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 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 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 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 disklabel(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 disklabel(8).

The format of the disk label, as specified in <sys/disklabel.h>, is

    #ifndef _SYS_DISKLABEL_H_
    #define	_SYS_DISKLABEL_H_
    #ifndef _KERNEL
    #include <sys/types.h>
    #endif
    #include <sys/ioccom.h>
    /*
     * Disk description table, see disktab(5)
     */
    #define	_PATH_DISKTAB	"/etc/disktab"
    #define	DISKTAB		"/etc/disktab"		/* deprecated */
    /*
     * Each disk has a label which includes information about the hardware
     * disk geometry, file system 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.
     */
    /* XXX these should be defined per controller (or drive) elsewhere, not here! */
    #ifdef __i386__
    #define LABELSECTOR	1			/* sector containing label */
    #define LABELOFFSET	0			/* offset of label in sector */
    #endif
    #ifdef __alpha__
    #define LABELSECTOR	0
    #define LABELOFFSET	64
    #endif
    #ifndef	LABELSECTOR
    #define LABELSECTOR	0			/* sector containing label */
    #endif
    #ifndef	LABELOFFSET
    #define LABELOFFSET	64			/* offset of label in sector */
    #endif
    #define DISKMAGIC	((u_int32_t)0x82564557)	/* The disk magic number */
    #ifndef MAXPARTITIONS
    #define	MAXPARTITIONS	8
    #endif
    #define	LABEL_PART	2		/* partition containing label */
    #define	RAW_PART	2		/* partition containing whole disk */
    #define	SWAP_PART	1		/* partition normally containing swap */
    #ifndef LOCORE
    struct disklabel {
    	u_int32_t d_magic;		/* the magic number */
    	u_int16_t d_type;		/* drive type */
    	u_int16_t d_subtype;		/* controller/d_type specific */
    	char	  d_typename[16];	/* type name, e.g. "eagle" */
    	char	  d_packname[16];	/* pack identifier */
    			/* disk geometry: */
    	u_int32_t d_secsize;		/* # of bytes per sector */
    	u_int32_t d_nsectors;		/* # of data sectors per track */
    	u_int32_t d_ntracks;		/* # of tracks per cylinder */
    	u_int32_t d_ncylinders;		/* # of data cylinders per unit */
    	u_int32_t d_secpercyl;		/* # of data sectors per cylinder */
    	u_int32_t 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_int16_t d_sparespertrack;	/* # of spare sectors per track */
    	u_int16_t d_sparespercyl;	/* # of spare sectors per cylinder */
    	/*
    	 * Alternate cylinders include maintenance, replacement, configuration
    	 * description areas, etc.
    	 */
    	u_int32_t 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_int16_t d_rpm;		/* rotational speed */
    	u_int16_t d_interleave;		/* hardware sector interleave */
    	u_int16_t d_trackskew;		/* sector 0 skew, per track */
    	u_int16_t d_cylskew;		/* sector 0 skew, per cylinder */
    	u_int32_t d_headswitch;		/* head switch time, usec */
    	u_int32_t d_trkseek;		/* track-to-track seek, usec */
    	u_int32_t d_flags;		/* generic flags */
    #define NDDATA 5
    	u_int32_t d_drivedata[NDDATA];	/* drive-type specific information */
    #define NSPARE 5
    	u_int32_t d_spare[NSPARE];	/* reserved for future use */
    	u_int32_t d_magic2;		/* the magic number (again) */
    	u_int16_t d_checksum;		/* xor of data incl. partitions */
    			/* file system and partition information: */
    	u_int16_t d_npartitions;	/* number of partitions in following */
    	u_int32_t d_bbsize;		/* size of boot area at sn0, bytes */
    	u_int32_t d_sbsize;		/* max size of fs superblock, bytes */
    	struct	partition {		/* the partition table */
    		u_int32_t p_size;	/* number of sectors in partition */
    		u_int32_t p_offset;	/* starting sector */
    		u_int32_t p_fsize;	/* file system basic fragment size */
    		u_int8_t p_fstype;	/* file system type, see below */
    		u_int8_t p_frag;	/* file system fragments per block */
    		union {
    			u_int16_t cpg;	/* UFS: FS cylinders per group */
    			u_int16_t sgs;	/* LFS: FS segment shift */
    		} __partition_u1;
    #define	p_cpg	__partition_u1.cpg
    #define	p_sgs	__partition_u1.sgs
    	} d_partitions[MAXPARTITIONS];	/* actually may be more */
    };
    #else /* LOCORE */
    	/*
    	 * offsets for asm boot files.
