balloc.c

LINUX1.0内核源代码,学习LINUX编程的一定要看。

		    unsigned long * prealloc_block)
{
	struct buffer_head * bh;
	struct buffer_head * bh2;
	char * p, * r;
	int i, j, k, tmp;
	unsigned long lmap;
	int bitmap_nr;
	struct ext2_group_desc * gdp;
	struct ext2_super_block * es;

#ifdef EXT2FS_DEBUG
	static int goal_hits = 0, goal_attempts = 0;
#endif
	if (!sb) {
		printk ("ext2_new_block: nonexistent device");
		return 0;
	}
	lock_super (sb);
	es = sb->u.ext2_sb.s_es;
	if (es->s_free_blocks_count <= es->s_r_blocks_count && !suser()) {
		unlock_super (sb);
		return 0;
	}

	ext2_debug ("goal=%lu.\n", goal);

repeat:
	/*
	 * First, test whether the goal block is free.
	 */
	if (goal < es->s_first_data_block || goal >= es->s_blocks_count)
		goal = es->s_first_data_block;
	i = (goal - es->s_first_data_block) / EXT2_BLOCKS_PER_GROUP(sb);
	gdp = get_group_desc (sb, i, &bh2);
	if (gdp->bg_free_blocks_count > 0) {
		j = ((goal - es->s_first_data_block) % EXT2_BLOCKS_PER_GROUP(sb));
#ifdef EXT2FS_DEBUG
		if (j)
			goal_attempts++;
#endif
		bitmap_nr = load_block_bitmap (sb, i);
		bh = sb->u.ext2_sb.s_block_bitmap[bitmap_nr];

		ext2_debug ("goal is at %d:%d.\n", i, j);

		if (!test_bit(j, bh->b_data)) {
#ifdef EXT2FS_DEBUG
			goal_hits++;
			ext2_debug ("goal bit allocated.\n");
#endif
			goto got_block;
		}
		if (j) {
			/*
			 * The goal was occupied; search forward for a free 
			 * block within the next 32 blocks
			 */
			lmap = ((((unsigned long *) bh->b_data)[j >> 5]) >>
				((j & 31) + 1));
			if (j < EXT2_BLOCKS_PER_GROUP(sb) - 32)
				lmap |= (((unsigned long *) bh->b_data)[(j >> 5) + 1]) <<
				 (31 - (j & 31));
			else
				lmap |= 0xffffffff << (31 - (j & 31));
			if (lmap != 0xffffffffl) {
				__asm__ ("bsfl %1,%0"
					 : "=r" (k)
					 : "r" (~lmap));
				k++;
				if ((j + k) < EXT2_BLOCKS_PER_GROUP(sb)) {
					j += k;
					goto got_block;
				}
			}
		}
	
		ext2_debug ("Bit not found near goal\n");

		/*
		 * There has been no free block found in the near vicinity
		 * of the goal: do a search forward through the block groups,
		 * searching in each group first for an entire free byte in
		 * the bitmap and then for any free bit.
		 * 
		 * Search first in the remainder of the current group; then,
		 * cyclicly search throught the rest of the groups.
		 */
		p = ((char *) bh->b_data) + (j >> 3);
		r = find_first_zero_byte (p, 
					  (EXT2_BLOCKS_PER_GROUP(sb) - j + 7) >> 3);
		k = (r - ((char *) bh->b_data)) << 3;
		if (k < EXT2_BLOCKS_PER_GROUP(sb)) {
			j = k;
			goto search_back;
		}
		k = find_next_zero_bit ((unsigned long *) bh->b_data, 
					EXT2_BLOCKS_PER_GROUP(sb),
					j);
		if (k < EXT2_BLOCKS_PER_GROUP(sb)) {
			j = k;
			goto got_block;
		}
	}

	ext2_debug ("Bit not found in block group %d.\n", i);

