . 
     In step  216 , the identified portion is a UNIX file and the controller  111  obtains information regarding the UNIX file in a conventional manner (e.g., by performing low level operations for the UNIX “ls” command). 
     In steps  218  through  222 , the identified portion of the data storage system  70  is an LDAP entry. In step  218 , the controller  111  performs an LDAP search operation to find the LDAP entry within the LDAP directory system. In step  220 , the controller  111  performs an LDAP first entry operation to obtain an identifier (ID) of the LDAP entry. In step  222 , the controller  111  gets and returns values from the identified LDAP entry in order to satisfy the readdir request. Accordingly, the controller  111  has now obtained directory entry information of the directory system for use in navigating (e.g., for the “ls” and “cd” commands in UNIX) the data storage system as if it were exclusively a filesystem. 
     It should be understood that other types of requests (e.g., other system calls) can be configured to operate in manners similar to that described above for handling the more common types of access requests (e.g., open, create, read, write, etc. shown in FIGS.  6 - 12 ). By handling such requests using a file-like interface (e.g., POSIX-like), application developers can develop more portable applications (e.g., without relying on a particular LDAP API such as LDAP C, ADSI and CNS/AD). Additionally, the arrangement is well-suited for applications that access data such as network information (e.g., network configuration information and policy definitions), security and authentication data (e.g., passwords), and personnel information (e.g., names and addresses). The features of the invention may be particularly useful in computerized devices manufactured by Cisco Systems, Inc. of San Jose, Calif. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 
     For example, there is no set number of computers required for the invention. Three computer were shown in the arrangement of FIG. 3 by way of example only in order to illustrate a situation where any of the three computers will be able to access the data storage system  70  (also see FIG. 4) formed by the UNIX filesystem of the computer  52 -A and the LDAP directory system  58 -B of the computer  52 -B. Other arrangements may include different numbers of computers. For example, another arrangement may include a single computer having both a filesystem and a directory system in a local memory (e.g., disk memory, semiconductor memory, etc.). 
     Additionally, it should be understood that the topology of the computer system  50  is provided by way of example only. Other topologies are suitable for use by the invention as well (e.g., token ring, hub-and-spoke, etc.). 
     Furthermore, it should be understood that the data storage system  70 , as shown in FIG. 4, can be formed by a filesystem other than the UNIX filesystem and directory systems other than the LDAP directory system. For example, the data storage system  70  can use a Windows/NT filesystem rather than the UNIX filesystem. In such an arrangement, the procedures for responding to access requests (e.g., see FIGS. 6-12) can be configured to handle Windows/NT access operations when the identified portion of the data storage system is a Windows/NT file.