minix/servers/ext2/buf.h
Ben Gras f984dbba70 increase system-wide filename limit to 255
. move mfs-specific struct, constants to mfs/, so
	  mfs-specific, on-disk format structs and consts are
	  fully isolated from generic structs and functions
	. removes de and readfs utils
2011-08-17 16:00:01 +00:00

52 lines
2.2 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.
*/
#ifndef EXT2_BUF_H
#define EXT2_BUF_H
#include <dirent.h>
union fsdata_u {
char b__data[_MAX_BLOCK_SIZE]; /* ordinary user data */
/* indirect block */
block_t b__ind[_MAX_BLOCK_SIZE/sizeof(block_t)];
/* bit map block */
bitchunk_t b__bitmap[FS_BITMAP_CHUNKS(_MAX_BLOCK_SIZE)];
};
/* A block is free if b_dev == NO_DEV. */
/* These defs make it possible to use to bp->b_data instead of bp->b.b__data */
#define b_data bp->b__data
#define b_ind bp->b__ind
#define b_ino bp->b__ino
#define b_bitmap bp->b__bitmap
#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 unsigned 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*/
#endif /* EXT2_BUF_H */