	/*
	 * Now search the rest of the groups.  We assume that 
	 * i and gdp correctly point to the last group visited.
	 */
	for (k = 0; k < sb->u.ext2_sb.s_groups_count; k++) {
		i++;
		if (i >= sb->u.ext2_sb.s_groups_count)
			i = 0;
		gdp = get_group_desc (sb, i, &bh2);
		if (gdp->bg_free_blocks_count > 0)
			break;
	}
	if (k >= sb->u.ext2_sb.s_groups_count) {
		unlock_super (sb);
		return 0;
	}
	bitmap_nr = load_block_bitmap (sb, i);
	bh = sb->u.ext2_sb.s_block_bitmap[bitmap_nr];
	r = find_first_zero_byte (bh->b_data, 
				  EXT2_BLOCKS_PER_GROUP(sb) >> 3);
	j = (r - bh->b_data) << 3;
	if (j < EXT2_BLOCKS_PER_GROUP(sb))
		goto search_back;
	else
		j = find_first_zero_bit ((unsigned long *) bh->b_data,
					 EXT2_BLOCKS_PER_GROUP(sb));
	if (j >= EXT2_BLOCKS_PER_GROUP(sb)) {
		ext2_error (sb, "ext2_new_block",
			    "Free blocks count corrupted for block group %d", i);
		unlock_super (sb);
		return 0;
	}

search_back:
	/* 
	 * We have succeeded in finding a free byte in the block
	 * bitmap.  Now search backwards up to 7 bits to find the
	 * start of this group of free blocks.
	 */
	for (k = 0; k < 7 && j > 0 && !test_bit (j - 1, bh->b_data); k++, j--);
	
got_block:

	ext2_debug ("using block group %d(%d)\n", i, gdp->bg_free_blocks_count);

	tmp = j + i * EXT2_BLOCKS_PER_GROUP(sb) + es->s_first_data_block;

	if (test_opt (sb, CHECK_STRICT) &&
	    (tmp == gdp->bg_block_bitmap ||
	     tmp == gdp->bg_inode_bitmap ||
	     in_range (tmp, gdp->bg_inode_table, sb->u.ext2_sb.s_itb_per_group)))
		ext2_panic (sb, "ext2_new_block",
			    "Allocating block in system zone\n"
			    "block = %u", tmp);

	if (set_bit (j, bh->b_data)) {
		ext2_warning (sb, "ext2_new_block",
			      "bit already set for block %d", j);
		goto repeat;
	}

	ext2_debug ("found bit %d\n", j);

	/*
	 * Do block preallocation now if required.
	 */
#ifdef EXT2_PREALLOCATE
	if (prealloc_block) {
		*prealloc_count = 0;
		*prealloc_block = tmp + 1;
		for (k = 1;
		     k < 8 && (j + k) < EXT2_BLOCKS_PER_GROUP(sb); k++) {
			if (set_bit (j + k, bh->b_data))
				break;
			(*prealloc_count)++;
		}	
		gdp->bg_free_blocks_count -= *prealloc_count;
		es->s_free_blocks_count -= *prealloc_count;
		ext2_debug ("Preallocated a further %lu bits.\n",
			    *prealloc_count);
	}
#endif

	j = tmp;

	bh->b_dirt = 1;
	if (sb->s_flags & MS_SYNC) {
		ll_rw_block (WRITE, 1, &bh);
		wait_on_buffer (bh);
	}

	if (j >= es->s_blocks_count) {
		ext2_error (sb, "ext2_new_block",
			    "block >= blocks count\n"
			    "block_group = %d, block=%d", i, j);
		unlock_super (sb);
		return 0;
	}
	if (!(bh = getblk (sb->s_dev, j, sb->s_blocksize))) {
		ext2_error (sb, "ext2_new_block", "cannot get block %d", j);
		unlock_super (sb);
		return 0;
	}
	clear_block (bh->b_data, sb->s_blocksize);
	bh->b_uptodate = 1;
	bh->b_dirt = 1;
	brelse (bh);

	ext2_debug ("allocating block %d. "
		    "Goal hits %d of %d.\n", j, goal_hits, goal_attempts);

	gdp->bg_free_blocks_count--;
	bh2->b_dirt = 1;
	es->s_free_blocks_count--;
	sb->u.ext2_sb.s_sbh->b_dirt = 1;
	sb->s_dirt = 1;
	unlock_super (sb);
	return j;
}

unsigned long ext2_count_free_blocks (struct super_block * sb)
{
#ifdef EXT2FS_DEBUG
	struct ext2_super_block * es;
	unsigned long desc_count, bitmap_count, x;
	int bitmap_nr;
	struct ext2_group_desc * gdp;
	int i;
	
