DISKLABEL(5) MachTen Programmer’s Manual DISKLABEL(5)

NAME
disklabel - 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 geome-
try of the disk and the partitions into which the disk is
divided. It should be initialized when the disk is for-
matted, and may be changed later with the disklabel(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 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 descrip-
tion of each partition contains an identifier for the par-
tition 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 geometry. It is at an offset
LABELOFFSET from the beginning of the sector, to allow
room for the initial bootstrap. The disk sector contain-
ing 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, which is done as needed
by the disklabel(8) program.

A copy of the in-core label for a disk can be obtained
with the DIOCGDINFO ioctl; this works with a file descrip-
tor for a block or character (‘‘raw’’) device for any par-
tition 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 label 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 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 disklabel(8).

The format of the disk label, as specified in
<sys/disklabel.h>, is
/*
* Disk description table, see disktab(5)
*/
#define DISKTAB "/etc/disktab"

/*
* Each disk has a label which includes information about the hardware
* disk geometry, filesystem partitions, and drive specific information.
* The label is in block 0 or 1, possibly offset from the beginning
* to leave room for a bootstrap, etc.
*/
#define LABELSECTOR 0 /* sector containing label */
#define LABELOFFSET 64 /* offset of label in sector */
#define DISKMAGIC ((u_long) 0x82564557) /* The disk magic number */
#ifndef MAXPARTITIONS
#define MAXPARTITIONS 8
#endif

#ifndef LOCORE
struct disklabel {
u_long d_magic; /* the magic number */
short d_type; /* drive type */
short d_subtype; /* controller/d_type specific */
char d_typename[16]; /* type name, e.g. "eagle" */
/*
* d_packname contains the pack identifier and is returned when
* the disklabel is read off the disk or in-core copy.
* d_boot0 and d_boot1 are the (optional) names of the
* primary (block 0) and secondary (block 1-15) bootstraps
* as found in /usr/mdec. These are returned when using
* getdiskbyname(3) to retrieve the values from /etc/disktab.
*/
#if defined(KERNEL) || defined(STANDALONE)
char d_packname[16]; /* pack identifier */
#else
union {
char un_d_packname[16]; /* pack identifier */
struct {
char *un_d_boot0; /* primary bootstrap name */
char *un_d_boot1; /* secondary bootstrap name */
} un_b;
} d_un;
#define d_packname d_un.un_d_packname
#define d_boot0 d_un.un_b.un_d_boot0
#define d_boot1 d_un.un_b.un_d_boot1
#endif /* ! KERNEL or STANDALONE */
/* disk geometry: */
u_long d_secsize; /* # of bytes per sector */
u_long d_nsectors; /* # of data sectors per track */
u_long d_ntracks; /* # of tracks per cylinder */
u_long d_ncylinders; /* # of data cylinders per unit */
u_long d_secpercyl; /* # of data sectors per cylinder */
u_long d_secperunit; /* # of data sectors per unit */
/*
* Spares (bad sector replacements) below
* are not counted in d_nsectors or d_secpercyl.
* Spare sectors are assumed to be physical sectors
* which occupy space at the end of each track and/or cylinder.
*/
u_short d_sparespertrack; /* # of spare sectors per track */
u_short d_sparespercyl; /* # of spare sectors per cylinder */
/*
* Alternate cylinders include maintenance, replacement,
* configuration description areas, etc.
*/
u_long d_acylinders; /* # of alt. cylinders per unit */

/* hardware characteristics: */
/*
* d_interleave, d_trackskew and d_cylskew describe perturbations
* in the media format used to compensate for a slow controller.
* Interleave is physical sector interleave, set up by the formatter
* or controller when formatting. When interleaving is in use,
* logically adjacent sectors are not physically contiguous,
* but instead are separated by some number of sectors.
* It is specified as the ratio of physical sectors traversed
* per logical sector. Thus an interleave of 1:1 implies contiguous
* layout, while 2:1 implies that logical sector 0 is separated
* by one sector from logical sector 1.
* d_trackskew is the offset of sector 0 on track N
* relative to sector 0 on track N-1 on the same cylinder.
* Finally, d_cylskew is the offset of sector 0 on cylinder N
* relative to sector 0 on cylinder N-1.
*/
u_short d_rpm; /* rotational speed */
u_short d_interleave; /* hardware sector interleave */
u_short d_trackskew; /* sector 0 skew, per track */
u_short d_cylskew; /* sector 0 skew, per cylinder */
u_long d_headswitch; /* head switch time, usec */
u_long d_trkseek; /* track-to-track seek, usec */
u_long d_flags; /* generic flags */
#define NDDATA 5
u_long d_drivedata[NDDATA]; /* drive-type specific information */
#define NSPARE 5
u_long d_spare[NSPARE]; /* reserved for future use */
u_long d_magic2; /* the magic number (again) */
u_short d_checksum; /* xor of data incl. partitions */

