servers/ext2/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 #ifndef EXT2_BUF_H
  15 #define EXT2_BUF_H
  16
  17 #include <dirent.h>
  18
  19 union fsdata_u {
  20     char b__data[_MAX_BLOCK_SIZE];             /* ordinary user data */
  21 /* indirect block */
  22     block_t b__ind[_MAX_BLOCK_SIZE/sizeof(block_t)];
  23 /* bit map block */
  24     bitchunk_t b__bitmap[FS_BITMAP_CHUNKS(_MAX_BLOCK_SIZE)];
  25 };
  26
  27 /* A block is free if b_dev == NO_DEV. */
  28
  29 /* These defs make it possible to use to bp->b_data instead of bp->b.b__data */
  30 #define b_data(bp)   ((union fsdata_u *) bp->data)->b__data
  31 #define b_ind(bp) ((union fsdata_u *) bp->data)->b__ind
  32 #define b_bitmap(bp) ((union fsdata_u *) bp->data)->b__bitmap
  33
  34 #endif /* EXT2_BUF_H */