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Extract from Internet Encyclopedia
The Network File System (NFS), developed by SunMicrosystems, is the de facto standard for file sharing among Unix hosts. NFS Version 3 is documented in RFC1813. The Mount Protocol is closely related. NFS is implemented using the RPC Protocol, designed to support remote procedure calls. All NFS operations are implemented as RPC procedures.
A summary of NFS procedures:
Procedure 0: NULL - Do nothing
Procedure 1: GETATTR - Get file attributes
Procedure 2: SETATTR - Set file attributes
Procedure 3: LOOKUP - Lookup filename
Procedure 4: ACCESS - Check Access Permission
Procedure 5: READLINK - Read from symbolic link
Procedure 6: READ - Read From file
Procedure 7: WRITE - Write to file
Procedure 8: CREATE - Create a file
Procedure 9: MKDIR - Create a directory
Procedure 10: SYMLINK - Create a symbolic link
Procedure 11: MKNOD - Create a special device
Procedure 12: REMOVE - Remove a File
Procedure 13: RMDIR - Remove a Directory
Procedure 14: RENAME - Rename a File or Directory
Procedure 15: LINK - Create Link to an object
Procedure 16: READDIR - Read From Directory
Procedure 17: READDIRPLUS - Extended read from directory
Procedure 18: FSSTAT - Get dynamic file system information
Procedure 19: FSINFO - Get static file system Information
Procedure 20: PATHCONF - Retrieve POSIX information
Procedure 21: COMMIT - Commit cached data on a server to
stable storage
NFS is a stateless protocol. This means that the file server stores no per-client information, and there are no NFS "connections". For example, NFS has no operation to open a file, since this would require the server to store state information (that a file is open; what its file descriptor is; the next byte to read; etc). Instead, NFS supports a Lookup procedure, which converts a filename into a file handle. This file handle is an unique, immutable identifier, usually an i-node number, or disk block address. NFS does have a Read procedure, but the client must specify a file handle and starting offset for every call to Read. Two identical calls to Read will yield the exact same results. If the client wants to read further in the file, it must call Read with a larger offset.
Of course, this is seldom seen by the end user. Most operating systems provide system calls to open files, and read from them sequentially. The client's operating system must maintain the required state information, and translate system calls into stateless NFS operations.
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Last modified: 08/May/98 (11:53)