DISKLABEL(5)              OpenBSD 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 pro-
     vides detailed information about the geometry of the disk and the parti-
     tions into which the disk is divided.  It should be initialized when the
     disk is formatted, and may be changed later with the disklabel(8) pro-
     gram.  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 description of each partition con-
     tains 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 ge-
     ometry.  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 overwrit-
     ten by pack-to-pack copies or swap operations; the DIOCWLABEL ioctl(2),
     which is done as needed by the disklabel program, allows modification of
     the label sector.

     A copy of the in-core label for a disk can be obtained with the
     DIOCGDINFO ioctl; this works with a file descriptor for a block or char-
     acter (``raw'') device for any partition 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 la-
     bel was found on the disk, and the driver was able to construct only a
     skeletal label without partition information.  The DIOCWDINFO ioctl oper-
     ation 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.  The DIOCGPDINFO ioctl operation gets the de-
     fault label for a disk.  This simulates the case where there is no physi-
     cal label on the disk itself and can be used to see the label the kernel
     would construct in that case.  The DIOCRLDINFO ioctl operation causes the
     kernel to update its copy of label based on the physical label on the
     disk.  It can be used when the on-disk version of the label was changed
     directly or, if there is no physical label, to update the kernel's skele-
     tal label if some variable affecting label generation has changed (e.g.
     the fdisk partition table).  All of these operations are normally done
     using disklabel.

     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.
      */

     #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) /* disk magic number */

     #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" */
             /*
              * 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.
              */
             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

             /* 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 sects per track */
             u_int16_t       d_sparespercyl; /* # of spare sects 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 info */
     #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 */

             /* filesystem and partition information: */
             u_int16_t       d_npartitions;  /* # 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;        /* filesystem basic frag size */
                     u_int8_t        p_fstype;       /* filesystem type, see below */
                     u_int8_t        p_frag;         /* filesystem frags per block */
                     union {
                             u_int16_t       cpg;    /* UFS: FS cyls 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,
                                              * MAXPARTITIONS depends on the
                                              * architecture, and typically
                                              * varies between 8 and 16.
                                              */
     };

     /* 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 device */
     #define DTYPE_VND       12      /* vnode pseudo-disk */
     #define DTYPE_ATAPI     13      /* ATAPI */
     #define DTYPE_RAID      14      /* RAIDframe */

     #ifdef DKTYPENAMES
     static char *dktypenames[] = {
             "unknown",
             "SMD",
             "MSCP",
             "old DEC",
             "SCSI",
             "ESDI",
             "ST506",
             "HP-IB",
             "HP-FL",
             "type 9",
             "floppy",
             "ccd",
             "vnd",
             "ATAPI",
             "RAID",
             NULL
     };
     #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 */
     #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_ADOS         14      /* AmigaDOS fast file system */
     #define FS_HFS          15      /* Macintosh HFS */
     #define FS_ADFS         16      /* Acorn Disk Filing System */
     #define FS_EXT2FS       17      /* ext2fs */
     #define FS_CCD          18      /* ccd component */
     #define FS_RAID         19      /* RAIDframe */

     #ifdef  DKTYPENAMES
     static char *fstypenames[] = {
             "unused",
             "swap",
             "Version6",
             "Version7",
             "SystemV",
             "4.1BSD",
             "Eighth-Edition",
             "4.2BSD",
             "MSDOS",
             "4.4LFS",
             "unknown",
             "HPFS",
             "ISO9660",
             "boot",
             "ADOS",
             "HFS",
             "ADFS",
             "ext2fs",
             "ccd",
             "RAID",
             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;
     };

     /*
      * 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 */
     #define DIOCEJECT       _IO('d', 112)                /* eject disk */
     #define DIOCLOCK        _IOW('d', 113, int)          /* lock/unlock pack */

     #define DIOCGPDINFO     _IOR('d', 114, struct disklabel)/* get physical */
     #define DIOCRLDINFO     _IO('d', 115)                   /* reload disklabel */

     #endif /* LOCORE */

SEE ALSO
     disktab(5), disklabel(8)

OpenBSD 3.0                     August 6, 2001                               6