    	 */
    	.set	d_secsize,40
    	.set	d_nsectors,44
    	.set	d_ntracks,48
    	.set	d_ncylinders,52
    	.set	d_secpercyl,56
    	.set	d_secperunit,60
    	.set	d_end_,276		/* size of disk label */
    #endif /* LOCORE */
    /* 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_HPIB		7		/* CS/80 on HP-IB */
    #define	DTYPE_HPFL		8		/* HP Fiber-link */
    #define	DTYPE_FLOPPY		10		/* floppy */
    #define	DTYPE_CCD		11		/* concatenated disk */
    #define	DTYPE_VINUM		12		/* vinum volume */
    #define	DTYPE_DOC2K		13		/* Msys DiskOnChip */
    #if defined(PC98) && !defined(PC98_ATCOMPAT)
    #define	DSTYPE_SEC256		0x80		/* physical sector size=256 */
    #endif
    #ifdef DKTYPENAMES
    static char *dktypenames[] = {
    	"unknown",
    	"SMD",
    	"MSCP",
    	"old DEC",
    	"SCSI",
    	"ESDI",
    	"ST506",
    	"HP-IB",
    	"HP-FL",
    	"type 9",
    	"floppy",
    	"CCD",
    	"Vinum",
    	"DOC2K",
    	NULL
    };
    #define DKMAXTYPES	(sizeof(dktypenames) / sizeof(dktypenames[0]) - 1)
    #endif
    /*
     * File system type and version.
     * Used to interpret other file system-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 */
    #define	FS_MSDOS	8		/* MSDOS file system */
    #define	FS_BSDLFS	9		/* 4.4BSD log-structured file system */
    #define	FS_OTHER	10		/* in use, but unknown/unsupported */
    #define	FS_HPFS		11		/* OS/2 high-performance file system */
    #define	FS_ISO9660	12		/* ISO 9660, normally CD-ROM */
    #define	FS_BOOT		13		/* partition contains bootstrap */
    #define	FS_VINUM	14		/* Vinum drive */
    #ifdef	DKTYPENAMES
    static char *fstypenames[] = {
    	"unused",
    	"swap",
    	"Version 6",
    	"Version 7",
    	"System V",
    	"4.1BSD",
    	"Eighth Edition",
    	"4.2BSD",
    	"MSDOS",
    	"4.4LFS",
    	"unknown",
    	"HPFS",
    	"ISO9660",
    	"boot",
    	"vinum",
    	NULL
    };
    #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 */
    /*
     * Drive data for SCSI.
     */
    #define	d_blind		d_drivedata[0]
    #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;
    };
    /* DOS partition table -- located in boot block */
    #if defined(PC98) && !defined(PC98_ATCOMPAT)
    #define	DOSBBSECTOR	0	/* DOS boot block relative sector number */
    #define DOSLABELSECTOR	1	/* 0: 256b/s, 1: 512b/s */
    #define	DOSPARTOFF	0
    #define NDOSPART	16
    #define	DOSPTYP_386BSD	0x94	/* 386BSD partition type */
    #define	MBR_PTYPE_FreeBSD 0x94	/* FreeBSD partition type */
    struct dos_partition {
        	unsigned char	dp_mid;
    #define DOSMID_386BSD		(0x14|0x80) /* 386bsd|bootable */
    	unsigned char	dp_sid;
    #define DOSSID_386BSD		(0x44|0x80) /* 386bsd|active */
    	unsigned char	dp_dum1;
    	unsigned char	dp_dum2;
    	unsigned char	dp_ipl_sct;
    	unsigned char	dp_ipl_head;
    	unsigned short	dp_ipl_cyl;
    	unsigned char	dp_ssect;	/* starting sector */
    	unsigned char	dp_shd;		/* starting head */
    	unsigned short	dp_scyl;	/* starting cylinder */
    	unsigned char	dp_esect;	/* end sector */
    	unsigned char	dp_ehd;		/* end head */
    	unsigned short	dp_ecyl;	/* end cylinder */
    	unsigned char	dp_name[16];
    };
    #else /* IBMPC */
    #define DOSBBSECTOR	0	/* DOS boot block relative sector number */
    #define DOSPARTOFF	446
    #define NDOSPART	4
    #define	DOSPTYP_386BSD	0xa5	/* 386BSD partition type */
    struct dos_partition {
