btrfs-progs: Pull free space tree related code from kernel

To help implement free space tree checker in user space some kernel
function are necessary, namely iterating/deleting/adding freespace
items, some internal search functions. Functions to populate a block
group based on the extent tree. The code is largely copy/paste from
the kernel with locking eliminated (i.e free_space_lock). It supports
reading/writing of both bitmap and extent based FST trees.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 1243 insertions, 6 deletions

diff --git a/free-space-tree.c b/free-space-tree.c
index b439b6b4..6641cdfa 100644
--- a/free-space-tree.c
+++ b/free-space-tree.c
@@ -21,6 +21,37 @@
 #include "free-space-cache.h"
 #include "free-space-tree.h"
 #include "transaction.h"
+#include "bitops.h"
+#include "internal.h"
+
+void set_free_space_tree_thresholds(struct btrfs_block_group_cache *cache,
+				    u64 sectorsize)
+{
+	u32 bitmap_range;
+	size_t bitmap_size;
+	u64 num_bitmaps, total_bitmap_size;
+
+	/*
+	 * We convert to bitmaps when the disk space required for using extents
+	 * exceeds that required for using bitmaps.
+	 */
+	bitmap_range = sectorsize * BTRFS_FREE_SPACE_BITMAP_BITS;
+	num_bitmaps = div_u64(cache->key.offset + bitmap_range - 1,
+			      bitmap_range);
+	bitmap_size = sizeof(struct btrfs_item) + BTRFS_FREE_SPACE_BITMAP_SIZE;
+	total_bitmap_size = num_bitmaps * bitmap_size;
+	cache->bitmap_high_thresh = div_u64(total_bitmap_size,
+					    sizeof(struct btrfs_item));
+
+	/*
+	 * We allow for a small buffer between the high threshold and low
+	 * threshold to avoid thrashing back and forth between the two formats.
+	 */
+	if (cache->bitmap_high_thresh > 100)
+		cache->bitmap_low_thresh = cache->bitmap_high_thresh - 100;
+	else
+		cache->bitmap_low_thresh = 0;
+}
 
 static struct btrfs_free_space_info *
 search_free_space_info(struct btrfs_trans_handle *trans,
@@ -47,8 +78,7 @@ search_free_space_info(struct btrfs_trans_handle *trans,
 }
 
 static int free_space_test_bit(struct btrfs_block_group_cache *block_group,
-			       struct btrfs_path *path, u64 offset,
-			       u64 sectorsize)
+			       struct btrfs_path *path, u64 offset)
 {
 	struct extent_buffer *leaf;
 	struct btrfs_key key;
@@ -64,10 +94,1080 @@ static int free_space_test_bit(struct btrfs_block_group_cache *block_group,
 	ASSERT(offset >= found_start && offset < found_end);
 
 	ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
-	i = (offset - found_start) / sectorsize;
+	i = (offset - found_start) / leaf->fs_info->sectorsize;
 	return !!extent_buffer_test_bit(leaf, ptr, i);
 }
 
+/*
+ * btrfs_search_slot() but we're looking for the greatest key less than the
+ * passed key.
+ */
+static int btrfs_search_prev_slot(struct btrfs_trans_handle *trans,
+				  struct btrfs_root *root,
+				  struct btrfs_key *key, struct btrfs_path *p,
+				  int ins_len, int cow)
+{
+	int ret;
+
+	ret = btrfs_search_slot(trans, root, key, p, ins_len, cow);
+	if (ret < 0)
+		return ret;
+
+	if (ret == 0) {
+		ASSERT(0);
+		return -EIO;
+	}
+
+	if (p->slots[0] == 0) {
+		ASSERT(0);
+		return -EIO;
+	}
+	p->slots[0]--;
+
+	return 0;
+}
+
+static int add_new_free_space_info(struct btrfs_trans_handle *trans,
+				   struct btrfs_block_group_cache *block_group,
+				   struct btrfs_path *path)
+{
+	struct btrfs_root *root = trans->fs_info->free_space_root;
+	struct btrfs_free_space_info *info;
+	struct btrfs_key key;
+	struct extent_buffer *leaf;
+	int ret;
+
+	key.objectid = block_group->key.objectid;
+	key.type = BTRFS_FREE_SPACE_INFO_KEY;
+	key.offset = block_group->key.offset;
+
+	ret = btrfs_insert_empty_item(trans, root, path, &key, sizeof(*info));
+	if (ret)
+		goto out;
+
+	leaf = path->nodes[0];
+	info = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_free_space_info);
+	btrfs_set_free_space_extent_count(leaf, info, 0);
+	btrfs_set_free_space_flags(leaf, info, 0);
+	btrfs_mark_buffer_dirty(leaf);
+
+	ret = 0;
+out:
+	btrfs_release_path(path);
+	return ret;
+}
+
+static inline u32 free_space_bitmap_size(u64 size, u32 sectorsize)
+{
+	return DIV_ROUND_UP((u32)div_u64(size, sectorsize), BITS_PER_BYTE);
+}
+
+static unsigned long *alloc_bitmap(u32 bitmap_size)
+{
+	unsigned long *ret;
+	unsigned int nofs_flag;
+	u32 bitmap_rounded_size = round_up(bitmap_size, sizeof(unsigned long));
+
+	/*
+	 * GFP_NOFS doesn't work with kvmalloc(), but we really can't recurse
+	 * into the filesystem as the free space bitmap can be modified in the
+	 * critical section of a transaction commit.
+	 *
+	 * TODO: push the memalloc_nofs_{save,restore}() to the caller where we
+	 * know that recursion is unsafe.
