35 lines
1.3 KiB
C
35 lines
1.3 KiB
C
|
/* Buffer (block) cache. To acquire a block, a routine calls get_block(),
|
||
|
|
* telling which block it wants. The block is then regarded as "in use"
|
||
|
|
* and has its 'b_count' field incremented. All the blocks that are not
|
||
|
|
* in use are chained together in an LRU list, with 'front' pointing
|
||
|
|
* to the least recently used block, and 'rear' to the most recently used
|
||
|
|
* block. A reverse chain, using the field b_prev is also maintained.
|
||
|
|
* Usage for LRU is measured by the time the put_block() is done. The second
|
||
|
|
* parameter to put_block() can violate the LRU order and put a block on the
|
||
|
|
* front of the list, if it will probably not be needed soon. If a block
|
||
|
|
* is modified, the modifying routine must set b_dirt to DIRTY, so the block
|
||
|
|
* will eventually be rewritten to the disk.
|
||
|
|
*/
|
||
|
|
|
||
|
|
#ifndef EXT2_BUF_H
|
||
|
|
#define EXT2_BUF_H
|
||
|
|
|
||
|
|
#include <sys/dirent.h>
|
||
|
|
|
||
|
|
union fsdata_u {
|
||
|
|
char b__data[1]; /* ordinary user data */
|
||
|
|
/* indirect block */
|
||
|
|
block_t b__ind[1];
|
||
|
|
/* bit map block */
|
||
|
|
bitchunk_t b__bitmap[1];
|
||
|
|
};
|
||
|
|
|
||
|
|
/* A block is free if b_dev == NO_DEV. */
|
||
|
|
|
||
|
|
/* These defs make it possible to use to bp->b_data instead of bp->b.b__data */
|
||
|
|
#define b_data(bp) ((union fsdata_u *) bp->data)->b__data
|
||
|
|
#define b_ind(bp) ((union fsdata_u *) bp->data)->b__ind
|
||
|
|
#define b_bitmap(bp) ((union fsdata_u *) bp->data)->b__bitmap
|
||
|
|
|
||
|
|
#endif /* EXT2_BUF_H */
|