442 lines
15 KiB
C
442 lines
15 KiB
C
/* The file system maintains a buffer cache to reduce the number of disk
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* accesses needed. Whenever a read or write to the disk is done, a check is
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* first made to see if the block is in the cache. This file manages the
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* cache.
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*
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* The entry points into this file are:
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* get_block: request to fetch a block for reading or writing from cache
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* put_block: return a block previously requested with get_block
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* alloc_zone: allocate a new zone (to increase the length of a file)
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* free_zone: release a zone (when a file is removed)
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* invalidate: remove all the cache blocks on some device
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*
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* Private functions:
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* rw_block: read or write a block from the disk itself
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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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#include "file.h"
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#include "fproc.h"
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#include "super.h"
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FORWARD _PROTOTYPE( void rm_lru, (struct buf *bp) );
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FORWARD _PROTOTYPE( int rw_block, (struct buf *, int) );
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/*===========================================================================*
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* get_block *
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*===========================================================================*/
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PUBLIC struct buf *get_block(dev, block, only_search)
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register dev_t dev; /* on which device is the block? */
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register block_t block; /* which block is wanted? */
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int only_search; /* if NO_READ, don't read, else act normal */
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{
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/* Check to see if the requested block is in the block cache. If so, return
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* a pointer to it. If not, evict some other block and fetch it (unless
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* 'only_search' is 1). All the blocks in the cache that are not in use
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* are linked together in a chain, with 'front' pointing to the least recently
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* used block and 'rear' to the most recently used block. If 'only_search' is
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* 1, the block being requested will be overwritten in its entirety, so it is
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* only necessary to see if it is in the cache; if it is not, any free buffer
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* will do. It is not necessary to actually read the block in from disk.
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* If 'only_search' is PREFETCH, the block need not be read from the disk,
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* and the device is not to be marked on the block, so callers can tell if
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* the block returned is valid.
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* In addition to the LRU chain, there is also a hash chain to link together
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* blocks whose block numbers end with the same bit strings, for fast lookup.
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*/
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int b;
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register struct buf *bp, *prev_ptr;
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/* Search the hash chain for (dev, block). Do_read() can use
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* get_block(NO_DEV ...) to get an unnamed block to fill with zeros when
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* someone wants to read from a hole in a file, in which case this search
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* is skipped
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*/
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if (dev != NO_DEV) {
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b = (int) block & HASH_MASK;
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bp = buf_hash[b];
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while (bp != NIL_BUF) {
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if (bp->b_blocknr == block && bp->b_dev == dev) {
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/* Block needed has been found. */
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if (bp->b_count == 0) rm_lru(bp);
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bp->b_count++; /* record that block is in use */
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return(bp);
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} else {
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/* This block is not the one sought. */
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bp = bp->b_hash; /* move to next block on hash chain */
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}
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}
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}
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/* Desired block is not on available chain. Take oldest block ('front'). */
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if ((bp = front) == NIL_BUF) panic(__FILE__,"all buffers in use", NR_BUFS);
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rm_lru(bp);
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/* Remove the block that was just taken from its hash chain. */
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b = (int) bp->b_blocknr & HASH_MASK;
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prev_ptr = buf_hash[b];
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if (prev_ptr == bp) {
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buf_hash[b] = bp->b_hash;
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} else {
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/* The block just taken is not on the front of its hash chain. */
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while (prev_ptr->b_hash != NIL_BUF)
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if (prev_ptr->b_hash == bp) {
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prev_ptr->b_hash = bp->b_hash; /* found it */
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break;
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} else {
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prev_ptr = prev_ptr->b_hash; /* keep looking */
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}
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}
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/* If the block taken is dirty, make it clean by writing it to the disk.
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* Avoid hysteresis by flushing all other dirty blocks for the same device.