    	unsigned char	dp_flag;	/* bootstrap flags */
    	unsigned char	dp_shd;		/* starting head */
    	unsigned char	dp_ssect;	/* starting sector */
    	unsigned char	dp_scyl;	/* starting cylinder */
    	unsigned char	dp_typ;		/* partition type */
    	unsigned char	dp_ehd;		/* end head */
    	unsigned char	dp_esect;	/* end sector */
    	unsigned char	dp_ecyl;	/* end cylinder */
    	u_int32_t	dp_start;	/* absolute starting sector number */
    	u_int32_t	dp_size;	/* partition size in sectors */
    };
    #endif
    #define DPSECT(s) ((s) & 0x3f)		/* isolate relevant bits of sector */
    #define DPCYL(c, s) ((c) + (((s) & 0xc0)<<2)) /* and those that are cylinder */
    /*
     * 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 */
    #define DIOCWLABEL	_IOW('d', 109, int)	/* write en/disable label */
    #ifdef _KERNEL
    /*
     * XXX encoding of disk minor numbers, should be elsewhere.
     *
     * See <sys/reboot.h> for a possibly better encoding.
     *
     * "cpio -H newc" can be used to back up device files with large minor
     * numbers (but not ones >= 2^31).  Old cpio formats and all tar formats
     * don't have enough bits, and cpio and tar don't notice the lossage.
     * There are also some sign extension bugs.
     */
    /*
           3                   2                   1                   0
         1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
        _________________________________________________________________
        | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
        -----------------------------------------------------------------
        |    TYPE     |UNIT_2 | SLICE   |  MAJOR?       |  UNIT   |PART |
        -----------------------------------------------------------------
    */
    #define	dkmakeminor(unit, slice, part) \
    	(((slice) << 16) | (((unit) & 0x1e0) << 16) | \
    	(((unit) & 0x1f) << 3) | (part))
    static __inline dev_t
    dkmodpart(dev_t dev, int part)
    {
    	return (makedev(major(dev), (minor(dev) & ~7) | part));
    }
    static __inline dev_t
    dkmodslice(dev_t dev, int slice)
    {
    	return (makedev(major(dev), (minor(dev) & ~0x1f0000) | (slice << 16)));
    }
    #define	dkpart(dev)		(minor(dev) & 7)
    #define	dkslice(dev)		((minor(dev) >> 16) & 0x1f)
    #define	dktype(dev)       	((minor(dev) >> 25) & 0x7f)
    static __inline u_int
    dkunit(dev_t dev)
    {
    	return (((minor(dev) >> 16) & 0x1e0) | ((minor(dev) >> 3) & 0x1f));
    }
    struct	buf;
    struct	buf_queue_head;
    int	bounds_check_with_label(struct buf *bp, struct disklabel *lp,
    				int wlabel);
    void	diskerr(struct buf *bp, char *what, int pri, int blkdone,
    		struct disklabel *lp);
    void	disksort(struct buf *ap, struct buf *bp);
    u_int	dkcksum struct disklabel *lp);
    char	*readdisklabel(dev_t dev, struct disklabel *lp);
    void	bufqdisksort(struct buf_queue_head *ap, struct buf *bp);
    int	setdisklabel(struct disklabel *olp, struct disklabel *nlp,
    		     u_long openmask);
    int	writedisklabel(dev_t dev, struct disklabel *lp);
    #ifdef __alpha__
    void	alpha_fix_srm_checksum(struct buf *bp);
    #endif
    #endif /* _KERNEL */
    #endif /* LOCORE */
    #ifndef _KERNEL
    __BEGIN_DECLS
    struct disklabel *getdiskbyname(const char *);
    __END_DECLS
    #endif
    #endif /* !_SYS_DISKLABEL_H_ */

SEE ALSO
disktab(5), disklabel(8)