70 lines
3.2 KiB
C
70 lines
3.2 KiB
C
/* 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 */
|
|
struct direct b__dir[NR_DIR_ENTRIES(MAX_BLOCK_SIZE)]; /* directory block */
|
|
zone1_t b__v1_ind[V1_INDIRECTS]; /* V1 indirect block */
|
|
zone_t b__v2_ind[V2_INDIRECTS(MAX_BLOCK_SIZE)]; /* V2 indirect block */
|
|
d1_inode b__v1_ino[V1_INODES_PER_BLOCK]; /* V1 inode block */
|
|
d2_inode b__v2_ino[V2_INODES_PER_BLOCK(MAX_BLOCK_SIZE)]; /* V2 inode block */
|
|
bitchunk_t b__bitmap[BITMAP_CHUNKS(MAX_BLOCK_SIZE)]; /* bit map block */
|
|
} 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(). */
|
|
#define WRITE_IMMED 0100 /* block should be written to disk now */
|
|
#define ONE_SHOT 0200 /* set if block not likely to be needed soon */
|
|
|
|
#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 */
|