+	 */
+	nofs_flag = memalloc_nofs_save();
+	ret = kvzalloc(bitmap_rounded_size, GFP_KERNEL);
+	memalloc_nofs_restore(nofs_flag);
+	return ret;
+}
+
+static void le_bitmap_set(unsigned long *map, unsigned int start, int len)
+{
+	u8 *p = ((u8 *)map) + BIT_BYTE(start);
+	const unsigned int size = start + len;
+	int bits_to_set = BITS_PER_BYTE - (start % BITS_PER_BYTE);
+	u8 mask_to_set = BITMAP_FIRST_BYTE_MASK(start);
+
+	while (len - bits_to_set >= 0) {
+		*p |= mask_to_set;
+		len -= bits_to_set;
+		bits_to_set = BITS_PER_BYTE;
+		mask_to_set = ~0;
+		p++;
+	}
+	if (len) {
+		mask_to_set &= BITMAP_LAST_BYTE_MASK(size);
+		*p |= mask_to_set;
+	}
+}
+
+int convert_free_space_to_bitmaps(struct btrfs_trans_handle *trans,
+				  struct btrfs_block_group_cache *block_group,
+				  struct btrfs_path *path)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_root *root = fs_info->free_space_root;
+	struct btrfs_free_space_info *info;
+	struct btrfs_key key, found_key;
+	struct extent_buffer *leaf;
+	unsigned long *bitmap;
+	char *bitmap_cursor;
+	u64 start, end;
+	u64 bitmap_range, i;
+	u32 bitmap_size, flags, expected_extent_count;
+	u32 extent_count = 0;
+	int done = 0, nr;
+	int ret;
+
+	bitmap_size = free_space_bitmap_size(block_group->key.offset,
+					     fs_info->sectorsize);
+	bitmap = alloc_bitmap(bitmap_size);
+	if (!bitmap) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	start = block_group->key.objectid;
+	end = block_group->key.objectid + block_group->key.offset;
+
+	key.objectid = end - 1;
+	key.type = (u8)-1;
+	key.offset = (u64)-1;
+
+	while (!done) {
+		ret = btrfs_search_prev_slot(trans, root, &key, path, -1, 1);
+		if (ret)
+			goto out;
+
+		leaf = path->nodes[0];
+		nr = 0;
+		path->slots[0]++;
+		while (path->slots[0] > 0) {
+			btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0] - 1);
+
+			if (found_key.type == BTRFS_FREE_SPACE_INFO_KEY) {
+				ASSERT(found_key.objectid == block_group->key.objectid);
+				ASSERT(found_key.offset == block_group->key.offset);
+				done = 1;
+				break;
+			} else if (found_key.type == BTRFS_FREE_SPACE_EXTENT_KEY) {
+				u64 first, last;
+
+				ASSERT(found_key.objectid >= start);
+				ASSERT(found_key.objectid < end);
+				ASSERT(found_key.objectid + found_key.offset <= end);
+
+				first = div_u64(found_key.objectid - start,
+						fs_info->sectorsize);
+				last = div_u64(found_key.objectid + found_key.offset - start,
+					       fs_info->sectorsize);
+				le_bitmap_set(bitmap, first, last - first);
+
+				extent_count++;
+				nr++;
+				path->slots[0]--;
+			} else {
+				ASSERT(0);
+			}
+		}
+
+		ret = btrfs_del_items(trans, root, path, path->slots[0], nr);
+		if (ret)
+			goto out;
+		btrfs_release_path(path);
+	}
+
+	info = search_free_space_info(trans, fs_info, block_group, path, 1);
+	if (IS_ERR(info)) {
+		ret = PTR_ERR(info);
+		goto out;
+	}
+	leaf = path->nodes[0];
+	flags = btrfs_free_space_flags(leaf, info);
+	flags |= BTRFS_FREE_SPACE_USING_BITMAPS;
+	btrfs_set_free_space_flags(leaf, info, flags);
+	expected_extent_count = btrfs_free_space_extent_count(leaf, info);
+	btrfs_mark_buffer_dirty(leaf);
+	btrfs_release_path(path);
+
+	if (extent_count != expected_extent_count) {
+		fprintf(stderr,
+			"incorrect extent count for %llu; counted %u, expected %u",
+			block_group->key.objectid, extent_count,
+			expected_extent_count);
+		ASSERT(0);
+		ret = -EIO;
+		goto out;
+	}
+
+	bitmap_cursor = (char *)bitmap;
+	bitmap_range = fs_info->sectorsize * BTRFS_FREE_SPACE_BITMAP_BITS;
+	i = start;
+	while (i < end) {
+		unsigned long ptr;
+		u64 extent_size;
+		u32 data_size;
+
+		extent_size = min(end - i, bitmap_range);
+		data_size = free_space_bitmap_size(extent_size,
+						   fs_info->sectorsize);
+
+		key.objectid = i;
+		key.type = BTRFS_FREE_SPACE_BITMAP_KEY;
+		key.offset = extent_size;
+
+		ret = btrfs_insert_empty_item(trans, root, path, &key,
+					      data_size);
+		if (ret)
+			goto out;
+
+		leaf = path->nodes[0];
+		ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
+		write_extent_buffer(leaf, bitmap_cursor, ptr,
+				    data_size);
+		btrfs_mark_buffer_dirty(leaf);
+		btrfs_release_path(path);
+
+		i += extent_size;
+		bitmap_cursor += data_size;
+	}
+
+	ret = 0;
+out:
+	kvfree(bitmap);
+	if (ret)
+		btrfs_abort_transaction(trans, ret);
+	return ret;
