Btrfs: remove dead code

This patch removes a bunch of dead code from the snapshot removal stuff.  It
was confusing me when doing the metadata ENOSPC stuff so I killed it.

Signed-off-by: Josef Bacik <jbacik@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 0 insertions, 706 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 0f41da2..93e376a 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4462,430 +4462,6 @@ struct extent_buffer *btrfs_alloc_free_block(struct btrfs_trans_handle *trans,
 	return buf;
 }
 
-#if 0
-int btrfs_drop_leaf_ref(struct btrfs_trans_handle *trans,
-			struct btrfs_root *root, struct extent_buffer *leaf)
-{
-	u64 disk_bytenr;
-	u64 num_bytes;
-	struct btrfs_key key;
-	struct btrfs_file_extent_item *fi;
-	u32 nritems;
-	int i;
-	int ret;
-
-	BUG_ON(!btrfs_is_leaf(leaf));
-	nritems = btrfs_header_nritems(leaf);
-
-	for (i = 0; i < nritems; i++) {
-		cond_resched();
-		btrfs_item_key_to_cpu(leaf, &key, i);
-
-		/* only extents have references, skip everything else */
-		if (btrfs_key_type(&key) != BTRFS_EXTENT_DATA_KEY)
-			continue;
-
-		fi = btrfs_item_ptr(leaf, i, struct btrfs_file_extent_item);
-
-		/* inline extents live in the btree, they don't have refs */
-		if (btrfs_file_extent_type(leaf, fi) ==
-		    BTRFS_FILE_EXTENT_INLINE)
-			continue;
-
-		disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
-
-		/* holes don't have refs */
-		if (disk_bytenr == 0)
-			continue;
-
-		num_bytes = btrfs_file_extent_disk_num_bytes(leaf, fi);
-		ret = btrfs_free_extent(trans, root, disk_bytenr, num_bytes,
-					leaf->start, 0, key.objectid, 0);
-		BUG_ON(ret);
-	}
-	return 0;
-}
-
-static noinline int cache_drop_leaf_ref(struct btrfs_trans_handle *trans,
-					struct btrfs_root *root,
-					struct btrfs_leaf_ref *ref)
-{
-	int i;
-	int ret;
-	struct btrfs_extent_info *info;
-	struct refsort *sorted;
-
-	if (ref->nritems == 0)
-		return 0;
-
-	sorted = kmalloc(sizeof(*sorted) * ref->nritems, GFP_NOFS);
-	for (i = 0; i < ref->nritems; i++) {
-		sorted[i].bytenr = ref->extents[i].bytenr;
-		sorted[i].slot = i;
-	}
-	sort(sorted, ref->nritems, sizeof(struct refsort), refsort_cmp, NULL);
-
-	/*
-	 * the items in the ref were sorted when the ref was inserted
-	 * into the ref cache, so this is already in order
-	 */
-	for (i = 0; i < ref->nritems; i++) {
-		info = ref->extents + sorted[i].slot;
-		ret = btrfs_free_extent(trans, root, info->bytenr,
-					  info->num_bytes, ref->bytenr,
-					  ref->owner, ref->generation,
-					  info->objectid, 0);
-
-		atomic_inc(&root->fs_info->throttle_gen);
-		wake_up(&root->fs_info->transaction_throttle);
-		cond_resched();
-
-		BUG_ON(ret);
-		info++;
-	}
-
-	kfree(sorted);
-	return 0;
-}
-
-
-static int drop_snap_lookup_refcount(struct btrfs_trans_handle *trans,
-				     struct btrfs_root *root, u64 start,
-				     u64 len, u32 *refs)
-{
-	int ret;
-
-	ret = btrfs_lookup_extent_refs(trans, root, start, len, refs);
-	BUG_ON(ret);
-
-#if 0 /* some debugging code in case we see problems here */
-	/* if the refs count is one, it won't get increased again.  But
-	 * if the ref count is > 1, someone may be decreasing it at
-	 * the same time we are.
