Upstream kernels since v5.12-rc6-1-g4c5b479975 have added the ->fileattr_get() and ->fileattr_set() methods in struct inode_operations to get/set the FS_*_FL flags on inodes instead of going through the ->ioctl() method.

If the ->fileattr_get() and ->fileattr_set() methods are not defined, the do_vfs_ioctl() call will fall back to calling ->vfs_ioctl()->unlocked_ioctl(), but it is useful for some stacking filesystems (e.g. overlayfs).