+}
+
+int convert_free_space_to_extents(struct btrfs_trans_handle *trans,
+				  struct btrfs_block_group_cache *block_group,
+				  struct btrfs_path *path)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_root *root = fs_info->free_space_root;
+	struct btrfs_free_space_info *info;
+	struct btrfs_key key, found_key;
+	struct extent_buffer *leaf;
+	unsigned long *bitmap;
+	u64 start, end;
+	u32 bitmap_size, flags, expected_extent_count;
+	unsigned long nrbits, start_bit, end_bit;
+	u32 extent_count = 0;
+	int done = 0, nr;
+	int ret;
+
+	bitmap_size = free_space_bitmap_size(block_group->key.offset,
+					     fs_info->sectorsize);
+	bitmap = alloc_bitmap(bitmap_size);
+	if (!bitmap) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	start = block_group->key.objectid;
+	end = block_group->key.objectid + block_group->key.offset;
+
+	key.objectid = end - 1;
+	key.type = (u8)-1;
+	key.offset = (u64)-1;
+
+	while (!done) {
+		ret = btrfs_search_prev_slot(trans, root, &key, path, -1, 1);
+		if (ret)
+			goto out;
+
+		leaf = path->nodes[0];
+		nr = 0;
+		path->slots[0]++;
+		while (path->slots[0] > 0) {
+			btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0] - 1);
+
+			if (found_key.type == BTRFS_FREE_SPACE_INFO_KEY) {
+				ASSERT(found_key.objectid == block_group->key.objectid);
+				ASSERT(found_key.offset == block_group->key.offset);
+				done = 1;
+				break;
+			} else if (found_key.type == BTRFS_FREE_SPACE_BITMAP_KEY) {
+				unsigned long ptr;
+				char *bitmap_cursor;
+				u32 bitmap_pos, data_size;
+
+				ASSERT(found_key.objectid >= start);
+				ASSERT(found_key.objectid < end);
+				ASSERT(found_key.objectid + found_key.offset <= end);
+
+				bitmap_pos = div_u64(found_key.objectid - start,
+						     fs_info->sectorsize *
+						     BITS_PER_BYTE);
+				bitmap_cursor = ((char *)bitmap) + bitmap_pos;
+				data_size = free_space_bitmap_size(found_key.offset,
+								   fs_info->sectorsize);
+
+				ptr = btrfs_item_ptr_offset(leaf, path->slots[0] - 1);
+				read_extent_buffer(leaf, bitmap_cursor, ptr,
+						   data_size);
+
+				nr++;
+				path->slots[0]--;
+			} else {
+				ASSERT(0);
+			}
+		}
+
+		ret = btrfs_del_items(trans, root, path, path->slots[0], nr);
+		if (ret)
+			goto out;
+		btrfs_release_path(path);
+	}
+
+	info = search_free_space_info(trans, fs_info, block_group, path, 1);
+	if (IS_ERR(info)) {
+		ret = PTR_ERR(info);
+		goto out;
+	}
+	leaf = path->nodes[0];
+	flags = btrfs_free_space_flags(leaf, info);
+	flags &= ~BTRFS_FREE_SPACE_USING_BITMAPS;
+	btrfs_set_free_space_flags(leaf, info, flags);
+	expected_extent_count = btrfs_free_space_extent_count(leaf, info);
+	btrfs_mark_buffer_dirty(leaf);
+	btrfs_release_path(path);
+
+	nrbits = div_u64(block_group->key.offset, fs_info->sectorsize);
+	start_bit = find_next_bit_le(bitmap, nrbits, 0);
+
+	while (start_bit < nrbits) {
+		end_bit = find_next_zero_bit_le(bitmap, nrbits, start_bit);
+		ASSERT(start_bit < end_bit);
+
+		key.objectid = start + start_bit * fs_info->sectorsize;
+		key.type = BTRFS_FREE_SPACE_EXTENT_KEY;
+		key.offset = (end_bit - start_bit) * fs_info->sectorsize;
+
+		ret = btrfs_insert_empty_item(trans, root, path, &key, 0);
+		if (ret)
+			goto out;
+		btrfs_release_path(path);
+
+		extent_count++;
+
+		start_bit = find_next_bit_le(bitmap, nrbits, end_bit);
+	}
+
+	if (extent_count != expected_extent_count) {
+		fprintf(stderr,
+			"incorrect extent count for %llu; counted %u, expected %u",
+			block_group->key.objectid, extent_count,
+			expected_extent_count);
+		ASSERT(0);
+		ret = -EIO;
+		goto out;
+	}
+
+	ret = 0;
+out:
+	kvfree(bitmap);
+	if (ret)
+		btrfs_abort_transaction(trans, ret);
+	return ret;
+}
+
+static int update_free_space_extent_count(struct btrfs_trans_handle *trans,
+					  struct btrfs_block_group_cache *block_group,
+					  struct btrfs_path *path,
+					  int new_extents)
+{
+	struct btrfs_free_space_info *info;
+	u32 flags;
+	u32 extent_count;
+	int ret = 0;
+
+	if (new_extents == 0)
+		return 0;
+
+	info = search_free_space_info(trans, trans->fs_info, block_group, path,
+				1);
+	if (IS_ERR(info)) {
+		ret = PTR_ERR(info);
+		goto out;
+	}
+	flags = btrfs_free_space_flags(path->nodes[0], info);
+	extent_count = btrfs_free_space_extent_count(path->nodes[0], info);
+
+	extent_count += new_extents;
