altblk(4)                                               altblk(4)



     NAME
          altblk - alternate block information for bad block handling

     SYNOPSIS
          #include <altblk.h>

     DESCRIPTION
          altblk is the data structure used by badblk(1M) to handle
          bad blocks for disk drives that support soft sector bad
          block remapping.

          The layout of this structure is as follows:

          #define  MAXALT     50      /* max alternate disk blocks */
          #define  ALTMAGIC   0xDBDF  /* bad block information
                                         is valid flag */

          /*
           *  structure for alternate block mapping
           */
          struct a_map {
                 long a_altbk;   /* bad block */
                 long a_index;   /* relative bad block index */
          };

          /*
           *  disk header block format for alternate block mapping
           */

          struct altblk {
             char a_fill[BSIZE-sizeof(struct a_map)-4*sizeof(long)];
                                      /* fill to make structure
                                         BSIZE bytes long */
              struct a_map a_map[1];  /* mapping */
              long a_magic;       /* verification code
                                         (ALTMAGIC) */
              long a_count;       /* bad block count */
              long a_nicbad;      /* max number of bad blocks */
              long a_maxalt;      /* max alt block used so far */
          };

          This structure describes the upper portion of block 0 of
          each physical disk.  The array amap is inverted (i.e., it
          is indexed backwards).  The specific fields in altblk are:

          amaxalt     the next usable block in bad block area
                       relative to the start of the bad block area

          anicbad     the maximum number of elements in the amap
                       structure

          acount      the number of bad blocks currently remapped on



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     altblk(4)                                               altblk(4)



                       the disk

          amagic      a magic number for verification

          amap        bad block remap information

     SEE ALSO
          badblk(1M).















































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