[LTP] [PATCH] syscalls/listmount04: Detect backported commit 78f0e33cd6c9 dynamically

[Cyril Hrubis]

Hi!
>  static void setup(void)
>  {
> -	if (tst_kvercmp(6, 17, 9) >= 0)
> -		kver = AFTER_6_17_9;
> -	else
> -		kver = BEFORE_6_17_9;
> +	/* 1. If kernel is 6.17.9 or newer, it definitively has the new behavior */
> +	if (tst_kvercmp(6, 17, 9) >= 0) {
> +		current_fd_err_behavior = INVALID_FD_RET_EBADF;
> +		return;
> +	}
> +
> +	/* 2. Runtime probe for older kernels:
> +	 * Check if commit 78f0e33cd6c9 was backported by manually issuing
> +	 * a syscall with an invalid mnt_ns_fd (-1).
> +	 */
> +	mnt_id_req probe_req = {
> +		.size = MNT_ID_REQ_SIZE_VER0,
> +		.mnt_id = LSMT_ROOT,
> +		.mnt_ns_fd = -1,
> +		.param = 0
> +	};
> +
> +	tst_syscall(__NR_listmount, &probe_req, mnt_ids, MNT_SIZE, 0);
> +
> +	/* 3. Set global behavior flag based on actual kernel response */
> +	if (errno == EBADF) {
> +		tst_res(TINFO, "Detected backported commit 78f0e33cd6c9 (returns EBADF)");
> +		current_fd_err_behavior = INVALID_FD_RET_EBADF;
> +	} else {
> +		current_fd_err_behavior = INVALID_FD_RET_EINVAL;
> +	}

This is too complicated. I think that we want to settle for:

* new behavior after 6.17.9 (i.e. EBADF)
* any of the two errnos before that (i.e. either EINVAL or EBADF)

For that we should skip to TST_EXP_FAIL_ARR() pass array with only single
errno for all cases but the one one where we need to allow both EINVAL
and EBADF.

-- 
Cyril Hrubis
chrubis@suse.cz