Veritas™ File System 5.0.1 Programmer's Reference Guide

the current size of the file and the size after the operation succeeds). VX_GROWFILE

has persistent effects, but is not visible as an allocation flag. This flag is visible

through the VX_GETEXT ioctl.

Allocation flags with fixed extent size

The VX_ALIGN flag can be used to specify an allocation flag for fixed extent size.

This flag has no effect if it is specified with a reservation request. The VX_ALIGN

flag specifies the alignment requirement for allocating future extents that are

aligned on a fixed extent size boundary relative to the start of the allocation unit.

This flag can be used to align extents to disk striping boundaries or physical disk

boundaries. The VX_ALIGN flag is persistent and the VX_GETEXT ioctl returns the

flag.

How to use extent attribute APIs

First, verify that the target file system is VxFS, and then determine the file system

block size using the statfs() call. The type for VxFS is MNT_VXFS on most platforms,

and the file system block size is returned in statfs.f_bsize. The block size must be

known for setting or interpreting the extent attribute information through VxFS

extent attribute APIs.

Each invocation of the VX_SETEXT ioctl affects all the elements in the vx_ext

structure.

To use VX_SETEXT

Call the VX_GETEXT ioctl to read the current settings, if any.

Modify the current values to be changed.

Call the VX_SETEXT ioctl to set the new values.

Warning: Follow this procedure carefully. A fixed extent size may be inadvertently

cleared when the reservation is changed. When copying files between VxFS and

non-VxFS file systems, the extent attributes cannot be preserved. The attribute

values returned for a file in a vx_ext structure have a different effect on another

VxFS file system with a different file system block size from the source file system.

Translation of attribute values for different block sizes may be necessary when

copying files with attributes between two file systems of a different block size.

83Veritas File System I/O

Extents