| [9] | 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 | #include <dirent.h>
|
|---|
| 16 |
|
|---|
| 17 | EXTERN struct buf {
|
|---|
| 18 | /* Data portion of the buffer. */
|
|---|
| 19 | union {
|
|---|
| 20 | char b__data[_MAX_BLOCK_SIZE]; /* ordinary user data */
|
|---|
| 21 | /* directory block */
|
|---|
| 22 | struct direct b__dir[NR_DIR_ENTRIES(_MAX_BLOCK_SIZE)];
|
|---|
| 23 | /* V1 indirect block */
|
|---|
| 24 | zone1_t b__v1_ind[V1_INDIRECTS];
|
|---|
| 25 | /* V2 indirect block */
|
|---|
| 26 | zone_t b__v2_ind[V2_INDIRECTS(_MAX_BLOCK_SIZE)];
|
|---|
| 27 | /* V1 inode block */
|
|---|
| 28 | d1_inode b__v1_ino[V1_INODES_PER_BLOCK];
|
|---|
| 29 | /* V2 inode block */
|
|---|
| 30 | d2_inode b__v2_ino[V2_INODES_PER_BLOCK(_MAX_BLOCK_SIZE)];
|
|---|
| 31 | /* bit map block */
|
|---|
| 32 | bitchunk_t b__bitmap[FS_BITMAP_CHUNKS(_MAX_BLOCK_SIZE)];
|
|---|
| 33 | } b;
|
|---|
| 34 |
|
|---|
| 35 | /* Header portion of the buffer. */
|
|---|
| 36 | struct buf *b_next; /* used to link all free bufs in a chain */
|
|---|
| 37 | struct buf *b_prev; /* used to link all free bufs the other way */
|
|---|
| 38 | struct buf *b_hash; /* used to link bufs on hash chains */
|
|---|
| 39 | block_t b_blocknr; /* block number of its (minor) device */
|
|---|
| 40 | dev_t b_dev; /* major | minor device where block resides */
|
|---|
| 41 | char b_dirt; /* CLEAN or DIRTY */
|
|---|
| 42 | char b_count; /* number of users of this buffer */
|
|---|
| 43 | } buf[NR_BUFS];
|
|---|
| 44 |
|
|---|
| 45 | /* A block is free if b_dev == NO_DEV. */
|
|---|
| 46 |
|
|---|
| 47 | #define NIL_BUF ((struct buf *) 0) /* indicates absence of a buffer */
|
|---|
| 48 |
|
|---|
| 49 | /* These defs make it possible to use to bp->b_data instead of bp->b.b__data */
|
|---|
| 50 | #define b_data b.b__data
|
|---|
| 51 | #define b_dir b.b__dir
|
|---|
| 52 | #define b_v1_ind b.b__v1_ind
|
|---|
| 53 | #define b_v2_ind b.b__v2_ind
|
|---|
| 54 | #define b_v1_ino b.b__v1_ino
|
|---|
| 55 | #define b_v2_ino b.b__v2_ino
|
|---|
| 56 | #define b_bitmap b.b__bitmap
|
|---|
| 57 |
|
|---|
| 58 | EXTERN struct buf *buf_hash[NR_BUF_HASH]; /* the buffer hash table */
|
|---|
| 59 |
|
|---|
| 60 | EXTERN struct buf *front; /* points to least recently used free block */
|
|---|
| 61 | EXTERN struct buf *rear; /* points to most recently used free block */
|
|---|
| 62 | EXTERN int bufs_in_use; /* # bufs currently in use (not on free list)*/
|
|---|
| 63 |
|
|---|
| 64 | /* When a block is released, the type of usage is passed to put_block(). */
|
|---|
| 65 | #define WRITE_IMMED 0100 /* block should be written to disk now */
|
|---|
| 66 | #define ONE_SHOT 0200 /* set if block not likely to be needed soon */
|
|---|
| 67 |
|
|---|
| 68 | #define INODE_BLOCK 0 /* inode block */
|
|---|
| 69 | #define DIRECTORY_BLOCK 1 /* directory block */
|
|---|
| 70 | #define INDIRECT_BLOCK 2 /* pointer block */
|
|---|
| 71 | #define MAP_BLOCK 3 /* bit map */
|
|---|
| 72 | #define FULL_DATA_BLOCK 5 /* data, fully used */
|
|---|
| 73 | #define PARTIAL_DATA_BLOCK 6 /* data, partly used*/
|
|---|
| 74 |
|
|---|
| 75 | #define HASH_MASK (NR_BUF_HASH - 1) /* mask for hashing block numbers */
|
|---|
