Btrfs: faster file extent item search in clone ioctl

When we are looking for file extent items that intersect the cloning
range, for each one that falls completely outside the range, don't
release the path and do another full tree search - just move on
to the next slot and copy the file extent item into our buffer only
if the item intersects the cloning range.

Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 5ed5bd0..829999d 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2905,12 +2905,14 @@
 		 * note the key will change type as we walk through the
 		 * tree.
 		 */
+		path->leave_spinning = 1;
 		ret = btrfs_search_slot(NULL, BTRFS_I(src)->root, &key, path,
 				0, 0);
 		if (ret < 0)
 			goto out;
 
 		nritems = btrfs_header_nritems(path->nodes[0]);
+process_slot:
 		if (path->slots[0] >= nritems) {
 			ret = btrfs_next_leaf(BTRFS_I(src)->root, path);
 			if (ret < 0)
@@ -2937,11 +2939,6 @@
 			u8 comp;
 			u64 endoff;
 
-			size = btrfs_item_size_nr(leaf, slot);
-			read_extent_buffer(leaf, buf,
-					   btrfs_item_ptr_offset(leaf, slot),
-					   size);
-
 			extent = btrfs_item_ptr(leaf, slot,
 						struct btrfs_file_extent_item);
 			comp = btrfs_file_extent_compression(leaf, extent);
@@ -2960,11 +2957,20 @@
 				datal = btrfs_file_extent_ram_bytes(leaf,
 								    extent);
 			}
-			btrfs_release_path(path);
 
 			if (key.offset + datal <= off ||
-			    key.offset >= off + len - 1)
-				goto next;
+			    key.offset >= off + len - 1) {
+				path->slots[0]++;
+				goto process_slot;
+			}
+
+			size = btrfs_item_size_nr(leaf, slot);
+			read_extent_buffer(leaf, buf,
+					   btrfs_item_ptr_offset(leaf, slot),
+					   size);
+
+			btrfs_release_path(path);
+			path->leave_spinning = 0;
 
 			memcpy(&new_key, &key, sizeof(new_key));
 			new_key.objectid = btrfs_ino(inode);
@@ -3135,7 +3141,6 @@
 			}
 			ret = btrfs_end_transaction(trans, root);
 		}
-next:
 		btrfs_release_path(path);
 		key.offset++;
 	}