-	 */
-	if (*refs != 1) {
-		struct extent_buffer *eb = NULL;
-		eb = btrfs_find_create_tree_block(root, start, len);
-		if (eb)
-			btrfs_tree_lock(eb);
-
-		mutex_lock(&root->fs_info->alloc_mutex);
-		ret = lookup_extent_ref(NULL, root, start, len, refs);
-		BUG_ON(ret);
-		mutex_unlock(&root->fs_info->alloc_mutex);
-
-		if (eb) {
-			btrfs_tree_unlock(eb);
-			free_extent_buffer(eb);
-		}
-		if (*refs == 1) {
-			printk(KERN_ERR "btrfs block %llu went down to one "
-			       "during drop_snap\n", (unsigned long long)start);
-		}
-
-	}
-#endif
-
-	cond_resched();
-	return ret;
-}
-
-
-/*
- * this is used while deleting old snapshots, and it drops the refs
- * on a whole subtree starting from a level 1 node.
- *
- * The idea is to sort all the leaf pointers, and then drop the
- * ref on all the leaves in order.  Most of the time the leaves
- * will have ref cache entries, so no leaf IOs will be required to
- * find the extents they have references on.
- *
- * For each leaf, any references it has are also dropped in order
- *
- * This ends up dropping the references in something close to optimal
- * order for reading and modifying the extent allocation tree.
- */
-static noinline int drop_level_one_refs(struct btrfs_trans_handle *trans,
-					struct btrfs_root *root,
-					struct btrfs_path *path)
-{
-	u64 bytenr;
-	u64 root_owner;
-	u64 root_gen;
-	struct extent_buffer *eb = path->nodes[1];
-	struct extent_buffer *leaf;
-	struct btrfs_leaf_ref *ref;
-	struct refsort *sorted = NULL;
-	int nritems = btrfs_header_nritems(eb);
-	int ret;
-	int i;
-	int refi = 0;
-	int slot = path->slots[1];
-	u32 blocksize = btrfs_level_size(root, 0);
-	u32 refs;
-
-	if (nritems == 0)
-		goto out;
-
-	root_owner = btrfs_header_owner(eb);
-	root_gen = btrfs_header_generation(eb);
-	sorted = kmalloc(sizeof(*sorted) * nritems, GFP_NOFS);
-
-	/*
-	 * step one, sort all the leaf pointers so we don't scribble
-	 * randomly into the extent allocation tree
-	 */
-	for (i = slot; i < nritems; i++) {
-		sorted[refi].bytenr = btrfs_node_blockptr(eb, i);
-		sorted[refi].slot = i;
-		refi++;
-	}
-
-	/*
-	 * nritems won't be zero, but if we're picking up drop_snapshot
-	 * after a crash, slot might be > 0, so double check things
-	 * just in case.
-	 */
-	if (refi == 0)
-		goto out;
-
-	sort(sorted, refi, sizeof(struct refsort), refsort_cmp, NULL);
-
-	/*
-	 * the first loop frees everything the leaves point to
-	 */
-	for (i = 0; i < refi; i++) {
-		u64 ptr_gen;
-
-		bytenr = sorted[i].bytenr;
-
-		/*
-		 * check the reference count on this leaf.  If it is > 1
-		 * we just decrement it below and don't update any
-		 * of the refs the leaf points to.
-		 */
-		ret = drop_snap_lookup_refcount(trans, root, bytenr,
-						blocksize, &refs);
-		BUG_ON(ret);
-		if (refs != 1)
-			continue;
-
-		ptr_gen = btrfs_node_ptr_generation(eb, sorted[i].slot);
-
-		/*
-		 * the leaf only had one reference, which means the
-		 * only thing pointing to this leaf is the snapshot
-		 * we're deleting.  It isn't possible for the reference
-		 * count to increase again later
-		 *
-		 * The reference cache is checked for the leaf,
-		 * and if found we'll be able to drop any refs held by
-		 * the leaf without needing to read it in.
-		 */
-		ref = btrfs_lookup_leaf_ref(root, bytenr);
-		if (ref && ref->generation != ptr_gen) {
-			btrfs_free_leaf_ref(root, ref);
-			ref = NULL;
-		}
-		if (ref) {
-			ret = cache_drop_leaf_ref(trans, root, ref);
-			BUG_ON(ret);
-			btrfs_remove_leaf_ref(root, ref);
-			btrfs_free_leaf_ref(root, ref);
-		} else {
-			/*
-			 * the leaf wasn't in the reference cache, so
-			 * we have to read it.
