70 lines
3.2 KiB
C
70 lines
3.2 KiB
C
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/* Buffer (block) cache. To acquire a block, a routine calls get_block(),
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* telling which block it wants. The block is then regarded as "in use"
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* and has its 'b_count' field incremented. All the blocks that are not
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* in use are chained together in an LRU list, with 'front' pointing
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* to the least recently used block, and 'rear' to the most recently used
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* block. A reverse chain, using the field b_prev is also maintained.
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* Usage for LRU is measured by the time the put_block() is done. The second
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* parameter to put_block() can violate the LRU order and put a block on the
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* front of the list, if it will probably not be needed soon. If a block
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* is modified, the modifying routine must set b_dirt to DIRTY, so the block
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* will eventually be rewritten to the disk.
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*/
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#include <sys/dir.h> /* need struct direct */
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#include <dirent.h>
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EXTERN struct buf {
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/* Data portion of the buffer. */
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union {
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char b__data[MAX_BLOCK_SIZE]; /* ordinary user data */
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struct direct b__dir[NR_DIR_ENTRIES(MAX_BLOCK_SIZE)]; /* directory block */
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zone1_t b__v1_ind[V1_INDIRECTS]; /* V1 indirect block */
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zone_t b__v2_ind[V2_INDIRECTS(MAX_BLOCK_SIZE)]; /* V2 indirect block */
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d1_inode b__v1_ino[V1_INODES_PER_BLOCK]; /* V1 inode block */
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d2_inode b__v2_ino[V2_INODES_PER_BLOCK(MAX_BLOCK_SIZE)]; /* V2 inode block */
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bitchunk_t b__bitmap[BITMAP_CHUNKS(MAX_BLOCK_SIZE)]; /* bit map block */
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} b;
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/* Header portion of the buffer. */
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struct buf *b_next; /* used to link all free bufs in a chain */
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struct buf *b_prev; /* used to link all free bufs the other way */
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struct buf *b_hash; /* used to link bufs on hash chains */
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block_t b_blocknr; /* block number of its (minor) device */
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dev_t b_dev; /* major | minor device where block resides */
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char b_dirt; /* CLEAN or DIRTY */
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char b_count; /* number of users of this buffer */
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} buf[NR_BUFS];
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/* A block is free if b_dev == NO_DEV. */
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#define NIL_BUF ((struct buf *) 0) /* indicates absence of a buffer */
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/* These defs make it possible to use to bp->b_data instead of bp->b.b__data */
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#define b_data b.b__data
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#define b_dir b.b__dir
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#define b_v1_ind b.b__v1_ind
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#define b_v2_ind b.b__v2_ind
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#define b_v1_ino b.b__v1_ino
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#define b_v2_ino b.b__v2_ino
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#define b_bitmap b.b__bitmap
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EXTERN struct buf *buf_hash[NR_BUF_HASH]; /* the buffer hash table */
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EXTERN struct buf *front; /* points to least recently used free block */
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EXTERN struct buf *rear; /* points to most recently used free block */
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EXTERN int bufs_in_use; /* # bufs currently in use (not on free list)*/
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/* When a block is released, the type of usage is passed to put_block(). */
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#define WRITE_IMMED 0100 /* block should be written to disk now */
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#define ONE_SHOT 0200 /* set if block not likely to be needed soon */
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#define INODE_BLOCK 0 /* inode block */
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#define DIRECTORY_BLOCK 1 /* directory block */
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#define INDIRECT_BLOCK 2 /* pointer block */
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#define MAP_BLOCK 3 /* bit map */
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#define FULL_DATA_BLOCK 5 /* data, fully used */
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#define PARTIAL_DATA_BLOCK 6 /* data, partly used*/
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#define HASH_MASK (NR_BUF_HASH - 1) /* mask for hashing block numbers */
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