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
16 EXTERN struct buf {
17 /* Data portion of the buffer. */
18 union {
19 char b__data[BLOCK_SIZE]; /* ordinary user data */
20 struct direct b__dir[NR_DIR_ENTRIES]; /* directory block */
21 zone1_t b__v1_ind[V1_INDIRECTS]; /* V1 indirect block */
22 zone_t b__v2_ind[V2_INDIRECTS]; /* V2 indirect block */
23 d1_inode b__v1_ino[V1_INODES_PER_BLOCK]; /* V1 inode block */
24 d2_inode b__v2_ino[V2_INODES_PER_BLOCK]; /* V2 inode block */
25 bitchunk_t b__bitmap[BITMAP_CHUNKS]; /* bit map block */
26 } b;
27
28 /* Header portion of the buffer. */
29 struct buf *b_next; /* used to link all free bufs in a chain */
30 struct buf *b_prev; /* used to link all free bufs the other way */
31 struct buf *b_hash; /* used to link bufs on hash chains */
32 block_t b_blocknr; /* block number of its (minor) device */
33 dev_t b_dev; /* major | minor device where block resides */
34 char b_dirt; /* CLEAN or DIRTY */
35 char b_count; /* number of users of this buffer */
36 } buf[NR_BUFS];
37
38 /* A block is free if b_dev == NO_DEV. */
39
40 #define NIL_BUF ((struct buf *) 0) /* indicates absence of a buffer */
41
42 /* These defs make it possible to use to bp->b_data instead of bp->b.b__data */
43 #define b_data b.b__data
44 #define b_dir b.b__dir
45 #define b_v1_ind b.b__v1_ind
46 #define b_v2_ind b.b__v2_ind
47 #define b_v1_ino b.b__v1_ino
48 #define b_v2_ino b.b__v2_ino
49 #define b_bitmap b.b__bitmap
50
51 EXTERN struct buf *buf_hash[NR_BUF_HASH]; /* the buffer hash table */
52
53 EXTERN struct buf *front; /* points to least recently used free block */
54 EXTERN struct buf *rear; /* points to most recently used free block */
55 EXTERN int bufs_in_use; /* # bufs currently in use (not on free list)*/
56
57 /* When a block is released, the type of usage is passed to put_block(). */
58 #define WRITE_IMMED 0100 /* block should be written to disk now */
59 #define ONE_SHOT 0200 /* set if block not likely to be needed soon */
60
61 #define INODE_BLOCK (0 + MAYBE_WRITE_IMMED) /* inode block */
62 #define DIRECTORY_BLOCK (1 + MAYBE_WRITE_IMMED) /* directory block */
63 #define INDIRECT_BLOCK (2 + MAYBE_WRITE_IMMED) /* pointer block */
64 #define MAP_BLOCK (3 + MAYBE_WRITE_IMMED) /* bit map */
65 #define ZUPER_BLOCK (4 + WRITE_IMMED + ONE_SHOT) /* super block */
66 #define FULL_DATA_BLOCK 5 /* data, fully used */
67 #define PARTIAL_DATA_BLOCK 6 /* data, partly used*/
68
69 #define HASH_MASK (NR_BUF_HASH - 1) /* mask for hashing block numbers */
70
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