+	btrfs_set_free_space_extent_count(path->nodes[0], info, extent_count);
+	btrfs_mark_buffer_dirty(path->nodes[0]);
+	btrfs_release_path(path);
+
+	if (!(flags & BTRFS_FREE_SPACE_USING_BITMAPS) &&
+	    extent_count > block_group->bitmap_high_thresh) {
+		ret = convert_free_space_to_bitmaps(trans, block_group, path);
+	} else if ((flags & BTRFS_FREE_SPACE_USING_BITMAPS) &&
+		   extent_count < block_group->bitmap_low_thresh) {
+		ret = convert_free_space_to_extents(trans, block_group, path);
+	}
+
+
+out:
+	return ret;
+}
+
+
+static void free_space_set_bits(struct btrfs_block_group_cache *block_group,
+				struct btrfs_path *path, u64 *start, u64 *size,
+				int bit)
+{
+	struct extent_buffer *leaf = path->nodes[0];
+	struct btrfs_fs_info *fs_info = leaf->fs_info;
+	struct btrfs_key key;
+	u64 end = *start + *size;
+	u64 found_start, found_end;
+	unsigned long ptr, first, last;
+
+	btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
+	ASSERT(key.type == BTRFS_FREE_SPACE_BITMAP_KEY);
+
+	found_start = key.objectid;
+	found_end = key.objectid + key.offset;
+	ASSERT(*start >= found_start && *start < found_end);
+	ASSERT(end > found_start);
+
+	if (end > found_end)
+		end = found_end;
+
+	ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
+	first = (*start - found_start) / fs_info->sectorsize;
+	last = (end - found_start) / fs_info->sectorsize;
+	if (bit)
+		extent_buffer_bitmap_set(leaf, ptr, first, last - first);
+	else
+		extent_buffer_bitmap_clear(leaf, ptr, first, last - first);
+	btrfs_mark_buffer_dirty(leaf);
+
+	*size -= end - *start;
+	*start = end;
+}
+
+/*
+ * We can't use btrfs_next_item() in modify_free_space_bitmap() because
+ * btrfs_next_leaf() doesn't get the path for writing. We can forgo the fancy
+ * tree walking in btrfs_next_leaf() anyways because we know exactly what we're
+ * looking for.
+ */
+static int free_space_next_bitmap(struct btrfs_trans_handle *trans,
+				  struct btrfs_root *root, struct btrfs_path *p)
+{
+	struct btrfs_key key;
+
+	if (p->slots[0] + 1 < btrfs_header_nritems(p->nodes[0])) {
+		p->slots[0]++;
+		return 0;
+	}
+
+	btrfs_item_key_to_cpu(p->nodes[0], &key, p->slots[0]);
+	btrfs_release_path(p);
+
+	key.objectid += key.offset;
+	key.type = (u8)-1;
+	key.offset = (u64)-1;
+
+	return btrfs_search_prev_slot(trans, root, &key, p, 0, 1);
+}
+
+/*
+ * If remove is 1, then we are removing free space, thus clearing bits in the
+ * bitmap. If remove is 0, then we are adding free space, thus setting bits in
+ * the bitmap.
+ */
+static int modify_free_space_bitmap(struct btrfs_trans_handle *trans,
+				    struct btrfs_block_group_cache *block_group,
+				    struct btrfs_path *path,
+				    u64 start, u64 size, int remove)
+{
+	struct btrfs_root *root = trans->fs_info->free_space_root;
+	struct btrfs_key key;
+	u64 end = start + size;
+	u64 cur_start, cur_size;
+	int prev_bit, next_bit;
+	int new_extents;
+	int ret;
+
+	/*
+	 * Read the bit for the block immediately before the extent of space if
+	 * that block is within the block group.
+	 */
+	if (start > block_group->key.objectid) {
+		u64 prev_block = start - trans->fs_info->sectorsize;
+
+		key.objectid = prev_block;
+		key.type = (u8)-1;
+		key.offset = (u64)-1;
+
+		ret = btrfs_search_prev_slot(trans, root, &key, path, 0, 1);
+		if (ret)
+			goto out;
+
+		prev_bit = free_space_test_bit(block_group, path, prev_block);
+
+		/* The previous block may have been in the previous bitmap. */
+		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+		if (start >= key.objectid + key.offset) {
+			ret = free_space_next_bitmap(trans, root, path);
+			if (ret)
+				goto out;
+		}
+	} else {
+		key.objectid = start;
+		key.type = (u8)-1;
+		key.offset = (u64)-1;
+
+		ret = btrfs_search_prev_slot(trans, root, &key, path, 0, 1);
+		if (ret)
+			goto out;
+
+		prev_bit = -1;
+	}
+
+	/*
+	 * Iterate over all of the bitmaps overlapped by the extent of space,
+	 * clearing/setting bits as required.
+	 */
+	cur_start = start;
+	cur_size = size;
+	while (1) {
+		free_space_set_bits(block_group, path, &cur_start, &cur_size,
+					!remove);
+		if (cur_size == 0)
+			break;
+		ret = free_space_next_bitmap(trans, root, path);
+		if (ret)
+			goto out;
+	}
+
+	/*
+	 * Read the bit for the block immediately after the extent of space if
+	 * that block is within the block group.