-			 */
-			leaf = read_tree_block(root, bytenr, blocksize,
-					       ptr_gen);
-			ret = btrfs_drop_leaf_ref(trans, root, leaf);
-			BUG_ON(ret);
-			free_extent_buffer(leaf);
-		}
-		atomic_inc(&root->fs_info->throttle_gen);
-		wake_up(&root->fs_info->transaction_throttle);
-		cond_resched();
-	}
-
-	/*
-	 * run through the loop again to free the refs on the leaves.
-	 * This is faster than doing it in the loop above because
-	 * the leaves are likely to be clustered together.  We end up
-	 * working in nice chunks on the extent allocation tree.
-	 */
-	for (i = 0; i < refi; i++) {
-		bytenr = sorted[i].bytenr;
-		ret = btrfs_free_extent(trans, root, bytenr,
-					blocksize, eb->start,
-					root_owner, root_gen, 0, 1);
-		BUG_ON(ret);
-
-		atomic_inc(&root->fs_info->throttle_gen);
-		wake_up(&root->fs_info->transaction_throttle);
-		cond_resched();
-	}
-out:
-	kfree(sorted);
-
-	/*
-	 * update the path to show we've processed the entire level 1
-	 * node.  This will get saved into the root's drop_snapshot_progress
-	 * field so these drops are not repeated again if this transaction
-	 * commits.
-	 */
-	path->slots[1] = nritems;
-	return 0;
-}
-
-/*
- * helper function for drop_snapshot, this walks down the tree dropping ref
- * counts as it goes.
- */
-static noinline int walk_down_tree(struct btrfs_trans_handle *trans,
-				   struct btrfs_root *root,
-				   struct btrfs_path *path, int *level)
-{
-	u64 root_owner;
-	u64 root_gen;
-	u64 bytenr;
-	u64 ptr_gen;
-	struct extent_buffer *next;
-	struct extent_buffer *cur;
-	struct extent_buffer *parent;
-	u32 blocksize;
-	int ret;
-	u32 refs;
-
-	WARN_ON(*level < 0);
-	WARN_ON(*level >= BTRFS_MAX_LEVEL);
-	ret = drop_snap_lookup_refcount(trans, root, path->nodes[*level]->start,
-				path->nodes[*level]->len, &refs);
-	BUG_ON(ret);
-	if (refs > 1)
-		goto out;
-
-	/*
-	 * walk down to the last node level and free all the leaves
-	 */
-	while (*level >= 0) {
-		WARN_ON(*level < 0);
-		WARN_ON(*level >= BTRFS_MAX_LEVEL);
-		cur = path->nodes[*level];
-
-		if (btrfs_header_level(cur) != *level)
-			WARN_ON(1);
-
-		if (path->slots[*level] >=
-		    btrfs_header_nritems(cur))
-			break;
-
-		/* the new code goes down to level 1 and does all the
-		 * leaves pointed to that node in bulk.  So, this check
-		 * for level 0 will always be false.
-		 *
-		 * But, the disk format allows the drop_snapshot_progress
-		 * field in the root to leave things in a state where
-		 * a leaf will need cleaning up here.  If someone crashes
-		 * with the old code and then boots with the new code,
-		 * we might find a leaf here.
-		 */
-		if (*level == 0) {
-			ret = btrfs_drop_leaf_ref(trans, root, cur);
-			BUG_ON(ret);
-			break;
-		}
-
-		/*
-		 * once we get to level one, process the whole node
-		 * at once, including everything below it.
-		 */
-		if (*level == 1) {
-			ret = drop_level_one_refs(trans, root, path);
-			BUG_ON(ret);
-			break;
-		}
-
-		bytenr = btrfs_node_blockptr(cur, path->slots[*level]);
-		ptr_gen = btrfs_node_ptr_generation(cur, path->slots[*level]);
-		blocksize = btrfs_level_size(root, *level - 1);
-
-		ret = drop_snap_lookup_refcount(trans, root, bytenr,
-						blocksize, &refs);
-		BUG_ON(ret);
-
-		/*
-		 * if there is more than one reference, we don't need
-		 * to read that node to drop any references it has.  We
-		 * just drop the ref we hold on that node and move on to the
-		 * next slot in this level.
