f78d8e74fd
A new call to vm lets processes yield a part of their memory to vm, together with an id, getting newly allocated memory in return. vm is allowed to forget about it if it runs out of memory. processes can ask for it back using the same id. (These two operations are normally combined in a single call.) It can be used as a as-big-as-memory-will-allow block cache for filesystems, which is how mfs now uses it.
62 lines
2.6 KiB
C
62 lines
2.6 KiB
C
/* 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/dir.h> /* need struct direct */
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#include <dirent.h>
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union fsdata_u {
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char b__data[_MAX_BLOCK_SIZE]; /* ordinary user data */
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/* directory block */
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struct direct b__dir[NR_DIR_ENTRIES(_MAX_BLOCK_SIZE)];
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/* V1 indirect block */
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zone1_t b__v1_ind[V1_INDIRECTS];
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/* V2 indirect block */
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zone_t b__v2_ind[V2_INDIRECTS(_MAX_BLOCK_SIZE)];
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/* V1 inode block */
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d1_inode b__v1_ino[V1_INODES_PER_BLOCK];
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/* V2 inode block */
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d2_inode b__v2_ino[V2_INODES_PER_BLOCK(_MAX_BLOCK_SIZE)];
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/* bit map block */
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bitchunk_t b__bitmap[FS_BITMAP_CHUNKS(_MAX_BLOCK_SIZE)];
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};
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/* A block is free if b_dev == NO_DEV. */
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#define NIL_BUF ((struct buf *) 0) /* indicates absence of a buffer */
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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 bp->b__data
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#define b_dir bp->b__dir
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#define b_v1_ind bp->b__v1_ind
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#define b_v2_ind bp->b__v2_ind
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#define b_v1_ino bp->b__v1_ino
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#define b_v2_ino bp->b__v2_ino
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#define b_bitmap bp->b__bitmap
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#define BUFHASH(b) ((b) % nr_bufs)
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EXTERN struct buf *front; /* points to least recently used free block */
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EXTERN struct buf *rear; /* points to most recently used free block */
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EXTERN int bufs_in_use; /* # bufs currently in use (not on free list)*/
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/* 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 */
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#define ONE_SHOT 0200 /* set if block not likely to be needed soon */
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#define INODE_BLOCK 0 /* inode block */
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#define DIRECTORY_BLOCK 1 /* directory block */
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#define INDIRECT_BLOCK 2 /* pointer block */
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#define MAP_BLOCK 3 /* bit map */
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#define FULL_DATA_BLOCK 5 /* data, fully used */
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#define PARTIAL_DATA_BLOCK 6 /* data, partly used*/
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