+	 */
+	if (end < block_group->key.objectid + block_group->key.offset) {
+		/* The next block may be in the next bitmap. */
+		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+		if (end >= key.objectid + key.offset) {
+			ret = free_space_next_bitmap(trans, root, path);
+			if (ret)
+				goto out;
+		}
+
+		next_bit = free_space_test_bit(block_group, path, end);
+	} else {
+		next_bit = -1;
+	}
+
+	if (remove) {
+		new_extents = -1;
+		if (prev_bit == 1) {
+			/* Leftover on the left. */
+			new_extents++;
+		}
+		if (next_bit == 1) {
+			/* Leftover on the right. */
+			new_extents++;
+		}
+	} else {
+		new_extents = 1;
+		if (prev_bit == 1) {
+			/* Merging with neighbor on the left. */
+			new_extents--;
+		}
+		if (next_bit == 1) {
+			/* Merging with neighbor on the right. */
+			new_extents--;
+		}
+	}
+
+	btrfs_release_path(path);
+	ret = update_free_space_extent_count(trans, block_group, path,
+			new_extents);
+
+out:
+	return ret;
+}
+
+static int remove_free_space_extent(struct btrfs_trans_handle *trans,
+				    struct btrfs_block_group_cache *block_group,
+				    struct btrfs_path *path,
+				    u64 start, u64 size)
+{
+	struct btrfs_root *root = trans->fs_info->free_space_root;
+	struct btrfs_key key;
+	u64 found_start, found_end;
+	u64 end = start + size;
+	int new_extents = -1;
+	int ret;
+
+	key.objectid = start;
+	key.type = (u8)-1;
+	key.offset = (u64)-1;
+
+	ret = btrfs_search_prev_slot(trans, root, &key, path, -1, 1);
+	if (ret)
+		goto out;
+
+	btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+
+	ASSERT(key.type == BTRFS_FREE_SPACE_EXTENT_KEY);
+
+	found_start = key.objectid;
+	found_end = key.objectid + key.offset;
+	ASSERT(start >= found_start && end <= found_end);
+
+	/*
+	 * Okay, now that we've found the free space extent which contains the
+	 * free space that we are removing, there are four cases:
+	 *
+	 * 1. We're using the whole extent: delete the key we found and
+	 * decrement the free space extent count.
+	 * 2. We are using part of the extent starting at the beginning: delete
+	 * the key we found and insert a new key representing the leftover at
+	 * the end. There is no net change in the number of extents.
+	 * 3. We are using part of the extent ending at the end: delete the key
+	 * we found and insert a new key representing the leftover at the
+	 * beginning. There is no net change in the number of extents.
+	 * 4. We are using part of the extent in the middle: delete the key we
+	 * found and insert two new keys representing the leftovers on each
+	 * side. Where we used to have one extent, we now have two, so increment
+	 * the extent count. We may need to convert the block group to bitmaps
+	 * as a result.
+	 */
+
+	/* Delete the existing key (cases 1-4). */
+	ret = btrfs_del_item(trans, root, path);
+	if (ret)
+		goto out;
+
+	/* Add a key for leftovers at the beginning (cases 3 and 4). */
+	if (start > found_start) {
+		key.objectid = found_start;
+		key.type = BTRFS_FREE_SPACE_EXTENT_KEY;
+		key.offset = start - found_start;
+
+		btrfs_release_path(path);
+		ret = btrfs_insert_empty_item(trans, root, path, &key, 0);
+		if (ret)
+			goto out;
+		new_extents++;
+	}
+
+	/* Add a key for leftovers at the end (cases 2 and 4). */
+	if (end < found_end) {
+		key.objectid = end;
+		key.type = BTRFS_FREE_SPACE_EXTENT_KEY;
+		key.offset = found_end - end;
+
+		btrfs_release_path(path);
+		ret = btrfs_insert_empty_item(trans, root, path, &key, 0);
+		if (ret)
+			goto out;
+		new_extents++;
+	}
+
+	btrfs_release_path(path);
+	ret = update_free_space_extent_count(trans, block_group, path,
+					     new_extents);
+
+out:
+	return ret;
+}
+
+int __remove_from_free_space_tree(struct btrfs_trans_handle *trans,
+				  struct btrfs_block_group_cache *block_group,
+				  struct btrfs_path *path, u64 start, u64 size)
+{
+	struct btrfs_free_space_info *info;
+	u32 flags;
+
+	info = search_free_space_info(NULL, trans->fs_info, block_group, path, 0);
+	if (IS_ERR(info))
+		return PTR_ERR(info);
+	flags = btrfs_free_space_flags(path->nodes[0], info);
+	btrfs_release_path(path);
+
+	if (flags & BTRFS_FREE_SPACE_USING_BITMAPS) {
+		return modify_free_space_bitmap(trans, block_group, path,
+				start, size, 1);
+	} else {
+		return remove_free_space_extent(trans, block_group, path,
+				start, size);
+	}
+}
+
+int remove_from_free_space_tree(struct btrfs_trans_handle *trans, u64 start,
+		u64 size)
+{
+	struct btrfs_block_group_cache *block_group;
+	struct btrfs_path *path;
+	int ret;
+
+	if (!btrfs_fs_compat_ro(trans->fs_info, FREE_SPACE_TREE))
+		return 0;
+
+	path = btrfs_alloc_path();
+	if (!path) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	block_group = btrfs_lookup_block_group(trans->fs_info, start);
+	if (!block_group) {
+		ASSERT(0);
+		ret = -ENOENT;
+		goto out;
+	}
+
+	ret = __remove_from_free_space_tree(trans, block_group, path, start,
+					    size);
+out:
+	btrfs_free_path(path);
+	if (ret)
+		btrfs_abort_transaction(trans, ret);
+	return ret;
+}
+
+static int add_free_space_extent(struct btrfs_trans_handle *trans,
+				 struct btrfs_block_group_cache *block_group,
+				 struct btrfs_path *path,
+				 u64 start, u64 size)
+{
+	struct btrfs_root *root = trans->fs_info->free_space_root;
+	struct btrfs_key key, new_key;
+	u64 found_start, found_end;
+	u64 end = start + size;
+	int new_extents = 1;
+	int ret;
+
+	/*
+	 * We are adding a new extent of free space, but we need to merge
+	 * extents. There are four cases here:
+	 *
+	 * 1. The new extent does not have any immediate neighbors to merge
+	 * with: add the new key and increment the free space extent count. We
+	 * may need to convert the block group to bitmaps as a result.