-		 */
-		if (refs != 1) {
-			parent = path->nodes[*level];
-			root_owner = btrfs_header_owner(parent);
-			root_gen = btrfs_header_generation(parent);
-			path->slots[*level]++;
-
-			ret = btrfs_free_extent(trans, root, bytenr,
-						blocksize, parent->start,
-						root_owner, root_gen,
-						*level - 1, 1);
-			BUG_ON(ret);
-
-			atomic_inc(&root->fs_info->throttle_gen);
-			wake_up(&root->fs_info->transaction_throttle);
-			cond_resched();
-
-			continue;
-		}
-
-		/*
-		 * we need to keep freeing things in the next level down.
-		 * read the block and loop around to process it
-		 */
-		next = read_tree_block(root, bytenr, blocksize, ptr_gen);
-		WARN_ON(*level <= 0);
-		if (path->nodes[*level-1])
-			free_extent_buffer(path->nodes[*level-1]);
-		path->nodes[*level-1] = next;
-		*level = btrfs_header_level(next);
-		path->slots[*level] = 0;
-		cond_resched();
-	}
-out:
-	WARN_ON(*level < 0);
-	WARN_ON(*level >= BTRFS_MAX_LEVEL);
-
-	if (path->nodes[*level] == root->node) {
-		parent = path->nodes[*level];
-		bytenr = path->nodes[*level]->start;
-	} else {
-		parent = path->nodes[*level + 1];
-		bytenr = btrfs_node_blockptr(parent, path->slots[*level + 1]);
-	}
-
-	blocksize = btrfs_level_size(root, *level);
-	root_owner = btrfs_header_owner(parent);
-	root_gen = btrfs_header_generation(parent);
-
-	/*
-	 * cleanup and free the reference on the last node
-	 * we processed
-	 */
-	ret = btrfs_free_extent(trans, root, bytenr, blocksize,
-				  parent->start, root_owner, root_gen,
-				  *level, 1);
-	free_extent_buffer(path->nodes[*level]);
-	path->nodes[*level] = NULL;
-
-	*level += 1;
-	BUG_ON(ret);
-
-	cond_resched();
-	return 0;
-}
-#endif
-
 struct walk_control {
 	u64 refs[BTRFS_MAX_LEVEL];
 	u64 flags[BTRFS_MAX_LEVEL];
@@ -7129,288 +6705,6 @@ int btrfs_prepare_block_group_relocation(struct btrfs_root *root,
 	return 0;
 }
 
-#if 0
-static int __insert_orphan_inode(struct btrfs_trans_handle *trans,
-				 struct btrfs_root *root,
-				 u64 objectid, u64 size)
-{
-	struct btrfs_path *path;
-	struct btrfs_inode_item *item;
-	struct extent_buffer *leaf;
-	int ret;
-
-	path = btrfs_alloc_path();
-	if (!path)
-		return -ENOMEM;
-
-	path->leave_spinning = 1;
-	ret = btrfs_insert_empty_inode(trans, root, path, objectid);
-	if (ret)
-		goto out;
-
-	leaf = path->nodes[0];
-	item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_inode_item);
-	memset_extent_buffer(leaf, 0, (unsigned long)item, sizeof(*item));
-	btrfs_set_inode_generation(leaf, item, 1);
-	btrfs_set_inode_size(leaf, item, size);
-	btrfs_set_inode_mode(leaf, item, S_IFREG | 0600);
-	btrfs_set_inode_flags(leaf, item, BTRFS_INODE_NOCOMPRESS);
-	btrfs_mark_buffer_dirty(leaf);
-	btrfs_release_path(root, path);
-out:
-	btrfs_free_path(path);
-	return ret;
-}
-
-static noinline struct inode *create_reloc_inode(struct btrfs_fs_info *fs_info,
-					struct btrfs_block_group_cache *group)
-{
-	struct inode *inode = NULL;
-	struct btrfs_trans_handle *trans;
-	struct btrfs_root *root;
-	struct btrfs_key root_key;
-	u64 objectid = BTRFS_FIRST_FREE_OBJECTID;
-	int err = 0;
-
-	root_key.objectid = BTRFS_DATA_RELOC_TREE_OBJECTID;
