minix/servers/mfs/buf.h

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