+	 * 2. The new extent has an immediate neighbor before it: remove the
+	 * previous key and insert a new key combining both of them. There is no
+	 * net change in the number of extents.
+	 * 3. The new extent has an immediate neighbor after it: remove the next
+	 * key and insert a new key combining both of them. There is no net
+	 * change in the number of extents.
+	 * 4. The new extent has immediate neighbors on both sides: remove both
+	 * of the keys and insert a new key combining all of them. Where we used
+	 * to have two extents, we now have one, so decrement the extent count.
+	 */
+
+	new_key.objectid = start;
+	new_key.type = BTRFS_FREE_SPACE_EXTENT_KEY;
+	new_key.offset = size;
+
+	/* Search for a neighbor on the left. */
+	if (start == block_group->key.objectid)
+		goto right;
+	key.objectid = start - 1;
+	key.type = (u8)-1;
+	key.offset = (u64)-1;
+
+	ret = btrfs_search_prev_slot(trans, root, &key, path, -1, 1);
+	if (ret)
+		goto out;
+
+	btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+
+	if (key.type != BTRFS_FREE_SPACE_EXTENT_KEY) {
+		ASSERT(key.type == BTRFS_FREE_SPACE_INFO_KEY);
+		btrfs_release_path(path);
+		goto right;
+	}
+
+	found_start = key.objectid;
+	found_end = key.objectid + key.offset;
+	ASSERT(found_start >= block_group->key.objectid &&
+	       found_end > block_group->key.objectid);
+	ASSERT(found_start < start && found_end <= start);
+
+	/*
+	 * Delete the neighbor on the left and absorb it into the new key (cases
+	 * 2 and 4).
+	 */
+	if (found_end == start) {
+		ret = btrfs_del_item(trans, root, path);
+		if (ret)
+			goto out;
+		new_key.objectid = found_start;
+		new_key.offset += key.offset;
+		new_extents--;
+	}
+	btrfs_release_path(path);
+right:
+	/* Search for a neighbor on the right. */
+	if (end == block_group->key.objectid + block_group->key.offset)
+		goto insert;
+	key.objectid = end;
+	key.type = (u8)-1;
+	key.offset = (u64)-1;
+
+	ret = btrfs_search_prev_slot(trans, root, &key, path, -1, 1);
+	if (ret)
+		goto out;
+
+	btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+
+	if (key.type != BTRFS_FREE_SPACE_EXTENT_KEY) {
+		ASSERT(key.type == BTRFS_FREE_SPACE_INFO_KEY);
+		btrfs_release_path(path);
+		goto insert;
+	}
+
+	found_start = key.objectid;
+	found_end = key.objectid + key.offset;
+	ASSERT(found_start >= block_group->key.objectid &&
+			found_end > block_group->key.objectid);
+	ASSERT((found_start < start && found_end <= start) ||
+			(found_start >= end && found_end > end));
+
+	/*
+	 * Delete the neighbor on the right and absorb it into the new key
+	 * (cases 3 and 4).
+	 */
+	if (found_start == end) {
+		ret = btrfs_del_item(trans, root, path);
+		if (ret)
+			goto out;
+		new_key.offset += key.offset;
+		new_extents--;
+	}
+	btrfs_release_path(path);
+
+insert:
+	/* Insert the new key (cases 1-4). */
+	ret = btrfs_insert_empty_item(trans, root, path, &new_key, 0);
+	if (ret)
+		goto out;
+
+	btrfs_release_path(path);
+	ret = update_free_space_extent_count(trans, block_group, path,
+			new_extents);
+
+out:
+	return ret;
+}
+
+int __add_to_free_space_tree(struct btrfs_trans_handle *trans,
+			     struct btrfs_block_group_cache *block_group,
+			     struct btrfs_path *path, u64 start, u64 size)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_free_space_info *info;
+	u32 flags;
+
+	info = search_free_space_info(NULL, fs_info, block_group, path, 0);
+	if (IS_ERR(info))
+		return PTR_ERR(info);
+	flags = btrfs_free_space_flags(path->nodes[0], info);
+	btrfs_release_path(path);
+
+	if (flags & BTRFS_FREE_SPACE_USING_BITMAPS) {
+		return modify_free_space_bitmap(trans, block_group, path,
+				start, size, 0);
+	} else {
+		return add_free_space_extent(trans, block_group, path, start,
+				size);
+	}
+}
+
+int add_to_free_space_tree(struct btrfs_trans_handle *trans, u64 start,
+		u64 size)
+{
+	struct btrfs_block_group_cache *block_group;
+	struct btrfs_path *path;
+	int ret;
+
+	if (!btrfs_fs_compat_ro(trans->fs_info, FREE_SPACE_TREE))
+		return 0;
+
+	path = btrfs_alloc_path();
+	if (!path) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	block_group = btrfs_lookup_block_group(trans->fs_info, start);
+	if (!block_group) {
+		ASSERT(0);
+		ret = -ENOENT;
+		goto out;
+	}
+
+	ret = __add_to_free_space_tree(trans, block_group, path, start, size);
+out:
+	btrfs_free_path(path);
+	if (ret)
+		btrfs_abort_transaction(trans, ret);
+	return ret;
+}
+
+int populate_free_space_tree(struct btrfs_trans_handle *trans,
+			     struct btrfs_block_group_cache *block_group)
+{
+	struct btrfs_root *extent_root = trans->fs_info->extent_root;
+	struct btrfs_path *path, *path2;
+	struct btrfs_key key;
+	u64 start, end;
+	int ret;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+	path->reada = READA_FORWARD;
+
+	path2 = btrfs_alloc_path();
+	if (!path2) {
+		btrfs_free_path(path);
+		return -ENOMEM;
+	}
+
+	ret = add_new_free_space_info(trans, block_group, path2);
+	if (ret)
+		goto out;
+
+	/*
+	 * Iterate through all of the extent and metadata items in this block
+	 * group, adding the free space between them and the free space at the
+	 * end. Note that EXTENT_ITEM and METADATA_ITEM are less than
+	 * BLOCK_GROUP_ITEM, so an extent may precede the block group that it's
+	 * contained in.
