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->b__data
  31 #define b_ind bp->b__ind
  32 #define b_ino bp->b__ino
  33 #define b_bitmap bp->b__bitmap
  34
  35 #define BUFHASH(b) ((b) % nr_bufs)
  36
  37 EXTERN struct buf *front;    /* points to least recently used free block */
  38 EXTERN struct buf *rear;    /* points to most recently used free block */
  39 EXTERN unsigned int bufs_in_use; /* # bufs currently in use (not on free list)*/
  40
  41 /* When a block is released, the type of usage is passed to put_block(). */
  42 #define WRITE_IMMED   0100 /* block should be written to disk now */
  43 #define ONE_SHOT      0200 /* set if block not likely to be needed soon */
  44
  45 #define INODE_BLOCK        0                 /* inode block */
  46 #define DIRECTORY_BLOCK    1                 /* directory block */
  47 #define INDIRECT_BLOCK     2                 /* pointer block */
  48 #define MAP_BLOCK          3                 /* bit map */
  49 #define FULL_DATA_BLOCK    5                 /* data, fully used */
  50 #define PARTIAL_DATA_BLOCK 6                 /* data, partly used*/
  51
  52 #endif /* EXT2_BUF_H */