rem: err = EBADF;
add: err = FS_EBADF;
context: sys_ioctl(bool kernel, int fd, int cmd, void *arg, size_t sz){    ofile       *f;    int         err;    vnode       *vn;    op_ioctl    *op;    f = get_fd(kernel, fd, FD_FILE);    if (!f) {        err = EBADF;        goto error1;    }    vn = f->vn;    op = vn->ns->fs->ops.ioctl;    if (op)        err = (*op)(vn->ns->data, vn->data, f->cookie, cmd, arg, sz);    else        err = EINVAL;    if (err)        goto error2;    put_fd(f);    return 0;error2:    put_fd(f);error1:    return err;}