Veritas™ File System 5.0.1 Programmer's Reference Guide

See the fcladm(1M) manual page.
When FCL loggin is activated, new FCL records are appended to the FCL file as
file system changes occur. When FCL logging is turned off, further recording
stops, but the FCL file remains as /lost+found/changelog. You can only remove
an FCL file by using the fcladm command.
The FCL file has an associated version that represents the layout or is the internal
representation of the FCL file, along with the list of events recorded in the FCL
file.
Whenever a new version of VxFS is released, the following occurs:
■ There may either be additional events recorded in the FCL file
■ The internal representation of the FCL file may change
This results in the FCL file version getting updated. For example, in VxFS 4.1, the
default was Version 3. However, because Vxfs 5.0 records additional sets of events
that are not available in Version 3 (such as file opens), the default version in VxFS
5.0 is 4. To provide backward compatibility for applications developed on VxFS
4.1, VxFS 5.0 and later provide an option to specify an FCL version during
activation. Depending on the specified version, the logging of the new record types
is either allowed or disallowed.
The logging of most of the newly added records in VxFS 5.0, such as file opens
and I/O statistics, is optional and is turned off by default. Recording of these
events can be enabled or disabled using the [set] and [clear] options of the fcladm
command.
The FCL meta-information comprising of the file system state, version, and the
set of events being tracked is persistent across reboots and file system unmounts
or mounts. The version and event information is also persistent across
re-activations of FCL logging.
File Change Log file layout
In VxFS 4.1, the internal layout of the FCL file was exposed to the user and the
applications were expected to access the FCL file using standard file system
interfaces, such as open(2), read(2), and lseek(2). However, this methodology may
lead to future compatibility issues, because if the underlying FCL layout and the
FCL version changes, the application must be changed and recompiled to
accommodate these changes.
VxFS 5.0 introduces a new programming interface, which provides improved
compatibility, even when the on-disk FCL layout changes. With this API, the FCL
layout is not a concern for applications. Consequently, this section provides only
a rudimentary description of the FCL layout.
File Change Log
About the File Change Log file
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