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*/
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if (bp->b_dev != NO_DEV) {
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if (bp->b_dirt == DIRTY) flushall(bp->b_dev);
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#if ENABLE_CACHE2
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put_block2(bp);
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#endif
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}
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/* Fill in block's parameters and add it to the hash chain where it goes. */
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bp->b_dev = dev; /* fill in device number */
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bp->b_blocknr = block; /* fill in block number */
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bp->b_count++; /* record that block is being used */
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b = (int) bp->b_blocknr & HASH_MASK;
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bp->b_hash = buf_hash[b];
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buf_hash[b] = bp; /* add to hash list */
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/* Go get the requested block unless searching or prefetching. */
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if (dev != NO_DEV) {
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#if ENABLE_CACHE2
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if (get_block2(bp, only_search)) /* in 2nd level cache */;
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else
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#endif
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if (only_search == PREFETCH) bp->b_dev = NO_DEV;
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else
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if (only_search == NORMAL) {
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rw_block(bp, READING);
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}
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}
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return(bp); /* return the newly acquired block */
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}
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/*===========================================================================*
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* put_block *
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*===========================================================================*/
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PUBLIC void put_block(bp, block_type)
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register struct buf *bp; /* pointer to the buffer to be released */
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int block_type; /* INODE_BLOCK, DIRECTORY_BLOCK, or whatever */
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{
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/* Return a block to the list of available blocks. Depending on 'block_type'
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* it may be put on the front or rear of the LRU chain. Blocks that are
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* expected to be needed again shortly (e.g., partially full data blocks)
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* go on the rear; blocks that are unlikely to be needed again shortly
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* (e.g., full data blocks) go on the front. Blocks whose loss can hurt
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* the integrity of the file system (e.g., inode blocks) are written to
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* disk immediately if they are dirty.
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*/
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if (bp == NIL_BUF) return; /* it is easier to check here than in caller */
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bp->b_count--; /* there is one use fewer now */
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if (bp->b_count != 0) return; /* block is still in use */
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bufs_in_use--; /* one fewer block buffers in use */
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/* Put this block back on the LRU chain. If the ONE_SHOT bit is set in
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* 'block_type', the block is not likely to be needed again shortly, so put
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* it on the front of the LRU chain where it will be the first one to be
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* taken when a free buffer is needed later.
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*/
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if (bp->b_dev == DEV_RAM || block_type & ONE_SHOT) {
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/* Block probably won't be needed quickly. Put it on front of chain.
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* It will be the next block to be evicted from the cache.
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*/
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bp->b_prev = NIL_BUF;
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bp->b_next = front;
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if (front == NIL_BUF)
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rear = bp; /* LRU chain was empty */
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else
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front->b_prev = bp;
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front = bp;
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} else {
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/* Block probably will be needed quickly. Put it on rear of chain.
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* It will not be evicted from the cache for a long time.
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*/
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bp->b_prev = rear;
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bp->b_next = NIL_BUF;
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if (rear == NIL_BUF)
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front = bp;
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else
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rear->b_next = bp;
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rear = bp;
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}
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/* Some blocks are so important (e.g., inodes, indirect blocks) that they
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* should be written to the disk immediately to avoid messing up the file
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* system in the event of a crash.
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*/
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if ((block_type & WRITE_IMMED) && bp->b_dirt==DIRTY && bp->b_dev != NO_DEV) {
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rw_block(bp, WRITING);
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}
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}
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/*===========================================================================*
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* alloc_zone *
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*===========================================================================*/
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PUBLIC zone_t alloc_zone(dev, z)
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dev_t dev; /* device where zone wanted */
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zone_t z; /* try to allocate new zone near this one */
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{
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/* Allocate a new zone on the indicated device and return its number. */
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int major, minor;
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bit_t b, bit;
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struct super_block *sp;
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/* Note that the routine alloc_bit() returns 1 for the lowest possible
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* zone, which corresponds to sp->s_firstdatazone. To convert a value
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* between the bit number, 'b', used by alloc_bit() and the zone number, 'z',
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* stored in the inode, use the formula:
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* z = b + sp->s_firstdatazone - 1
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* Alloc_bit() never returns 0, since this is used for NO_BIT (failure).
