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DISKLABEL(5)									     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 infor-
       mation 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 boot-
       strap  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 contains an identifier for the partition type  (standard	filesystem,  swap
       area,  etc.).   The filesystem updates the in-core copy of the label if it contains incom-
       plete 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 containing the label is normally made read-only so that it is not acciden-
       tally 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:

       /*
	* Disk description table, see disktab(5)
	*/
       #define	 _PATH_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.
	*/

       /* These should be defined per controller/drive elsewhere, not here! */
       #define LABELSECTOR 1		       /* sector containing label */
       #define LABELOFFSET 0		       /* offset of label in sector */

       #define DISKMAGIC ((u_long) 0x82564557) /* The disk magic number */
       #define	 MAXPARTITIONS	8

       /*
	* 2.11BSD's disklabels are different than 4.4BSD for a couple reasons:
	*
	*   1) D space is precious in the 2.11 kernel.	Many of the fields do
	*      not need to be 'long' (or even a 'short'), a 'short' (or 'char')
	*      is more than adequate.  If anyone ever ports the FFS to a PDP11
	*      changing the label format will be the least of the problems.
	*
	*   2) There is no need to support a bootblock more than 512 bytes long.
	*      The hardware (disk bootroms) only read the first sector, thus the
	*      label is always at sector 1 (the second half of the first file-
	*      system block).
	*
	* Almost all of the fields have been retained but with reduced sizes.
	* This is for future expansion and to ease the porting of the various
	* utilities which use the disklabel structure.	The 2.11 kernel uses
	* very little other than the partition tables.	Indeed only the
	* partition tables are resident in the kernel address space, the actual
	* label block is allocated external to the kernel and mapped in as
	* needed.
       */

       struct disklabel {
	    u_long    d_magic;		  /* the magic number */
	    u_char    d_type;		  /* drive type */
	    u_char    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 is the (optional) name of the primary (block 0) bootstrap
	     * as found in /mdec.  This is 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 */
		 char *un_d_boot0;	  /* primary bootstrap name */
	    } d_un;
       #define d_packname  d_un.un_d_packname
       #define d_boot0		d_un.un_d_boot0
       #endif	 /* ! KERNEL or STANDALONE */
			   /* disk geometry: */
	    u_short   d_secsize;	  /* # of bytes per sector */
	    u_short   d_nsectors;	  /* # of data sectors per track */
	    u_short   d_ntracks;	  /* # of tracks per cylinder */
	    u_short   d_ncylinders;	  /* # of data cylinders per unit */
	    u_short   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_short   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_char    d_interleave;	  /* hardware sector interleave */
	    u_char    d_trackskew;	  /* sector 0 skew, per track */
	    u_char    d_cylskew;	  /* sector 0 skew, per cylinder */
	    u_char    d_headswitch;	  /* head swith time, usec */
	    u_short   d_trkseek;	  /* track-to-track seek, msec */
	    u_short   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_short   d_bbsize; 	  /* size of boot area at sn0, bytes */
	    u_short   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_short   p_fsize;	  /* filesystem basic fragment size */
		 u_char    p_fstype;	  /* filesystem type, see below */
		 u_char    p_frag;	  /* filesystem fragments per block */
	    } 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	7	  /* floppy */

       #ifdef DKTYPENAMES
       static char *dktypenames[] = {
	    "unknown",
	    "SMD",
	    "MSCP",
	    "old DEC",
	    "SCSI",
	    "ESDI",
	    "ST506",
	    "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 */
       /*
	* 2.11BSD uses type 5 filesystems even though block numbers are 4 bytes
	* (rather than the packed 3 byte format) and the directory structure is
	* that of 4.3BSD (long filenames).
       */
       #define	 FS_V71K	5	  /* V7 with 1K blocks (4.1,2.9,2.11) */
       #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 file system */
       #define	 FS_OTHER	10	  /* in use, but unknown/unsupported */
       #define	 FS_HPFS	11	  /* OS/2 high-performance filesystem */
       #define	 FS_ISO9660	12	  /* ISO 9660, normally CD-ROM */

       #ifdef	 DKTYPENAMES
       static char *fstypenames[] = {
	    "unused",
	    "swap",
	    "Version 6",
	    "Version 7",
	    "System V",
	    "2.11BSD",
	    "Eighth Edition",
	    "4.2BSD",
	    "MSDOS",
	    "4.4LFS",
	    "unknown",
	    "HPFS",
	    "ISO9660",
	    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 */

       /*
	* 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 */

       #ifndef	 KERNEL
       struct disklabel *getdiskbyname();
       #endif

SEE ALSO
       disklabel(8)

3rd Berkeley Distribution		  April 21, 1995			     DISKLABEL(5)
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