-	root_key.type = BTRFS_ROOT_ITEM_KEY;
-	root_key.offset = (u64)-1;
-	root = btrfs_read_fs_root_no_name(fs_info, &root_key);
-	if (IS_ERR(root))
-		return ERR_CAST(root);
-
-	trans = btrfs_start_transaction(root, 1);
-	BUG_ON(!trans);
-
-	err = btrfs_find_free_objectid(trans, root, objectid, &objectid);
-	if (err)
-		goto out;
-
-	err = __insert_orphan_inode(trans, root, objectid, group->key.offset);
-	BUG_ON(err);
-
-	err = btrfs_insert_file_extent(trans, root, objectid, 0, 0, 0,
-				       group->key.offset, 0, group->key.offset,
-				       0, 0, 0);
-	BUG_ON(err);
-
-	inode = btrfs_iget_locked(root->fs_info->sb, objectid, root);
-	if (inode->i_state & I_NEW) {
-		BTRFS_I(inode)->root = root;
-		BTRFS_I(inode)->location.objectid = objectid;
-		BTRFS_I(inode)->location.type = BTRFS_INODE_ITEM_KEY;
-		BTRFS_I(inode)->location.offset = 0;
-		btrfs_read_locked_inode(inode);
-		unlock_new_inode(inode);
-		BUG_ON(is_bad_inode(inode));
-	} else {
-		BUG_ON(1);
-	}
-	BTRFS_I(inode)->index_cnt = group->key.objectid;
-
-	err = btrfs_orphan_add(trans, inode);
-out:
-	btrfs_end_transaction(trans, root);
-	if (err) {
-		if (inode)
-			iput(inode);
-		inode = ERR_PTR(err);
-	}
-	return inode;
-}
-
-int btrfs_reloc_clone_csums(struct inode *inode, u64 file_pos, u64 len)
-{
-
-	struct btrfs_ordered_sum *sums;
-	struct btrfs_sector_sum *sector_sum;
-	struct btrfs_ordered_extent *ordered;
-	struct btrfs_root *root = BTRFS_I(inode)->root;
-	struct list_head list;
-	size_t offset;
-	int ret;
-	u64 disk_bytenr;
-
-	INIT_LIST_HEAD(&list);
-
-	ordered = btrfs_lookup_ordered_extent(inode, file_pos);
-	BUG_ON(ordered->file_offset != file_pos || ordered->len != len);
-
-	disk_bytenr = file_pos + BTRFS_I(inode)->index_cnt;
-	ret = btrfs_lookup_csums_range(root->fs_info->csum_root, disk_bytenr,
-				       disk_bytenr + len - 1, &list);
-
-	while (!list_empty(&list)) {
-		sums = list_entry(list.next, struct btrfs_ordered_sum, list);
-		list_del_init(&sums->list);
-
-		sector_sum = sums->sums;
-		sums->bytenr = ordered->start;
-
-		offset = 0;
-		while (offset < sums->len) {
-			sector_sum->bytenr += ordered->start - disk_bytenr;
-			sector_sum++;
-			offset += root->sectorsize;
-		}
-
-		btrfs_add_ordered_sum(inode, ordered, sums);
-	}
-	btrfs_put_ordered_extent(ordered);
-	return 0;
-}
-
-int btrfs_relocate_block_group(struct btrfs_root *root, u64 group_start)
-{
-	struct btrfs_trans_handle *trans;
-	struct btrfs_path *path;
-	struct btrfs_fs_info *info = root->fs_info;
-	struct extent_buffer *leaf;
-	struct inode *reloc_inode;
-	struct btrfs_block_group_cache *block_group;
-	struct btrfs_key key;
-	u64 skipped;
-	u64 cur_byte;
-	u64 total_found;
-	u32 nritems;
-	int ret;
-	int progress;
-	int pass = 0;
-
-	root = root->fs_info->extent_root;
-
-	block_group = btrfs_lookup_block_group(info, group_start);
-	BUG_ON(!block_group);
-
-	printk(KERN_INFO "btrfs relocating block group %llu flags %llu\n",
-	       (unsigned long long)block_group->key.objectid,
-	       (unsigned long long)block_group->flags);
-
-	path = btrfs_alloc_path();
-	BUG_ON(!path);
-
