[LTP] Rewrite ftrace_regression tests with new C API

[linuxtestproject.agent@gmail.com]

Hi lufei,

On Tue, 28 Apr 2026, lufei wrote:
> Rewrite ftrace_regression tests with new C API
>
> Rewritten from old shell scripts.

Please explain why the conversion is being done — "Rewritten from old
shell scripts" only states what, not why. Also, this bundles two
independent test rewrites; please split into one commit per test.

> +static void run(void)
> +{
> +	int i;
> +
> +	for (i = 0; i < LOOP; i++) {
> +		SAFE_FILE_PRINTF(STACK_TRACER_PATH, "1");
> +		SAFE_FILE_PRINTF(TRACE_OPTIONS, "userstacktrace");

trace_options is modified but never saved/restored. The original
ftrace_lib.sh saved old_trace_options and restored it in
restore_old_setting(). Add TRACE_OPTIONS to .save_restore.

> +	SAFE_FILE_PRINTF(page_fault_path, "%d", page_fault_origin);

This restore only runs on the normal path. If run() aborts via
tst_brk() inside the loop the enable flag is left set. Use .save_restore
or a dedicated cleanup() instead.

[...]

> +static void run(void)
> +{
> +	int i;
> +	const char *const cmd_ls[] = {"ls", "-l", "/sys/kernel/tracing/", NULL};

/sys/kernel/tracing/ is not guaranteed to exist on all configs. The
original used /proc; keep that or add an access() check with TCONF.

> +	SAFE_FILE_PRINTF(SET_EVENT, "signal:signal_generate");
> +	SAFE_FILE_PRINTF(TRACING_ON, "1");

Neither SET_EVENT nor TRACING_ON is restored. Add both to .save_restore.

---
Pre-existing issues noticed in the surrounding code (not introduced
by this patch):

- ftrace_lib.sh:109 — typo "function_pofile_enabled" (should be
  "function_profile_enabled") prevents restoring profile state

---
Note:

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