Veritas™ File System 5.0.1 Programmer's Reference Guide

be of variable sizes, such as a file remove or rename record. These records contain

additional information, such as the name of a file that is removed or renamed.

To ensure that the first few bytes at the start of any file system block is always a

valid FCL record (if the filename crosses a block boundary), the file system block

may be split across multiple on-disk records. Previously, you were required to

write additional code to assemble these records to get the filename. The VxFS 5.0

API provides a mechanism to directly read a single assembled logical record. This

makes it easier for applications using the API. The API also lets the application

specify a filter to indicate a subset of the events of interest and return only required

records.

Backward compatibility

The API lets applications read the FCL independent of the FCL layout changes.

For example, consider a scenario where an application directly accesses and

interprets the on-disk FCL records. If the next VxFS release adds new records or

changes the way the records are stored in the FCL file, the application needs to

be rewritten or at least re-compiled to accommodate for the changes (under

previous VxFS versions).

With an intermediate API, the on-disk layout of FCL is hidden from the application,

so even if the disk layout of FCL changes, the API internally translates the data

returns the expected output record to the user. The user application can then

continue without a recompilation or a rewrite.This insulates programs from FCL

layout changes and provides greater compatibility for existing applications.

API functions

The API uses the following type of functions:

■ Functions for accessing FCL records

■ Functions for seeking offsets and time stamps

Functions for accessing File Change Log records

The following are general functions for accessing FCL records:

Opens the FCL file and returns a handle which can be used for

further operations. All subsequent accesses of the FCL file through

the API must use this handle.

vxfs_fcl_open

Closes the FCL file and cleans up resources associated with the

handle

vxfs_fcl_close

File Change Log

Application programming interface for File Change Log