servers/mfs/buf.h

   1 #ifndef __MFS_BUF_H__
   2 #define __MFS_BUF_H__
   3
   4 #include "clean.h"
   5
   6 /* Buffer (block) cache.  To acquire a block, a routine calls get_block(),
   7  * telling which block it wants.  The block is then regarded as "in use"
   8  * and has its 'b_count' field incremented.  All the blocks that are not
   9  * in use are chained together in an LRU list, with 'front' pointing
  10  * to the least recently used block, and 'rear' to the most recently used
  11  * block.  A reverse chain, using the field b_prev is also maintained.
  12  * Usage for LRU is measured by the time the put_block() is done.  The second
  13  * parameter to put_block() can violate the LRU order and put a block on the
  14  * front of the list, if it will probably not be needed soon.  If a block
  15  * is modified, the modifying routine must set b_dirt to DIRTY, so the block
  16  * will eventually be rewritten to the disk.
  17  */
  18
  19 #include <sys/dirent.h>
  20
  21 union fsdata_u {
  22     char b__data[1];                 /* ordinary user data */
  23 /* directory block */
  24     struct direct b__dir[1];
  25 /* V2 indirect block */
  26     zone_t  b__v2_ind[1];
  27 /* V2 inode block */
  28     d2_inode b__v2_ino[1];
  29 /* bit map block */
  30     bitchunk_t b__bitmap[1];
  31 };
  32
  33 /* A block is free if b_dev == NO_DEV. */
  34
  35
  36 /* These defs make it possible to use to bp->b_data instead of bp->b.b__data */
  37 #define b_data(b)   ((union fsdata_u *) b->data)->b__data
  38 #define b_dir(b)    ((union fsdata_u *) b->data)->b__dir
  39 #define b_v2_ind(b) ((union fsdata_u *) b->data)->b__v2_ind
  40 #define b_v2_ino(b) ((union fsdata_u *) b->data)->b__v2_ino
  41 #define b_bitmap(b) ((union fsdata_u *) b->data)->b__bitmap
  42
  43 #endif
  44