VERITAS File System 4.1 Administrator's Guide

Application Interface
Extent Information
Chapter 4 81
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 created and 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 reservation amount. This
flag can be used to create files with uninitialized data. Because this allows uninitialized data
in files, it is restricted to users with appropriate privileges.
It is possible to use these flags in combination. For example, using VX_CHGSIZE and
VX_NORESERVE changes the file size but does not set any reservation. When the file is
truncated, the space is freed. If the VX_NORESERVE flag had not been used, the reservation
would have been set on disk along with the file size.