HP JFS 3.3 and HP OnLineJFS 3.3 VERITAS File System 3.3 System Administrator's Guide

114 Chapter6

Application Interface

Extent Information

The VX_SETEXT ioctl allows an application to reserve space for a ﬁle, and

set ﬁxed extent sizes and ﬁle allocation ﬂags. The current state of much

of this information can be obtained by applications using the VX_GETEXT

ioctl (the getext command provides access to this functionality). For

details, see getext(1M), setext(1M), and vxfsio(7).

NOTE The VX_SETEXT ioctl is available only with the HP OnLineJFS product.

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

vx_ext structure. When using VX_SETEXT, always use the following

procedure:

Step 1. Use VX_GETEXT to read the current settings.

Step 2. Modify the values to be changed.

Step 3. Call VX_SETEXT to set the values.

NOTE Follow this procedure carefully. Otherwise, a ﬁxed extent size could be

cleared when the reservation is changed.

Space Reservation

Storage can be reserved for a ﬁle at any time. When a VX_SETEXT ioctl is

issued, the reservation value is set in the inode on disk. If the ﬁle size is

less than the reservation amount, the kernel allocates space to the ﬁle

from the current ﬁle size up to the reservation amount. When the ﬁle is

truncated, space below the reserved amount is not freed. The VX_TRIM,

VX_NOEXTEND, VX_CHGSIZE, VX_NORESERVE and VX_CONTIGUOUS ﬂags can

be used to modify reservation requests.

NOTE VX_NOEXTEND is the only one of these ﬂags that is persistent; the other

ﬂags may have persistent effects, but they are not returned by the