btrfs: retrieve more info from FS_INFO ioctl

Provide the basic information about filesystem through the ioctl:
* b-tree node size (same as leaf size)
* sector size
* expected alignment of CLONE_RANGE and EXTENT_SAME ioctl arguments

Backward compatibility: if the values are 0, kernel does not provide
this information, the applications should ignore them.

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 2f6d7b1..c6c8e35 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2574,6 +2574,10 @@
 	}
 	mutex_unlock(&fs_devices->device_list_mutex);
 
+	fi_args->nodesize = root->fs_info->super_copy->nodesize;
+	fi_args->sectorsize = root->fs_info->super_copy->sectorsize;
+	fi_args->clone_alignment = root->fs_info->super_copy->sectorsize;
+
 	if (copy_to_user(arg, fi_args, sizeof(*fi_args)))
 		ret = -EFAULT;