NAME
disklabel32 —
32 bit disk pack label
SYNOPSIS
#include
<sys/disklabel.h>
DESCRIPTION
Each disk or disk pack on a system may contain a disk label which provides detailed information about the geometry of the disk and the partitions into which the disk is divided. It should be initialized when the disk is formatted, and may be changed later with the disklabel32(8) program. 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 file systems on the disk partitions. Additional information is used by the file system in order to use the disk most efficiently and to locate important file system information. The description of each partition contains an identifier for the partition type (standard file system, swap area, etc.). The file system updates the in-core copy of the label if it contains incomplete information about the file system.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 geometry. 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 overwritten
by pack-to-pack copies or swap operations; the
DIOCWLABEL
ioctl(2), which is done as needed by the
disklabel32(8) program.
A copy of the in-core label for a disk can be obtained with the
DIOCGDINFO
ioctl(2); this works with a file descriptor for a block or character
(``raw'') device for any partition of the disk. The in-core copy of the
label is set by the DIOCSDINFO
ioctl(2). 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 label was found on the disk, and the driver
was able to construct only a skeletal label without partition information.
Finally, the DIOCWDINFO
ioctl(2) operation sets the in-core label and then updates the
on-disk label; 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 installed by writing to the raw disk. All of these operations are
normally done using
disklabel32(8).
The format of the disk label is specified in
<sys/disklabel32.h>.