F_FORBID_DIR
F_FORBID_DIR | F_FORBID_OPEN, &req->lr_fid);
F_FORBID_DIR | F_FORBID_XATTR, &req->lr_fid);
if ((flags & F_FORBID_DIR) && l9p_fid_isdir(file))
F_FORBID_DIR, &req->lr_fid);