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DISKLABEL64(5)           DragonFly File Formats Manual          DISKLABEL64(5)


NAME

     disklabel64 -- 64 bit disk pack label


SYNOPSIS

     #include <sys/disklabel64.h>


DESCRIPTION

     Each disk or disk pack on a system may contain a 64 bit disk label which
     provides detailed information 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 disklabel64(8) program.  This
     information is used by the system disk driver to determine how to program
     the drive.  Additional information is used by the file system in order 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 byte number 0 where it may be found without any
     information about the disk geometry.  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 disklabel64(8) program.

     A copy of the in-core label for a disk can be obtained with the
     DIOCGDINFO64 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 DIOCSDINFO64 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 DIOCWDINFO64 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 disklabel64(8).

     The format of the 64 bit disk label is specified in <sys/disklabel64.h>.


SEE ALSO

     disklabel32(5), disktab(5), disklabel64(8)

DragonFly 4.3                   August 21, 2008                  DragonFly 4.3

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