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

Chapter 6 115
Application Interface
Extent Information
VX_GETEXT ioctl.
If the VX_TRIM flag is set, when the last close occurs on the inode, the
reservation is trimmed to match the file size and the VX_TRIM flag is
cleared. Any unused space is freed. This can be useful if an application
needs enough space for a file, but it is not known how large the file will
become. Enough space can be reserved to hold the largest expected file,
and when the file has been written and closed, any extra space will be
released.
If the VX_NOEXTEND flag is set, an attempt to write beyond the current
reservation, which requires the allocation of new space for the file, fails
instead. To allocate new space to the file, the space reservation must be
increased. This can be used like ulimit to prevent a file from using too
much space.
If the VX_CONTIGUOUS flag is set, any space allocated to satisfy the
current reservation request is allocated in one extent. If there is not one
extent large enough to satisfy the request, the request fails. For example,
if a file is createdand a 1 MB contiguous reservation is requested, the file
size is set to zero and the reservation to 1 MB. The file will have one
extent that is 1 MB long. If another reservation request is made for a 3
MB contiguous reservation, the new request will find that the first 1 MB
is already allocated and allocate a 2 MB extent to satisfy the request. If
there are no 2 MB extents available, the request fails. (Extents are, by
definition, contiguous.)
NOTE Because VX_CONTIGUOUS is not a persistent flag, space will not be
allocated contiguously after doing a file system restore.
If the VX_NORESERVE flag is set, the reservation value in the inode is not
changed. This flag is used by applications to do temporary reservation.
Any space past the end of the file is given up when the file is closed. For
example, if the cp command is copying a file that is 1 MB long, it can
request a 1 MB reservation with the VX_NORESERVE flag set. The space is
allocated, but the reservation in the file is left at 0. If the program aborts
for any reason or the system crashes, the unused space past the end of
the file is released. When the program finishes, there is no cleanup
because the reservation was never recorded on disk.
If the VX_CHGSIZE flag is set, the file size is increased to match the