DISKLABEL(5) BSD Programmer's Manual DISKLABEL(5)NAMEdisklabel - disk pack label
SYNOPSIS
#include <sys/disklabel.h>
DESCRIPTION
Each disk or disk pack on a system may contain a disk label which pro-
vides detailed information about the geometry of the disk and the parti-
tions into which the disk is divided. It should be initialized when the
disk is formatted, and may be changed later with the disksetup(8) pro-
gram. This information is used by the system disk driver and by the
bootstrap program to determine how to program the drive and where to find
the filesystems on the disk partitions. Additional information is used
by the filesystem in order to use the disk most efficiently and to locate
important filesystem information. The description of each partition con-
tains an identifier for the partition type (standard filesystem, swap
area, etc.). The filesystem updates the in-core copy of the label if it
contains incomplete information about the filesystem.
The label is located in sector number LABELSECTOR of the drive, usually
sector 0 where it may be found without any information about the disk ge-
ometry. It is at an offset LABELOFFSET from the beginning of the sector,
to allow room for the initial bootstrap. The disk sector containing the
label is normally made read-only so that it is not accidentally overwrit-
ten by pack-to-pack copies or swap operations; the DIOCWLABEL ioctl(2),
which is done as needed by the disklabel program.
A copy of the in-core label for a disk can be obtained with the
DIOCGDINFO ioctl; this works with a file descriptor for a block or char-
acter (``raw'') device for any partition of the disk. The in-core copy
of the label is set by the DIOCSDINFO ioctl. The offset of a partition
cannot generally be changed while it is open, nor can it be made smaller
while it is open. One exception is that any change is allowed if no la-
bel was found on the disk, and the driver was able to construct only a
skeletal label without partition information. Finally, the DIOCWDINFO
ioctl operation sets the in-core label and then updates the on-disk la-
bel; there must be an existing label on the disk for this operation to
succeed. Thus, the initial label for a disk or disk pack must be in-
stalled by writing to the raw disk. All of these operations are normally
done using disklabel.
Please refer to <sys/disklabel.h> for the actual format of the disk la-
bel.
SEE ALSOdisktab(5), disksetup(8)HISTORY
The disklabel file format is currently under development.
BSDI BSD/OS January 8, 1998 1