	lock_super (sb);
	es = sb->u.ext2_sb.s_es;
	desc_count = 0;
	bitmap_count = 0;
	gdp = NULL;
	for (i = 0; i < sb->u.ext2_sb.s_groups_count; i++) {
		gdp = get_group_desc (sb, i, NULL);
		desc_count += gdp->bg_free_blocks_count;
		bitmap_nr = load_block_bitmap (sb, i);
		x = ext2_count_free (sb->u.ext2_sb.s_block_bitmap[bitmap_nr],
				     sb->s_blocksize);
		printk ("group %d: stored = %d, counted = %lu\n",
			i, gdp->bg_free_blocks_count, x);
		bitmap_count += x;
	}
	printk("ext2_count_free_blocks: stored = %lu, computed = %lu, %lu\n",
	       es->s_free_blocks_count, desc_count, bitmap_count);
	unlock_super (sb);
	return bitmap_count;
#else
	return sb->u.ext2_sb.s_es->s_free_blocks_count;
#endif
}

static inline int block_in_use (unsigned long block,
				struct super_block * sb,
				unsigned char * map)
{
	return test_bit ((block - sb->u.ext2_sb.s_es->s_first_data_block) %
			 EXT2_BLOCKS_PER_GROUP(sb), map);
}

void ext2_check_blocks_bitmap (struct super_block * sb)
{
	struct buffer_head * bh;
	struct ext2_super_block * es;
	unsigned long desc_count, bitmap_count, x;
	unsigned long desc_blocks;
	int bitmap_nr;
	struct ext2_group_desc * gdp;
	int i, j;

	lock_super (sb);
	es = sb->u.ext2_sb.s_es;
	desc_count = 0;
	bitmap_count = 0;
	gdp = NULL;
	desc_blocks = (sb->u.ext2_sb.s_groups_count + EXT2_DESC_PER_BLOCK(sb) - 1) /
		      EXT2_DESC_PER_BLOCK(sb);
	for (i = 0; i < sb->u.ext2_sb.s_groups_count; i++) {
		gdp = get_group_desc (sb, i, NULL);
		desc_count += gdp->bg_free_blocks_count;
		bitmap_nr = load_block_bitmap (sb, i);
		bh = sb->u.ext2_sb.s_block_bitmap[bitmap_nr];

		if (!test_bit (0, bh->b_data))
			ext2_error (sb, "ext2_check_blocks_bitmap",
				    "Superblock in group %d is marked free", i);

		for (j = 0; j < desc_blocks; j++)
			if (!test_bit (j + 1, bh->b_data))
				ext2_error (sb, "ext2_check_blocks_bitmap",
					    "Descriptor block #%d in group "
					    "%d is marked free", j, i);

		if (!block_in_use (gdp->bg_block_bitmap, sb, bh->b_data))
			ext2_error (sb, "ext2_check_blocks_bitmap",
				    "Block bitmap for group %d is marked free",
				    i);

		if (!block_in_use (gdp->bg_inode_bitmap, sb, bh->b_data))
			ext2_error (sb, "ext2_check_blocks_bitmap",
				    "Inode bitmap for group %d is marked free",
				    i);

		for (j = 0; j < sb->u.ext2_sb.s_itb_per_group; j++)
			if (!block_in_use (gdp->bg_inode_table + j, sb, bh->b_data))
				ext2_error (sb, "ext2_check_blocks_bitmap",
					    "Block #%d of the inode table in "
					    "group %d is marked free", j, i);

		x = ext2_count_free (bh, sb->s_blocksize);
		if (gdp->bg_free_blocks_count != x)
			ext2_error (sb, "ext2_check_blocks_bitmap",
				    "Wrong free blocks count for group %d, "
				    "stored = %d, counted = %lu", i,
				    gdp->bg_free_blocks_count, x);
		bitmap_count += x;
	}
	if (es->s_free_blocks_count != bitmap_count)
		ext2_error (sb, "ext2_check_blocks_bitmap",
			    "Wrong free blocks count in super block, "
			    "stored = %lu, counted = %lu",
			    es->s_free_blocks_count, bitmap_count);
	unlock_super (sb);
}