/* filesystem and partition information: */
u_short d_npartitions; /* number of partitions in following */
u_long d_bbsize; /* size of boot area at sn0, bytes */
u_long d_sbsize; /* max size of fs superblock, bytes */
struct partition { /* the partition table */
u_long p_size; /* number of sectors in partition */
u_long p_offset; /* starting sector */
u_long p_fsize; /* filesystem basic fragment size */
u_char p_fstype; /* filesystem type, see below */
u_char p_frag; /* filesystem fragments per block */
u_short p_cpg; /* filesystem cylinders per group */
} d_partitions[MAXPARTITIONS]; /* actually may be more */
};

/* d_type values: */
#define DTYPE_SMD 1 /* SMD, XSMD; VAX hp/up */
#define DTYPE_MSCP 2 /* MSCP */
#define DTYPE_DEC 3 /* other DEC (rk, rl) */
#define DTYPE_SCSI 4 /* SCSI */
#define DTYPE_ESDI 5 /* ESDI interface */
#define DTYPE_ST506 6 /* ST506 etc. */
#define DTYPE_FLOPPY 10 /* floppy */

#ifdef DKTYPENAMES
static char *dktypenames[] = {
"unknown",
"SMD",
"MSCP",
"old DEC",
"SCSI",
"ESDI",
"type 6",
"type 7",
"type 8",
"type 9",
"floppy",
0
};
#define DKMAXTYPES (sizeof(dktypenames) / sizeof(dktypenames[0]) - 1)
#endif

/*
* Filesystem type and version.
* Used to interpret other filesystem-specific
* per-partition information.
*/
#define FS_UNUSED 0 /* unused */
#define FS_SWAP 1 /* swap */
#define FS_V6 2 /* Sixth Edition */
#define FS_V7 3 /* Seventh Edition */
#define FS_SYSV 4 /* System V */
#define FS_V71K 5 /* V7 with 1K blocks (4.1, 2.9) */
#define FS_V8 6 /* Eighth Edition, 4K blocks */
#define FS_BSDFFS 7 /* 4.2BSD fast file system */

#ifdef DKTYPENAMES
static char *fstypenames[] = {
"unused",
"swap",
"Version 6",
"Version 7",
"System V",
"4.1BSD",
"Eighth Edition",
"4.2BSD",
0
};
#define FSMAXTYPES (sizeof(fstypenames) / sizeof(fstypenames[0]) - 1)
#endif

/*
* flags shared by various drives:
*/
#define D_REMOVABLE 0x01 /* removable media */
#define D_ECC 0x02 /* supports ECC */
#define D_BADSECT 0x04 /* supports bad sector forw. */
#define D_RAMDISK 0x08 /* disk emulator */
#define D_CHAIN 0x10 /* can do back-back transfers */

/*
* Drive data for SMD.
*/
#define d_smdflags d_drivedata[0]
#define D_SSE 0x1 /* supports skip sectoring */
#define d_mindist d_drivedata[1]
#define d_maxdist d_drivedata[2]
#define d_sdist d_drivedata[3]

/*
* Drive data for ST506.
*/
#define d_precompcyl d_drivedata[0]
#define d_gap3 d_drivedata[1] /* used only when formatting */

#ifndef LOCORE
/*
* Structure used to perform a format
* or other raw operation, returning data
* and/or register values.
* Register identification and format
* are device- and driver-dependent.
*/
struct format_op {
char *df_buf;
int df_count; /* value-result */
daddr_t df_startblk;
int df_reg[8]; /* result */
};

/*
* Structure used internally to retrieve
* information about a partition on a disk.
*/
struct partinfo {
struct disklabel *disklab;
struct partition *part;
};

/*
* Disk-specific ioctls.
*/
/* get and set disklabel; DIOCGPART used internally */
#define DIOCGDINFO _IOR(’d’, 101, struct disklabel) /* get */
#define DIOCSDINFO _IOW(’d’, 102, struct disklabel) /* set */
#define DIOCWDINFO _IOW(’d’, 103, struct disklabel) /* set, update disk */
#define DIOCGPART _IOW(’d’, 104, struct partinfo) /* get partition */

/* do format operation, read or write */
#define DIOCRFORMAT _IOWR(’d’, 105, struct format_op)
#define DIOCWFORMAT _IOWR(’d’, 106, struct format_op)

#define DIOCSSTEP _IOW(’d’, 107, int) /* set step rate */
#define DIOCSRETRIES _IOW(’d’, 108, int) /* set # of retries */
#define DIOCWLABEL _IOW(’d’, 109, int) /* write en/disable label */

#define DIOCSBAD _IOW(’d’, 110, struct dkbad) /* set kernel dkbad */

#endif LOCORE