+	 */
+	key.objectid = block_group->key.objectid;
+	key.type = BTRFS_EXTENT_ITEM_KEY;
+	key.offset = 0;
+
+	ret = btrfs_search_slot_for_read(extent_root, &key, path, 1, 0);
+	if (ret < 0)
+		goto out;
+	ASSERT(ret == 0);
+
+	start = block_group->key.objectid;
+	end = block_group->key.objectid + block_group->key.offset;
+	while (1) {
+		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+
+		if (key.type == BTRFS_EXTENT_ITEM_KEY ||
+				key.type == BTRFS_METADATA_ITEM_KEY) {
+			if (key.objectid >= end)
+				break;
+
+			if (start < key.objectid) {
+				ret = __add_to_free_space_tree(trans,
+						block_group, path2, start,
+						key.objectid - start);
+				if (ret)
+					goto out;
+			}
+			start = key.objectid;
+			if (key.type == BTRFS_METADATA_ITEM_KEY)
+				start += trans->fs_info->nodesize;
+			else
+				start += key.offset;
+		} else if (key.type == BTRFS_BLOCK_GROUP_ITEM_KEY) {
+			if (key.objectid != block_group->key.objectid)
+				break;
+		}
+
+		ret = btrfs_next_item(extent_root, path);
+		if (ret < 0)
+			goto out;
+		if (ret)
+			break;
+	}
+	if (start < end) {
+		ret = __add_to_free_space_tree(trans, block_group, path2,
+				start, end - start);
+		if (ret)
+			goto out;
+	}
+
+	ret = 0;
+out:
+	btrfs_free_path(path2);
+	btrfs_free_path(path);
+	return ret;
+}
+
+int remove_block_group_free_space(struct btrfs_trans_handle *trans,
+				  struct btrfs_block_group_cache *block_group)
+{
+	struct btrfs_root *root = trans->fs_info->free_space_root;
+	struct btrfs_path *path;
+	struct btrfs_key key, found_key;
+	struct extent_buffer *leaf;
+	u64 start, end;
+	int done = 0, nr;
+	int ret;
+
+	path = btrfs_alloc_path();
+	if (!path) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	start = block_group->key.objectid;
+	end = block_group->key.objectid + block_group->key.offset;
+
+	key.objectid = end - 1;
+	key.type = (u8)-1;
+	key.offset = (u64)-1;
+
+	while (!done) {
+		ret = btrfs_search_prev_slot(trans, root, &key, path, -1, 1);
+		if (ret)
+			goto out;
+
+		leaf = path->nodes[0];
+		nr = 0;
+		path->slots[0]++;
+		while (path->slots[0] > 0) {
+			btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0] - 1);
+
+			if (found_key.type == BTRFS_FREE_SPACE_INFO_KEY) {
+				ASSERT(found_key.objectid == block_group->key.objectid);
+				ASSERT(found_key.offset == block_group->key.offset);
+				done = 1;
+				nr++;
+				path->slots[0]--;
+				break;
+			} else if (found_key.type == BTRFS_FREE_SPACE_EXTENT_KEY ||
+				   found_key.type == BTRFS_FREE_SPACE_BITMAP_KEY) {
+				ASSERT(found_key.objectid >= start);
+				ASSERT(found_key.objectid < end);
+				ASSERT(found_key.objectid + found_key.offset <= end);
+				nr++;
+				path->slots[0]--;
+			} else {
+				ASSERT(0);
+			}
+		}
+
+		ret = btrfs_del_items(trans, root, path, path->slots[0], nr);
+		if (ret)
+			goto out;
+		btrfs_release_path(path);
+	}
+
+	ret = 0;
+out:
+	btrfs_free_path(path);
+	if (ret)
+		btrfs_abort_transaction(trans, ret);
+	return ret;
+}
 static int clear_free_space_tree(struct btrfs_trans_handle *trans,
 				 struct btrfs_root *root)
 {
@@ -204,8 +1304,8 @@ static int load_free_space_bitmaps(struct btrfs_fs_info *fs_info,
 
 		offset = key.objectid;
 		while (offset < key.objectid + key.offset) {
-			bit = free_space_test_bit(block_group, path, offset,
-						  fs_info->sectorsize);
+			bit = free_space_test_bit(block_group, path, offset);
+
 			if (prev_bit == 0 && bit == 1) {
 				extent_start = offset;
 			} else if (prev_bit == 1 && bit == 0) {
@@ -320,6 +1420,143 @@ out:
 	return ret;
 }
 
+struct btrfs_root *btrfs_create_tree(struct btrfs_trans_handle *trans,
+				     struct btrfs_fs_info *fs_info,
+				     u64 objectid)
+{
+	struct extent_buffer *leaf;
+	struct btrfs_root *tree_root = fs_info->tree_root;
+	struct btrfs_root *root;
+	struct btrfs_key key;
+	int ret = 0;
+
+	root = kzalloc(sizeof(*root), GFP_KERNEL);
+	if (!root)
+		return ERR_PTR(-ENOMEM);
+
