As mentioned above, the file system defines three types of volumes:
• Local disk volumes
• Remote volumes
• Memory-resident volumes.
Local disk volumes are volumes directly attached to the PenPoint computer.
Remote volumes are those that are connected through a network or channel controller. Memory resident volumes reside in PenPoint computer RAM.
1ll. L 1.3
CHAPTER 70 / File System Principles and Organization 51 Volumes
Local Disk Volumes 70.1.2.1
Local disk volumes exist on hard or floppy disk drives internal to or attached to the PenPoint computer. The user can connect and disconnect external disks at any time.
PenPoint has no native disk format. Rather, the file system makes use of a volume's normal organization to store additional information. Currently PenPoint uses the MS-DOS FAT disk format.
An MS-DOS volume name is a string containing between 1 and 11 characters.
The volume name cannot use the following characters:
/\;:=<>[]
The name can use spaces, but not tabs.
Here are some examples of MS-DOS volume names:
.A
• MYDISK
• RAM
• MYVOLUME
• BACKUP 3
• ACCNTS RCVL.
The MS-DOS disk format consists of files and directories. In MS-DOS, file names are limited to 8 characters with a 3-character file extension, there are only a few file attri-butes, and there is only one type offile (data). PenPoint uses MS-DOS format files and directories whenever possible to store its own files and directories. However, when a file or directory has one or more of these characteristics:
• A node name that uses any control characters, lowercase characters, or any of these special characters:
*
? / \ I . , ; : + = < > [ ] " (space).• A name longer than eight characters, plus a three-character extension.
• A name that uses lower case characters.
• Has client-defined attributes.
PenPoint creates a special file, named PENPOINT.DIR, in that file or directory's parent directory, which contains the additional information. The PENPOINT.DIR file is described in further detail in Chapter 71, Accessing the File System.
In the future, PenPoint may support disk formats other than the MS-DOS FAT format. The file system architecture makes it easy for GO or third parties to develop support for other disk formats.
Remote Volumes
Remote volumes are available over a network or a communication channel. The name for a remote volume is limited only by the network's volume naming conventions.
70.1.2.2
52 PEN POINT ARCHITECTURAL REFERENCE Part 7 / File System
A computer that responds to a remote file access protocol is called a remote file server. A remote file server can be any sort of computer, ranging from a personal computer to a dedicated file server with gigabytes of storage. The administrator of the remote file server decides how much of the file system to make available to the PenPoint computer and what sort of security to enforce.
As with local disk volumes, the file system provides features that might exceed the remote file system's capabilities. PenPoint supports these extended features in a fashion similar to that for local disk volumes.
To access a remote volume, file system operations must use the remote file access protocol that is appropriate to the server. For example, a TOPS remote volume requires a TOPS remote file access protocol. Like file system support for local disk volumes, the file system architecture makes it easy for GO or third parties to develop support for other protocols.
Memory-Resident Volumes
Memory-resident volumes reside in the PenPoint computer's RAM. The memory-resident RAM volume is named RAM. This volume is only available with the SDK version of Pen Point 1.0, and only when the ENVIRON.INI file includes the Config=DebugRAM directive. There is only one RAM volume, and PenPoint dynamically allocates RAM memory to the RAM volume as needed.
Nodes
Within each volume, the file system maintains a tree of file system nodes. There are two types of nodes:
• Directory nodes
• File nodes.
Directories are catalogs of files and directories. Directories can contain both files and other directories. As in MS-DOS, a volume is organized into a strictly hierarchical structure of files and directories. Strictly hierarchical means that each node appears in only one directory; there are no multiple references to nodes.
The top-most node in a volume's directory structure is the root directory. All other nodes in the volume are descendants of the root directory. Because a volume is self-contained, the directories within a given volume contain nodes only in that volume.
Figure 70-1 illustrates an example of the file system on a volume.
CHAPTER 70 / File System Principles and Organization 53
file file file
file
The name of a node is a string containing 1 to 31 characters. Any character is valid except backs lash (\) and null (character code 0), and a node name is not valid if it begins or ends with a space character. Here are some examples of valid node names:
• Red
• GO Corporation
• A Very, Very, Lengthy Node Name
• Patient X: Cardiac Status
• FILENAME.DOS.
Note that the characters can be uppercase or lowercase. The file system stores the node names in upper and lower case, but ignores the case when it performs compansons.
Your application can use the FSNameValid function to determine if a user-supplied file name is a valid node name.
All of the node names within a single directory are unique; the file system will reject any request to create a duplicate node name. You can use the
fsExistGenUnique or fsNoExistCreateUnique flags, discussed in Chapter, 72,
Nodes
54 PENPOINT ARCHITECTURAL REFERENCE Part 7 I File System
Using the File System, to direct the file system to generate a unique node name when it creates a new node .
. Directories and Directory Entries
A directory is a container for file system nodes; it contains a directory entry for each node directly subordinate to it. Each directory entry contains the file-system and client-defined attributes for the node it describes.
Figure 70-2 shows the contents of one of the directory entries shown in Figure 70-1.
PENPOINT.DIR file File Entry
File Entry