DISKLABEL(5)	    UNIX 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 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 infor-
     mation 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.  Addi-
     tional 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 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 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 gen-
     erally 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 parti-
     tion information.	Finally, the DIOCWDINFO ioctl(2) opera-
     tion 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:


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DISKLABEL(5)	    UNIX Programmer's Manual	     DISKLABEL(5)


     /*
      * 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.


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DISKLABEL(5)	    UNIX Programmer's Manual	     DISKLABEL(5)


	   */
     #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 */


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DISKLABEL(5)	    UNIX Programmer's Manual	     DISKLABEL(5)


	  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.


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DISKLABEL(5)	    UNIX Programmer's Manual	     DISKLABEL(5)


      */
     #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.


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DISKLABEL(5)	    UNIX Programmer's Manual	     DISKLABEL(5)


      * 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)


Printed 11/24/99	 April 21, 1995                         6


 
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