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*/
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sp = get_super(dev);
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/* If z is 0, skip initial part of the map known to be fully in use. */
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if (z == sp->s_firstdatazone) {
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bit = sp->s_zsearch;
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} else {
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bit = (bit_t) z - (sp->s_firstdatazone - 1);
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}
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b = alloc_bit(sp, ZMAP, bit);
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if (b == NO_BIT) {
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err_code = ENOSPC;
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major = (int) (sp->s_dev >> MAJOR) & BYTE;
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minor = (int) (sp->s_dev >> MINOR) & BYTE;
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printf("No space on %sdevice %d/%d\n",
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sp->s_dev == root_dev ? "root " : "", major, minor);
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return(NO_ZONE);
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}
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if (z == sp->s_firstdatazone) sp->s_zsearch = b; /* for next time */
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return(sp->s_firstdatazone - 1 + (zone_t) b);
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}
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/*===========================================================================*
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* free_zone *
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*===========================================================================*/
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PUBLIC void free_zone(dev, numb)
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dev_t dev; /* device where zone located */
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zone_t numb; /* zone to be returned */
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{
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/* Return a zone. */
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register struct super_block *sp;
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bit_t bit;
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/* Locate the appropriate super_block and return bit. */
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sp = get_super(dev);
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if (numb < sp->s_firstdatazone || numb >= sp->s_zones) return;
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bit = (bit_t) (numb - (sp->s_firstdatazone - 1));
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free_bit(sp, ZMAP, bit);
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if (bit < sp->s_zsearch) sp->s_zsearch = bit;
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}
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/*===========================================================================*
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* rw_block *
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*===========================================================================*/
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PRIVATE int rw_block(bp, rw_flag)
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register struct buf *bp; /* buffer pointer */
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int rw_flag; /* READING or WRITING */
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{
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/* Read or write a disk block. This is the only routine in which actual disk
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* I/O is invoked. If an error occurs, a message is printed here, but the error
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* is not reported to the caller. If the error occurred while purging a block
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* from the cache, it is not clear what the caller could do about it anyway.
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*/
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int r, op;
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off_t pos;
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dev_t dev;
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int block_size;
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block_size = get_block_size(bp->b_dev);
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if ( (dev = bp->b_dev) != NO_DEV) {
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pos = (off_t) bp->b_blocknr * block_size;
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op = (rw_flag == READING ? DEV_READ : DEV_WRITE);
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r = dev_io(op, dev, FS_PROC_NR, bp->b_data, pos, block_size, 0);
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if (r != block_size) {
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if (r >= 0) r = END_OF_FILE;
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if (r != END_OF_FILE)
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printf("Unrecoverable disk error on device %d/%d, block %ld\n",
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(dev>>MAJOR)&BYTE, (dev>>MINOR)&BYTE, bp->b_blocknr);
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bp->b_dev = NO_DEV; /* invalidate block */
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/* Report read errors to interested parties. */
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if (rw_flag == READING) rdwt_err = r;
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}
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}
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bp->b_dirt = CLEAN;
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}
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/*===========================================================================*
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* invalidate *
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*===========================================================================*/
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PUBLIC void invalidate(device)
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dev_t device; /* device whose blocks are to be purged */
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{
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/* Remove all the blocks belonging to some device from the cache. */
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register struct buf *bp;
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for (bp = &buf[0]; bp < &buf[NR_BUFS]; bp++)
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if (bp->b_dev == device) bp->b_dev = NO_DEV;
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#if ENABLE_CACHE2
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invalidate2(device);
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#endif
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}
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/*===========================================================================*
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* flushall *
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*===========================================================================*/
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PUBLIC void flushall(dev)
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dev_t dev; /* device to flush */
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{
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/* Flush all dirty blocks for one device. */
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register struct buf *bp;
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static struct buf *dirty[NR_BUFS]; /* static so it isn't on stack */
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int ndirty;
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for (bp = &buf[0], ndirty = 0; bp < &buf[NR_BUFS]; bp++)
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if (bp->b_dirt == DIRTY && bp->b_dev == dev) dirty[ndirty++] = bp;
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rw_scattered(dev, dirty, ndirty, WRITING);
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}
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/*===========================================================================*
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* rw_scattered *
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*===========================================================================*/