-	reloc_inode = create_reloc_inode(info, block_group);
-	BUG_ON(IS_ERR(reloc_inode));
-
-	__alloc_chunk_for_shrink(root, block_group, 1);
-	set_block_group_readonly(block_group);
-
-	btrfs_start_delalloc_inodes(info->tree_root);
-	btrfs_wait_ordered_extents(info->tree_root, 0);
-again:
-	skipped = 0;
-	total_found = 0;
-	progress = 0;
-	key.objectid = block_group->key.objectid;
-	key.offset = 0;
-	key.type = 0;
-	cur_byte = key.objectid;
-
-	trans = btrfs_start_transaction(info->tree_root, 1);
-	btrfs_commit_transaction(trans, info->tree_root);
-
-	mutex_lock(&root->fs_info->cleaner_mutex);
-	btrfs_clean_old_snapshots(info->tree_root);
-	btrfs_remove_leaf_refs(info->tree_root, (u64)-1, 1);
-	mutex_unlock(&root->fs_info->cleaner_mutex);
-
-	trans = btrfs_start_transaction(info->tree_root, 1);
-	btrfs_commit_transaction(trans, info->tree_root);
-
-	while (1) {
-		ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
-		if (ret < 0)
-			goto out;
-next:
-		leaf = path->nodes[0];
-		nritems = btrfs_header_nritems(leaf);
-		if (path->slots[0] >= nritems) {
-			ret = btrfs_next_leaf(root, path);
-			if (ret < 0)
-				goto out;
-			if (ret == 1) {
-				ret = 0;
-				break;
-			}
-			leaf = path->nodes[0];
-			nritems = btrfs_header_nritems(leaf);
-		}
-
-		btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
-
-		if (key.objectid >= block_group->key.objectid +
-		    block_group->key.offset)
-			break;
-
-		if (progress && need_resched()) {
-			btrfs_release_path(root, path);
-			cond_resched();
-			progress = 0;
-			continue;
-		}
-		progress = 1;
-
-		if (btrfs_key_type(&key) != BTRFS_EXTENT_ITEM_KEY ||
-		    key.objectid + key.offset <= cur_byte) {
-			path->slots[0]++;
-			goto next;
-		}
-
-		total_found++;
-		cur_byte = key.objectid + key.offset;
-		btrfs_release_path(root, path);
-
-		__alloc_chunk_for_shrink(root, block_group, 0);
-		ret = relocate_one_extent(root, path, &key, block_group,
-					  reloc_inode, pass);
-		BUG_ON(ret < 0);
-		if (ret > 0)
-			skipped++;
-
-		key.objectid = cur_byte;
-		key.type = 0;
-		key.offset = 0;
-	}
-
-	btrfs_release_path(root, path);
-
-	if (pass == 0) {
-		btrfs_wait_ordered_range(reloc_inode, 0, (u64)-1);
-		invalidate_mapping_pages(reloc_inode->i_mapping, 0, -1);
-	}
-
-	if (total_found > 0) {
-		printk(KERN_INFO "btrfs found %llu extents in pass %d\n",
-		       (unsigned long long)total_found, pass);
-		pass++;
-		if (total_found == skipped && pass > 2) {
-			iput(reloc_inode);
-			reloc_inode = create_reloc_inode(info, block_group);
-			pass = 0;
-		}
-		goto again;
-	}
-
-	/* delete reloc_inode */
-	iput(reloc_inode);
-
-	/* unpin extents in this range */
-	trans = btrfs_start_transaction(info->tree_root, 1);
-	btrfs_commit_transaction(trans, info->tree_root);
-
-	spin_lock(&block_group->lock);
-	WARN_ON(block_group->pinned > 0);
-	WARN_ON(block_group->reserved > 0);
-	WARN_ON(btrfs_block_group_used(&block_group->item) > 0);
-	spin_unlock(&block_group->lock);
-	btrfs_put_block_group(block_group);
-	ret = 0;
-out:
-	btrfs_free_path(path);
-	return ret;
-}
-#endif
-
 /*
  * checks to see if its even possible to relocate this block group.
  *