Veritas™ File System 5.0.1 Programmer's Reference Guide

feature only purges records that are older than a time specified by fcl_keeptime.
The freed space is always in units of an internal hole size.
Figure 2-2 displays the file system freeing up space in the FCL file in 8K units.
When the FCL file surpasses the maximum allocation for the first time and the
number of older records is 20K, the program purges 16K. This leaves a 16K hole
following the FCL superblock. The first valid offset in the FCL superblock is then
updated to 24K.
Figure 2-2
FCL record purging example
Superblock
Record
Record
Record
Offset 0x0
first offset = 8K
Superblock
Offset 0x0
first offset = 24KB
FCL Before: No holes
FCL After:
Record
Record
A 16 K hole exists at offset 8K
16K Hole
Record
Record
Record
Application programming interface for File Change
Log
In addition to the existing programmatic interface exposed through libvxfsutil:
vxfs_fcl_sync,VxFS 5.0 provides a new set of programmatic interfaces which
replace the mechanism to access an FCL file via the set of standard system calls:
open(2), lseek(2), read(2) and close(2). This API provides the following
improvements:
Ease of use
The API reduces the need to write additional code to parse FCL entries.
Most of the on-disk FCL records are of a fixed size and contain only the default
information such as the inode number or time-stamp. However, some records can
27File Change Log
Application programming interface for File Change Log