+	btrfs_setup_root(root, fs_info, objectid);
+	root->root_key.objectid = objectid;
+	root->root_key.type = BTRFS_ROOT_ITEM_KEY;
+	root->root_key.offset = 0;
+
+	leaf = btrfs_alloc_free_block(trans, root, fs_info->nodesize, objectid,
+			NULL, 0, 0, 0);
+	if (IS_ERR(leaf)) {
+		ret = PTR_ERR(leaf);
+		leaf = NULL;
+		goto fail;
+	}
+
+	memset_extent_buffer(leaf, 0, 0, sizeof(struct btrfs_header));
+	btrfs_set_header_bytenr(leaf, leaf->start);
+	btrfs_set_header_generation(leaf, trans->transid);
+	btrfs_set_header_backref_rev(leaf, BTRFS_MIXED_BACKREF_REV);
+	btrfs_set_header_owner(leaf, objectid);
+	root->node = leaf;
+	write_extent_buffer(leaf, fs_info->fsid, btrfs_header_fsid(), BTRFS_FSID_SIZE);
+	write_extent_buffer(leaf, fs_info->chunk_tree_uuid,
+			    btrfs_header_chunk_tree_uuid(leaf),
+			    BTRFS_UUID_SIZE);
+	btrfs_mark_buffer_dirty(leaf);
+
+	extent_buffer_get(root->node);
+	root->commit_root = root->node;
+	root->track_dirty = 1;
+
+	root->root_item.flags = 0;
+	root->root_item.byte_limit = 0;
+	btrfs_set_root_bytenr(&root->root_item, leaf->start);
+	btrfs_set_root_generation(&root->root_item, trans->transid);
+	btrfs_set_root_level(&root->root_item, 0);
+	btrfs_set_root_refs(&root->root_item, 1);
+	btrfs_set_root_used(&root->root_item, leaf->len);
+	btrfs_set_root_last_snapshot(&root->root_item, 0);
+	btrfs_set_root_dirid(&root->root_item, 0);
+	memset(root->root_item.uuid, 0, BTRFS_UUID_SIZE);
+	root->root_item.drop_level = 0;
+
+	key.objectid = objectid;
+	key.type = BTRFS_ROOT_ITEM_KEY;
+	key.offset = 0;
+	ret = btrfs_insert_root(trans, tree_root, &key, &root->root_item);
+	if (ret)
+		goto fail;
+
+	return root;
+
+fail:
+	if (leaf)
+		free_extent_buffer(leaf);
+
+	kfree(root);
+	return ERR_PTR(ret);
+}
+
+#define btrfs_set_fs_compat_ro(__fs_info, opt) \
+	__btrfs_set_fs_compat_ro((__fs_info), BTRFS_FEATURE_COMPAT_RO_##opt)
+
+static inline void __btrfs_set_fs_compat_ro(struct btrfs_fs_info *fs_info,
+					    u64 flag)
+{
+	struct btrfs_super_block *disk_super;
+	u64 features;
+
+	disk_super = fs_info->super_copy;
+	features = btrfs_super_compat_ro_flags(disk_super);
+	if (!(features & flag)) {
+		features = btrfs_super_compat_ro_flags(disk_super);
+		if (!(features & flag)) {
+			features |= flag;
+			btrfs_set_super_compat_ro_flags(disk_super, features);
+		}
+	}
+}
+
+int btrfs_create_free_space_tree(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_trans_handle *trans;
+	struct btrfs_root *tree_root = fs_info->tree_root;
+	struct btrfs_root *free_space_root;
+	struct btrfs_block_group_cache *block_group;
+	u64 start = BTRFS_SUPER_INFO_OFFSET + BTRFS_SUPER_INFO_SIZE;
+	int ret;
+
+	trans = btrfs_start_transaction(tree_root, 0);
+	if (IS_ERR(trans))
+		return PTR_ERR(trans);
+
+	free_space_root = btrfs_create_tree(trans, fs_info,
+					    BTRFS_FREE_SPACE_TREE_OBJECTID);
+	if (IS_ERR(free_space_root)) {
+		ret = PTR_ERR(free_space_root);
+		goto abort;
+	}
+	fs_info->free_space_root = free_space_root;
+
+	do {
+		block_group = btrfs_lookup_first_block_group(fs_info, start);
+		if (!block_group)
+			break;
+		start = block_group->key.objectid + block_group->key.offset;
+		ret = populate_free_space_tree(trans, block_group);
+		if (ret)
+			goto abort;
+	} while (block_group);
+
+	btrfs_set_fs_compat_ro(fs_info, FREE_SPACE_TREE);
+	btrfs_set_fs_compat_ro(fs_info, FREE_SPACE_TREE_VALID);
+
+	ret = btrfs_commit_transaction(trans, tree_root);
+	if (ret)
+		return ret;
+
+	return 0;
+
+abort:
+	btrfs_abort_transaction(trans, ret);
+	return ret;
+}
+
 int load_free_space_tree(struct btrfs_fs_info *fs_info,
 			 struct btrfs_block_group_cache *block_group)
 {
@@ -332,7 +1569,7 @@ int load_free_space_tree(struct btrfs_fs_info *fs_info,
 	path = btrfs_alloc_path();
 	if (!path)
 		return -ENOMEM;
-	path->reada = 1;
+	path->reada = READA_BACK;
 
 	info = search_free_space_info(NULL, fs_info, block_group, path, 0);
 	if (IS_ERR(info)) {