/*===========================================================================*
* set_blocksize *
*===========================================================================*/
void set_blocksize(struct super_block *sp)
{
int bufs;
cache_resize(sp->s_block_size, MINBUFS);
bufs = bufs_heuristic(sp);
cache_resize(sp->s_block_size, bufs);
/* Decide whether to use seconday cache or not.
* Only do this if
* - it's available, and
* - use of it hasn't been disabled for this fs, and
* - our main FS device isn't a memory device
*/
vmcache = 0;
if(vm_forgetblock(VM_BLOCKID_NONE) != ENOSYS &&
may_use_vmcache && major(sp->s_dev) != MEMORY_MAJOR) {
vmcache = 1;
}
}
/*===========================================================================*
* get_block *
*===========================================================================*/
struct buf *get_block(
register dev_t dev, /* on which device is the block? */
register block_t block, /* which block is wanted? */
int only_search /* if NO_READ, don't read, else act normal */
)
{
/* Check to see if the requested block is in the block cache. If so, return
* a pointer to it. If not, evict some other block and fetch it (unless
* 'only_search' is 1). All the blocks in the cache that are not in use
* are linked together in a chain, with 'front' pointing to the least recently
* used block and 'rear' to the most recently used block. If 'only_search' is
* 1, the block being requested will be overwritten in its entirety, so it is
* only necessary to see if it is in the cache; if it is not, any free buffer
* will do. It is not necessary to actually read the block in from disk.
* If 'only_search' is PREFETCH, the block need not be read from the disk,
* and the device is not to be marked on the block, so callers can tell if
* the block returned is valid.
* In addition to the LRU chain, there is also a hash chain to link together
* blocks whose block numbers end with the same bit strings, for fast lookup.
*/
int b;
static struct buf *bp, *prev_ptr;
u64_t yieldid = VM_BLOCKID_NONE, getid = make64(dev, block);
assert(buf_hash);
assert(buf);
assert(nr_bufs > 0);
ASSERT(fs_block_size > 0);
/* Search the hash chain for (dev, block). Do_read() can use
* get_block(NO_DEV ...) to get an unnamed block to fill with zeros when
* someone wants to read from a hole in a file, in which case this search
* is skipped
*/
if (dev != NO_DEV) {
b = BUFHASH(block);
bp = buf_hash[b];
while (bp != NULL) {
if (bp->b_blocknr == block && bp->b_dev == dev) {
/* Block needed has been found. */
if (bp->b_count == 0) rm_lru(bp);
bp->b_count++; /* record that block is in use */
ASSERT(bp->b_bytes == fs_block_size);
ASSERT(bp->b_dev == dev);
ASSERT(bp->b_dev != NO_DEV);
ASSERT(bp->bp);
return(bp);
} else {
/* This block is not the one sought. */
bp = bp->b_hash; /* move to next block on hash chain */
}
}
}
/* Desired block is not on available chain. Take oldest block ('front'). */
if ((bp = front) == NULL) panic("all buffers in use: %d", nr_bufs);
if(bp->b_bytes < fs_block_size) {
ASSERT(!bp->bp);
ASSERT(bp->b_bytes == 0);
if(!(bp->bp = alloc_contig( (size_t) fs_block_size, 0, NULL))) {
printf("MFS: couldn't allocate a new block.\n");
for(bp = front;
bp && bp->b_bytes < fs_block_size; bp = bp->b_next)
;
if(!bp) {
panic("no buffer available");
}
} else {
bp->b_bytes = fs_block_size;
}
}
ASSERT(bp);
ASSERT(bp->bp);
ASSERT(bp->b_bytes == fs_block_size);
ASSERT(bp->b_count == 0);
rm_lru(bp);
/* Remove the block that was just taken from its hash chain. */
b = BUFHASH(bp->b_blocknr);
prev_ptr = buf_hash[b];
if (prev_ptr == bp) {
buf_hash[b] = bp->b_hash;
} else {
/* The block just taken is not on the front of its hash chain. */
while (prev_ptr->b_hash != NULL)
if (prev_ptr->b_hash == bp) {
prev_ptr->b_hash = bp->b_hash; /* found it */
break;
} else {
prev_ptr = prev_ptr->b_hash; /* keep looking */
}
}
/* If the block taken is dirty, make it clean by writing it to the disk.
* Avoid hysteresis by flushing all other dirty blocks for the same device.
*/
if (bp->b_dev != NO_DEV) {
if (ISDIRTY(bp)) flushall(bp->b_dev);
/* Are we throwing out a block that contained something?
* Give it to VM for the second-layer cache.
*/
yieldid = make64(bp->b_dev, bp->b_blocknr);
assert(bp->b_bytes == fs_block_size);
BP_CLEARDEV(bp);
}
/* Fill in block's parameters and add it to the hash chain where it goes. */
if(dev == NO_DEV) BP_CLEARDEV(bp);
else BP_SETDEV(bp, dev);
bp->b_blocknr = block; /* fill in block number */
bp->b_count++; /* record that block is being used */
b = BUFHASH(bp->b_blocknr);
bp->b_hash = buf_hash[b];
buf_hash[b] = bp; /* add to hash list */
if(dev == NO_DEV) {
if(vmcache && cmp64(yieldid, VM_BLOCKID_NONE) != 0) {
vm_yield_block_get_block(yieldid, VM_BLOCKID_NONE,
bp->bp, fs_block_size);
}
return(bp); /* If the caller wanted a NO_DEV block, work is done. */
}
/* Go get the requested block unless searching or prefetching. */
if(only_search == PREFETCH || only_search == NORMAL) {
/* Block is not found in our cache, but we do want it
* if it's in the vm cache.
*/
if(vmcache) {
/* If we can satisfy the PREFETCH or NORMAL request
* from the vm cache, work is done.
*/
if(vm_yield_block_get_block(yieldid, getid,
bp->bp, fs_block_size) == OK) {
return bp;
}
}
}
if(only_search == PREFETCH) {
/* PREFETCH: don't do i/o. */
BP_CLEARDEV(bp);
} else if (only_search == NORMAL) {
read_block(bp);
} else if(only_search == NO_READ) {
/* we want this block, but its contents
* will be overwritten. VM has to forget
* about it.
*/
if(vmcache) {
vm_forgetblock(getid);
}
} else
panic("unexpected only_search value: %d", only_search);
assert(bp->bp);
return(bp); /* return the newly acquired block */
}
