45 lines
1.6 KiB
C
45 lines
1.6 KiB
C
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#ifndef __MFS_BUF_H__
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#define __MFS_BUF_H__
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#include "clean.h"
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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/dirent.h>
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union fsdata_u {
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char b__data[1]; /* ordinary user data */
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/* directory block */
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struct direct b__dir[1];
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/* V2 indirect block */
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zone_t b__v2_ind[1];
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/* V2 inode block */
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d2_inode b__v2_ino[1];
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/* bit map block */
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bitchunk_t b__bitmap[1];
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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(b) ((union fsdata_u *) b->data)->b__data
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#define b_dir(b) ((union fsdata_u *) b->data)->b__dir
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#define b_v2_ind(b) ((union fsdata_u *) b->data)->b__v2_ind
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#define b_v2_ino(b) ((union fsdata_u *) b->data)->b__v2_ino
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#define b_bitmap(b) ((union fsdata_u *) b->data)->b__bitmap
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#endif
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