btrfs-progs: add the ability to fix shifted item offsets

A user had a corrupted fs where the items had been shifted improperly.  This
patch adds the ability to fix this sort of problem within fsck.  We will simply
shift the item over to the proper offset and update the offsets to make sure
they are correct.  I tested this with a hand crafted fs that was broken in the
same way as the user, and I've included the file as a new test.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.cz>

cmds-check.c

@@ -2753,15 +2753,9 @@ static int swap_values(struct btrfs_root *root, struct btrfs_path *path,
 	return 0;
 }
 
-/*
- * Attempt to fix basic block failures.  Currently we only handle bad key
- * orders, we will cycle through the keys and swap them if necessary.
- */
-static int try_to_fix_bad_block(struct btrfs_trans_handle *trans,
-				struct btrfs_root *root,
-				struct extent_buffer *buf,
-				struct btrfs_disk_key *parent_key,
-				enum btrfs_tree_block_status status)
+static int fix_key_order(struct btrfs_trans_handle *trans,
+			 struct btrfs_root *root,
+			 struct extent_buffer *buf)
 {
 	struct btrfs_path *path;
 	struct btrfs_key k1, k2;
@@ -2769,9 +2763,6 @@ static int try_to_fix_bad_block(struct btrfs_trans_handle *trans,
 	int level;
 	int ret;
 
-	if (status != BTRFS_TREE_BLOCK_BAD_KEY_ORDER)
-		return -EIO;
-
 	k1.objectid = btrfs_header_owner(buf);
 	k1.type = BTRFS_ROOT_ITEM_KEY;
 	k1.offset = (u64)-1;
@@ -2822,6 +2813,111 @@ static int try_to_fix_bad_block(struct btrfs_trans_handle *trans,
 	return ret;
 }
 
+static int fix_item_offset(struct btrfs_trans_handle *trans,
+			   struct btrfs_root *root,
+			   struct extent_buffer *buf)
+{
+	struct btrfs_path *path;
+	struct btrfs_key k1;
+	int i;
+	int level;
+	int ret;
+
+	k1.objectid = btrfs_header_owner(buf);
+	k1.type = BTRFS_ROOT_ITEM_KEY;
+	k1.offset = (u64)-1;
+
+	root = btrfs_read_fs_root(root->fs_info, &k1);
+	if (IS_ERR(root))
+		return -EIO;
+
+	record_root_in_trans(trans, root);
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -EIO;
+
+	level = btrfs_header_level(buf);
+	path->lowest_level = level;
+	path->skip_check_block = 1;
+	if (level)
+		btrfs_node_key_to_cpu(buf, &k1, 0);
+	else
+		btrfs_item_key_to_cpu(buf, &k1, 0);
+
+	ret = btrfs_search_slot(trans, root, &k1, path, 0, 1);
+	if (ret) {
+		btrfs_free_path(path);
+		return -EIO;
+	}
+
+	buf = path->nodes[level];
+	for (i = 0; i < btrfs_header_nritems(buf); i++) {
+		unsigned int shift = 0, offset;
+
+		if (i == 0 && btrfs_item_end_nr(buf, i) !=
+		    BTRFS_LEAF_DATA_SIZE(root)) {
+			if (btrfs_item_end_nr(buf, i) >
+			    BTRFS_LEAF_DATA_SIZE(root)) {
+				fprintf(stderr, "item is off the end of the "
+					"leaf, can't fix\n");
+				ret = -EIO;
+				break;
+			}
+			shift = BTRFS_LEAF_DATA_SIZE(root) -
+				btrfs_item_end_nr(buf, i);
+		} else if (i > 0 && btrfs_item_end_nr(buf, i) !=
+			   btrfs_item_offset_nr(buf, i - 1)) {
+			if (btrfs_item_end_nr(buf, i) >
+			    btrfs_item_offset_nr(buf, i - 1)) {
+				fprintf(stderr, "items overlap, can't fix\n");
+				ret = -EIO;
+				break;
+			}
+			shift = btrfs_item_offset_nr(buf, i - 1) -
+				btrfs_item_end_nr(buf, i);
+		}
+		if (!shift)
+			continue;
+
+		printf("Shifting item nr %d by %u bytes in block %llu\n",
+		       i, shift, (unsigned long long)buf->start);
+		offset = btrfs_item_offset_nr(buf, i);
+		memmove_extent_buffer(buf,
+				      btrfs_leaf_data(buf) + offset + shift,
+				      btrfs_leaf_data(buf) + offset,
+				      btrfs_item_size_nr(buf, i));
+		btrfs_set_item_offset(buf, btrfs_item_nr(i),
+				      offset + shift);
+		btrfs_mark_buffer_dirty(buf);
+	}
+
+	/*
+	 * We may have moved things, in which case we want to exit so we don't
+	 * write those changes out.  Once we have proper abort functionality in
+	 * progs this can be changed to something nicer.
+	 */
+	BUG_ON(ret);
+	btrfs_free_path(path);
+	return ret;
+}
+
+/*
+ * Attempt to fix basic block failures.  If we can't fix it for whatever reason
+ * then just return -EIO.
+ */
+static int try_to_fix_bad_block(struct btrfs_trans_handle *trans,
+				struct btrfs_root *root,
+				struct extent_buffer *buf,
+				enum btrfs_tree_block_status status)
+{
+	if (status == BTRFS_TREE_BLOCK_BAD_KEY_ORDER)
+		return fix_key_order(trans, root, buf);
+	if (status == BTRFS_TREE_BLOCK_INVALID_OFFSETS)
+		return fix_item_offset(trans, root, buf);
+	return -EIO;
+}
+
 static int check_block(struct btrfs_trans_handle *trans,
 		       struct btrfs_root *root,
 		       struct cache_tree *extent_cache,
@@ -2860,7 +2956,6 @@ static int check_block(struct btrfs_trans_handle *trans,
 	if (status != BTRFS_TREE_BLOCK_CLEAN) {
 		if (repair)
 			status = try_to_fix_bad_block(trans, root, buf,
-						      &rec->parent_key,
 						      status);
 		if (status != BTRFS_TREE_BLOCK_CLEAN) {
 			ret = -EIO;