126 lines
4.2 KiB
C
126 lines
4.2 KiB
C
/* Second level block cache to supplement the file system cache. The block
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* cache of a 16-bit Minix system is very small, too small to prevent trashing.
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* A generic 32-bit system also doesn't have a very large cache to allow it
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* to run on systems with little memory. On a system with lots of memory one
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* can use the RAM disk as a read-only second level cache. Any blocks pushed
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* out of the primary cache are cached on the RAM disk. This code manages the
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* second level cache. The cache is a simple FIFO where old blocks are put
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* into and drop out at the other end. Must be searched backwards.
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*
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* The entry points into this file are:
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* init_cache2: initialize the second level cache
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* get_block2: get a block from the 2nd level cache
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* put_block2: store a block in the 2nd level cache
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* invalidate2: remove all the cache blocks on some device
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*/
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#include "fs.h"
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#include <minix/com.h>
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#include "buf.h"
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#if ENABLE_CACHE2
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#define MAX_BUF2 (256 * sizeof(char *))
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PRIVATE struct buf2 { /* 2nd level cache per block administration */
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block_t b2_blocknr; /* block number */
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dev_t b2_dev; /* device number */
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u16_t b2_count; /* count of in-cache block groups */
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} buf2[MAX_BUF2];
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PRIVATE unsigned nr_buf2; /* actual cache size */
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PRIVATE unsigned buf2_idx; /* round-robin reuse index */
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#define hash2(block) ((unsigned) ((block) & (MAX_BUF2 - 1)))
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/*===========================================================================*
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* init_cache2 *
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*===========================================================================*/
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PUBLIC void init_cache2(size)
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unsigned long size;
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{
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/* Initialize the second level disk buffer cache of 'size' blocks. */
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nr_buf2 = size > MAX_BUF2 ? MAX_BUF2 : (unsigned) size;
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}
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/*===========================================================================*
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* get_block2 *
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*===========================================================================*/
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PUBLIC int get_block2(bp, only_search)
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struct buf *bp; /* buffer to get from the 2nd level cache */
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int only_search; /* if NO_READ, do nothing, else act normal */
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{
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/* Fill a buffer from the 2nd level cache. Return true iff block acquired. */
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unsigned b;
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struct buf2 *bp2;
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/* If the block wanted is in the RAM disk then our game is over. */
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if (bp->b_dev == DEV_RAM) nr_buf2 = 0;
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/* Cache enabled? NO_READ? Any blocks with the same hash key? */
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if (nr_buf2 == 0 || only_search == NO_READ
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|| buf2[hash2(bp->b_blocknr)].b2_count == 0) return(0);
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/* Search backwards (there may be older versions). */
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b = buf2_idx;
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for (;;) {
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if (b == 0) b = nr_buf2;
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bp2 = &buf2[--b];
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if (bp2->b2_blocknr == bp->b_blocknr && bp2->b2_dev == bp->b_dev) break;
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if (b == buf2_idx) return(0);
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}
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/* Block is in the cache, get it. */
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if (dev_io(DEV_READ, DEV_RAM, FS_PROC_NR, bp->b_data,
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(off_t) b * BLOCK_SIZE, BLOCK_SIZE, 0) == BLOCK_SIZE) {
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return(1);
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}
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return(0);
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}
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/*===========================================================================*
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* put_block2 *
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*===========================================================================*/
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PUBLIC void put_block2(bp)
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struct buf *bp; /* buffer to store in the 2nd level cache */
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{
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/* Store a buffer into the 2nd level cache. */
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unsigned b;
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struct buf2 *bp2;
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if (nr_buf2 == 0) return; /* no 2nd level cache */
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b = buf2_idx++;
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if (buf2_idx == nr_buf2) buf2_idx = 0;
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bp2 = &buf2[b];
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if (dev_io(DEV_WRITE, DEV_RAM, FS_PROC_NR, bp->b_data,
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(off_t) b * BLOCK_SIZE, BLOCK_SIZE, 0) == BLOCK_SIZE) {
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if (bp2->b2_dev != NO_DEV) buf2[hash2(bp2->b2_blocknr)].b2_count--;
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bp2->b2_dev = bp->b_dev;
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bp2->b2_blocknr = bp->b_blocknr;
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buf2[hash2(bp2->b2_blocknr)].b2_count++;
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}
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}
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/*===========================================================================*
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* invalidate2 *
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*===========================================================================*/
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PUBLIC void invalidate2(device)
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dev_t device;
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{
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/* Invalidate all blocks from a given device in the 2nd level cache. */
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unsigned b;
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struct buf2 *bp2;
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for (b = 0; b < nr_buf2; b++) {
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bp2 = &buf2[b];
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if (bp2->b2_dev == device) {
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bp2->b2_dev = NO_DEV;
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buf2[hash2(bp2->b2_blocknr)].b2_count--;
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}
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}
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}
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#endif /* ENABLE_CACHE2 */
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