53 lines
2.2 KiB
C
53 lines
2.2 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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#ifndef EXT2_BUF_H
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#define EXT2_BUF_H
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#include <dirent.h>
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union fsdata_u {
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char b__data[_MAX_BLOCK_SIZE]; /* ordinary user data */
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/* indirect block */
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block_t b__ind[_MAX_BLOCK_SIZE/sizeof(block_t)];
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/* bit map block */
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bitchunk_t b__bitmap[FS_BITMAP_CHUNKS(_MAX_BLOCK_SIZE)];
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};
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/* A block is free if b_dev == NO_DEV. */
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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 bp->b__data
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#define b_ind bp->b__ind
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#define b_ino bp->b__ino
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#define b_bitmap bp->b__bitmap
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#define BUFHASH(b) ((b) % nr_bufs)
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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 unsigned 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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#endif /* EXT2_BUF_H */
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