servers/mfs/buf.h

   1 /* Buffer (block) cache.  To acquire a block, a routine calls get_block(),
   2  * telling which block it wants.  The block is then regarded as "in use"
   3  * and has its 'b_count' field incremented.  All the blocks that are not
   4  * in use are chained together in an LRU list, with 'front' pointing
   5  * to the least recently used block, and 'rear' to the most recently used
   6  * block.  A reverse chain, using the field b_prev is also maintained.
   7  * Usage for LRU is measured by the time the put_block() is done.  The second
   8  * parameter to put_block() can violate the LRU order and put a block on the
   9  * front of the list, if it will probably not be needed soon.  If a block
  10  * is modified, the modifying routine must set b_dirt to DIRTY, so the block
  11  * will eventually be rewritten to the disk.
  12  */
  13
  14 #include <sys/dir.h>                    /* need struct direct */
  15 #include <dirent.h>
  16
  17 union fsdata_u {
  18     char b__data[_MAX_BLOCK_SIZE];                   /* ordinary user data */
  19 /* directory block */
  20     struct direct b__dir[NR_DIR_ENTRIES(_MAX_BLOCK_SIZE)];
  21 /* V1 indirect block */
  22     zone1_t b__v1_ind[V1_INDIRECTS];
  23 /* V2 indirect block */
  24     zone_t  b__v2_ind[V2_INDIRECTS(_MAX_BLOCK_SIZE)];
  25 /* V1 inode block */
  26     d1_inode b__v1_ino[V1_INODES_PER_BLOCK];
  27 /* V2 inode block */
  28     d2_inode b__v2_ino[V2_INODES_PER_BLOCK(_MAX_BLOCK_SIZE)];
  29 /* bit map block */
  30     bitchunk_t b__bitmap[FS_BITMAP_CHUNKS(_MAX_BLOCK_SIZE)];
  31 };
  32
  33 /* A block is free if b_dev == NO_DEV. */
  34
  35 #define NIL_BUF ((struct buf *) 0)      /* indicates absence of a buffer */
  36
  37 /* These defs make it possible to use to bp->b_data instead of bp->b.b__data */
  38 #define b_data   bp->b__data
  39 #define b_dir    bp->b__dir
  40 #define b_v1_ind bp->b__v1_ind
  41 #define b_v2_ind bp->b__v2_ind
  42 #define b_v1_ino bp->b__v1_ino
  43 #define b_v2_ino bp->b__v2_ino
  44 #define b_bitmap bp->b__bitmap
  45
  46 #define BUFHASH(b) ((b) % nr_bufs)
  47
  48 EXTERN struct buf *front;       /* points to least recently used free block */
  49 EXTERN struct buf *rear;        /* points to most recently used free block */
  50 EXTERN int bufs_in_use;         /* # bufs currently in use (not on free list)*/
  51
  52 /* When a block is released, the type of usage is passed to put_block(). */
  53 #define WRITE_IMMED   0100 /* block should be written to disk now */
  54 #define ONE_SHOT      0200 /* set if block not likely to be needed soon */
  55
  56 #define INODE_BLOCK        0                             /* inode block */
  57 #define DIRECTORY_BLOCK    1                             /* directory block */
  58 #define INDIRECT_BLOCK     2                             /* pointer block */
  59 #define MAP_BLOCK          3                             /* bit map */
  60 #define FULL_DATA_BLOCK    5                             /* data, fully used */
  61 #define PARTIAL_DATA_BLOCK 6                             /* data, partly used*/
  62