Veritas™ File System 5.0.1 Programmer's Reference Guide

Figure 4-1

Alternate Namespace

file1

Alternate namespace

for named data

streams

data_stream_1

data_stream_2

The file1 file has two named data streams: data_stream_1 and data_stream_2.

Every file can have its own alternate namespace to store named data streams. The

alternate namespace can be accessed through the named data stream APIs

supported by VxFS.

Access to the named data stream can be done through a file descriptor using the

named data stream library functions. Applications can open the named data

stream to obtain a file descriptor and perform read(), write(), and mmap() operations

using the file descriptor. These system calls work as though they are operating

on a regular file. The named data streams of a file are stored in a hidden named

data stream directory inode associated with the file. The hidden directory inode

for the file can be accessed only through the named data stream application

programming interface.

There are no VxFS-supplied administrative commands to use this feature. A VxFS

API is provided for creating, reading, and writing the named data streams of a

file.

Uses for named data streams

Named data streams allow applications to attach information to a file that appears

to be hidden. An administrative program could use this to attach file usage

information, backup information, and so on. An application could use this feature

to hide or collect file attachments. For example, a multi-media document could

have all text, audio clips, and video clips organized in one file rather than in several

files. A document being reviewed by multiple people could have each person’s

comments attached to the file as a named data stream.

Named data streams application programming

interface

The following standard system calls can manipulate named data streams:

Named data streams

Uses for named data streams