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PUBLIC void rw_scattered(dev, bufq, bufqsize, rw_flag)
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dev_t dev; /* major-minor device number */
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struct buf **bufq; /* pointer to array of buffers */
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int bufqsize; /* number of buffers */
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int rw_flag; /* READING or WRITING */
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{
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/* Read or write scattered data from a device. */
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register struct buf *bp;
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int gap;
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register int i;
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register iovec_t *iop;
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static iovec_t iovec[NR_IOREQS]; /* static so it isn't on stack */
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int j, r;
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int block_size;
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block_size = get_block_size(dev);
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/* (Shell) sort buffers on b_blocknr. */
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gap = 1;
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do
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gap = 3 * gap + 1;
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while (gap <= bufqsize);
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while (gap != 1) {
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gap /= 3;
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for (j = gap; j < bufqsize; j++) {
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for (i = j - gap;
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i >= 0 && bufq[i]->b_blocknr > bufq[i + gap]->b_blocknr;
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i -= gap) {
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bp = bufq[i];
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bufq[i] = bufq[i + gap];
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bufq[i + gap] = bp;
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}
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}
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}
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/* Set up I/O vector and do I/O. The result of dev_io is OK if everything
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* went fine, otherwise the error code for the first failed transfer.
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*/
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while (bufqsize > 0) {
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for (j = 0, iop = iovec; j < NR_IOREQS && j < bufqsize; j++, iop++) {
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bp = bufq[j];
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if (bp->b_blocknr != bufq[0]->b_blocknr + j) break;
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iop->iov_addr = (vir_bytes) bp->b_data;
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iop->iov_size = block_size;
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}
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r = dev_io(rw_flag == WRITING ? DEV_SCATTER : DEV_GATHER,
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dev, FS_PROC_NR, iovec,
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(off_t) bufq[0]->b_blocknr * block_size, j, 0);
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/* Harvest the results. Dev_io reports the first error it may have
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* encountered, but we only care if it's the first block that failed.
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*/
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for (i = 0, iop = iovec; i < j; i++, iop++) {
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bp = bufq[i];
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if (iop->iov_size != 0) {
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/* Transfer failed. An error? Do we care? */
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if (r != OK && i == 0) {
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printf(
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"fs: I/O error on device %d/%d, block %lu\n",
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(dev>>MAJOR)&BYTE, (dev>>MINOR)&BYTE,
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bp->b_blocknr);
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bp->b_dev = NO_DEV; /* invalidate block */
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}
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break;
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}
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if (rw_flag == READING) {
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bp->b_dev = dev; /* validate block */
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put_block(bp, PARTIAL_DATA_BLOCK);
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} else {
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bp->b_dirt = CLEAN;
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}
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}
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bufq += i;
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bufqsize -= i;
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if (rw_flag == READING) {
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/* Don't bother reading more than the device is willing to
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* give at this time. Don't forget to release those extras.
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*/
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while (bufqsize > 0) {
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put_block(*bufq++, PARTIAL_DATA_BLOCK);
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bufqsize--;
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}
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}
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if (rw_flag == WRITING && i == 0) {
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/* We're not making progress, this means we might keep
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* looping. Buffers remain dirty if un-written. Buffers are
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* lost if invalidate()d or LRU-removed while dirty. This
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* is better than keeping unwritable blocks around forever..
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*/
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break;
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}
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}
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}
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/*===========================================================================*
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* rm_lru *
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*===========================================================================*/
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PRIVATE void rm_lru(bp)
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struct buf *bp;
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{
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/* Remove a block from its LRU chain. */
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struct buf *next_ptr, *prev_ptr;
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bufs_in_use++;
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next_ptr = bp->b_next; /* successor on LRU chain */
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prev_ptr = bp->b_prev; /* predecessor on LRU chain */
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if (prev_ptr != NIL_BUF)
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prev_ptr->b_next = next_ptr;
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else
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front = next_ptr; /* this block was at front of chain */
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if (next_ptr != NIL_BUF)
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next_ptr->b_prev = prev_ptr;
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else
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rear = prev_ptr; /* this block was at rear of chain */
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}
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