btrfs: add tracing for failed reservations

When debugging ENOSPC issues, it's nice to be able to see which
reservations failed as well as the ones which succeeded.
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

fs/btrfs/extent-tree.c

@@ -3684,6 +3684,9 @@ int btrfs_check_data_free_space(struct inode *inode, u64 bytes)
 			goto again;
 		}
 
+		trace_btrfs_space_reservation(root->fs_info,
+					      "space_info:enospc",
+					      data_sinfo->flags, bytes, 1);
 		return -ENOSPC;
 	}
 	data_sinfo->bytes_may_use += bytes;
@@ -4335,6 +4338,10 @@ static int reserve_metadata_bytes(struct btrfs_root *root,
 		    !block_rsv_use_bytes(global_rsv, orig_bytes))
 			ret = 0;
 	}
+	if (ret == -ENOSPC)
+		trace_btrfs_space_reservation(root->fs_info,
+					      "space_info:enospc",
+					      space_info->flags, orig_bytes, 1);
 	if (flushing) {
 		spin_lock(&space_info->lock);
 		space_info->flush = 0;