minix/servers/pfs/buf.h

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2009-12-20 21:41:50 +01:00
/* Buffer (block) cache.
*/
struct buf {
/* Data portion of the buffer. */
char b_data[PIPE_BUF]; /* ordinary user data */
/* 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 */
ino_t b_num; /* inode number on minor device */
dev_t b_dev; /* major | minor device where block resides */
int b_bytes; /* Number of bytes allocated in bp */
int b_count; /* Number of users of this buffer */
};
/* A block is free if b_dev == NO_DEV. */
#define NIL_BUF ((struct buf *) 0) /* indicates absence of a buffer */
#define BUFHASH(b) ((b) % NR_BUFS)
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)*/