| [4] | 1 | /* Buffer (block) cache. To acquire a block, a routine calls get_block(),
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| 2 | * telling which block it wants. The block is then regarded as "in use"
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| 3 | * and has its 'b_count' field incremented. All the blocks that are not
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| 4 | * in use are chained together in an LRU list, with 'front' pointing
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| 5 | * to the least recently used block, and 'rear' to the most recently used
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| 6 | * block. A reverse chain, using the field b_prev is also maintained.
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| 7 | * Usage for LRU is measured by the time the put_block() is done. The second
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| 8 | * parameter to put_block() can violate the LRU order and put a block on the
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| 9 | * front of the list, if it will probably not be needed soon. If a block
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| 10 | * is modified, the modifying routine must set b_dirt to DIRTY, so the block
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| 11 | * will eventually be rewritten to the disk.
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| 12 | */
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| 13 |
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| 14 | #include <sys/dir.h> /* need struct direct */
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| 15 | #include <dirent.h>
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| 16 |
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| 17 | EXTERN struct buf {
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| 18 | /* Data portion of the buffer. */
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| 19 | union {
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| 20 | char b__data[MAX_BLOCK_SIZE]; /* ordinary user data */
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| 21 | /* directory block */
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| 22 | struct direct b__dir[NR_DIR_ENTRIES(MAX_BLOCK_SIZE)];
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| 23 | /* V1 indirect block */
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| 24 | zone1_t b__v1_ind[V1_INDIRECTS];
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| 25 | /* V2 indirect block */
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| 26 | zone_t b__v2_ind[V2_INDIRECTS(MAX_BLOCK_SIZE)];
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| 27 | /* V1 inode block */
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| 28 | d1_inode b__v1_ino[V1_INODES_PER_BLOCK];
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| 29 | /* V2 inode block */
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| 30 | d2_inode b__v2_ino[V2_INODES_PER_BLOCK(MAX_BLOCK_SIZE)];
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| 31 | /* bit map block */
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| 32 | bitchunk_t b__bitmap[FS_BITMAP_CHUNKS(MAX_BLOCK_SIZE)];
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| 33 | } b;
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| 34 |
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| 35 | /* Header portion of the buffer. */
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| 36 | struct buf *b_next; /* used to link all free bufs in a chain */
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| 37 | struct buf *b_prev; /* used to link all free bufs the other way */
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| 38 | struct buf *b_hash; /* used to link bufs on hash chains */
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| 39 | block_t b_blocknr; /* block number of its (minor) device */
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| 40 | dev_t b_dev; /* major | minor device where block resides */
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| 41 | char b_dirt; /* CLEAN or DIRTY */
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| 42 | char b_count; /* number of users of this buffer */
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| 43 | } buf[NR_BUFS];
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| 44 |
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| 45 | /* A block is free if b_dev == NO_DEV. */
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| 46 |
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| 47 | #define NIL_BUF ((struct buf *) 0) /* indicates absence of a buffer */
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| 48 |
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| 49 | /* These defs make it possible to use to bp->b_data instead of bp->b.b__data */
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| 50 | #define b_data b.b__data
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| 51 | #define b_dir b.b__dir
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| 52 | #define b_v1_ind b.b__v1_ind
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| 53 | #define b_v2_ind b.b__v2_ind
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| 54 | #define b_v1_ino b.b__v1_ino
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| 55 | #define b_v2_ino b.b__v2_ino
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| 56 | #define b_bitmap b.b__bitmap
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| 57 |
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| 58 | EXTERN struct buf *buf_hash[NR_BUF_HASH]; /* the buffer hash table */
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| 59 |
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| 60 | EXTERN struct buf *front; /* points to least recently used free block */
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| 61 | EXTERN struct buf *rear; /* points to most recently used free block */
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| 62 | EXTERN int bufs_in_use; /* # bufs currently in use (not on free list)*/
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| 63 |
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| 64 | /* When a block is released, the type of usage is passed to put_block(). */
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| 65 | #define WRITE_IMMED 0100 /* block should be written to disk now */
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| 66 | #define ONE_SHOT 0200 /* set if block not likely to be needed soon */
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| 67 |
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| 68 | #define INODE_BLOCK 0 /* inode block */
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| 69 | #define DIRECTORY_BLOCK 1 /* directory block */
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| 70 | #define INDIRECT_BLOCK 2 /* pointer block */
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| 71 | #define MAP_BLOCK 3 /* bit map */
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| 72 | #define FULL_DATA_BLOCK 5 /* data, fully used */
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| 73 | #define PARTIAL_DATA_BLOCK 6 /* data, partly used*/
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| 74 |
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| 75 | #define HASH_MASK (NR_BUF_HASH - 1) /* mask for hashing block numbers */
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