1. 根目录:
2. fs
3. omfs
4. bitmap.c

#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/buffer_head.h>
#include <asm/div64.h>
#include "omfs.h"

unsigned long omfs_count_free(struct super_block *sb)
{
	unsigned int i;
	unsigned long sum = 0;
	struct omfs_sb_info *sbi = OMFS_SB(sb);
	int nbits = sb->s_blocksize * 8;

	for (i = 0; i < sbi->s_imap_size; i++)
		sum += nbits - bitmap_weight(sbi->s_imap[i], nbits);

	return sum;
}

/*
 *  Counts the run of zero bits starting at bit up to max.
 *  It handles the case where a run might spill over a buffer.
 *  Called with bitmap lock.
 */
static int count_run(unsigned long **addr, int nbits,
		int addrlen, int bit, int max)
{
	int count = 0;
	int x;

	for (; addrlen > 0; addrlen--, addr++) {
		x = find_next_bit(*addr, nbits, bit);
		count += x - bit;

		if (x < nbits || count > max)
			return min(count, max);

		bit = 0;
	}
	return min(count, max);
}

/*
 * Sets or clears the run of count bits starting with bit.
 * Called with bitmap lock.
 */
static int set_run(struct super_block *sb, int map,
		int nbits, int bit, int count, int set)
{
	int i;
	int err;
	struct buffer_head *bh;
	struct omfs_sb_info *sbi = OMFS_SB(sb);

 	err = -ENOMEM;
	bh = sb_bread(sb, clus_to_blk(sbi, sbi->s_bitmap_ino) + map);
	if (!bh)
		goto out;

	for (i = 0; i < count; i++, bit++) {
		if (bit >= nbits) {
			bit = 0;
			map++;

			mark_buffer_dirty(bh);
			brelse(bh);
			bh = sb_bread(sb,
				clus_to_blk(sbi, sbi->s_bitmap_ino) + map);
			if (!bh)
				goto out;
		}
		if (set) {
			set_bit(bit, sbi->s_imap[map]);
			set_bit(bit, (unsigned long *)bh->b_data);
		} else {
			clear_bit(bit, sbi->s_imap[map]);
			clear_bit(bit, (unsigned long *)bh->b_data);
		}
	}
	mark_buffer_dirty(bh);
	brelse(bh);
	err = 0;
out:
	return err;
}

/*
 * Tries to allocate exactly one block.  Returns true if successful.
 */
int omfs_allocate_block(struct super_block *sb, u64 block)
{
	struct buffer_head *bh;
	struct omfs_sb_info *sbi = OMFS_SB(sb);
	int bits_per_entry = 8 * sb->s_blocksize;
	unsigned int map, bit;
	int ret = 0;
	u64 tmp;

	tmp = block;
	bit = do_div(tmp, bits_per_entry);
	map = tmp;

	mutex_lock(&sbi->s_bitmap_lock);
	if (map >= sbi->s_imap_size || test_and_set_bit(bit, sbi->s_imap[map]))
		goto out;

	if (sbi->s_bitmap_ino > 0) {
		bh = sb_bread(sb, clus_to_blk(sbi, sbi->s_bitmap_ino) + map);
		if (!bh)
			goto out;

		set_bit(bit, (unsigned long *)bh->b_data);
		mark_buffer_dirty(bh);
		brelse(bh);
	}
	ret = 1;
out:
	mutex_unlock(&sbi->s_bitmap_lock);
	return ret;
}


/*
 *  Tries to allocate a set of blocks.	The request size depends on the
 *  type: for inodes, we must allocate sbi->s_mirrors blocks, and for file
 *  blocks, we try to allocate sbi->s_clustersize, but can always get away
 *  with just one block.
 */
int omfs_allocate_range(struct super_block *sb,
			int min_request,
			int max_request,
			u64 *return_block,
			int *return_size)
{
	struct omfs_sb_info *sbi = OMFS_SB(sb);
	int bits_per_entry = 8 * sb->s_blocksize;
	int ret = 0;
	int i, run, bit;

	mutex_lock(&sbi->s_bitmap_lock);
	for (i = 0; i < sbi->s_imap_size; i++) {
		bit = 0;
		while (bit < bits_per_entry) {
			bit = find_next_zero_bit(sbi->s_imap[i], bits_per_entry,
				bit);

			if (bit == bits_per_entry)
				break;

			run = count_run(&sbi->s_imap[i], bits_per_entry,
				sbi->s_imap_size-i, bit, max_request);

			if (run >= min_request)
				goto found;
			bit += run;
		}
	}
	ret = -ENOSPC;
	goto out;

found:
	*return_block = (u64) i * bits_per_entry + bit;
	*return_size = run;
	ret = set_run(sb, i, bits_per_entry, bit, run, 1);

out:
	mutex_unlock(&sbi->s_bitmap_lock);
	return ret;
}

/*
 * Clears count bits starting at a given block.
 */
int omfs_clear_range(struct super_block *sb, u64 block, int count)
{
	struct omfs_sb_info *sbi = OMFS_SB(sb);
	int bits_per_entry = 8 * sb->s_blocksize;
	u64 tmp;
	unsigned int map, bit;
	int ret;

	tmp = block;
	bit = do_div(tmp, bits_per_entry);
	map = tmp;

	if (map >= sbi->s_imap_size)
		return 0;

	mutex_lock(&sbi->s_bitmap_lock);
	ret = set_run(sb, map, bits_per_entry, bit, count, 0);
	mutex_unlock(&sbi->s_bitmap_lock);
	return ret;
}