[LTP] safe_stdio: More checks for invalid function return values

[linuxtestproject.agent@gmail.com]

Hi Petr,

--- [PATCH 1/2] ---

On 2026-04-17, Petr Vorel wrote:
> safe_stdio: More checks for invalid function return values

> -	if (ret == EOF)
> -		tst_brkm_(file, lineno, TBROK | TERRNO, NULL, "fflush(%p)", f);
> +	if (ret == EOF) {
> +		tst_brkm_(file, lineno, TBROK | TERRNO, NULL, "fflush(%p) failed", f);
> +	} else if (!ret) {
> +		tst_brkm_(file, lineno, TBROK | TERRNO, NULL,
> +				  "Invalid fflush(%p) return value %d", f, ret);
> +	}

!ret is ret == 0, which is fflush()'s success return — this breaks every
caller on success. fflush() only returns 0 or EOF per POSIX; there is no
invalid return value to guard against, so drop the else if branch entirely.

> +	} else if (ret < 0) {
> +		tst_brkm_(file, lineno, TBROK | TERRNO, NULL,
> +				  "Invalid ftell(%p) return value %ld", f, ret);

> +	} else if (ret < 0) {
> +		tst_brkm_(file, lineno, TBROK | TERRNO, NULL,
> +				  "Invalid fileno(%p) return value %d", f, ret);

Use ret < -1 here to be consistent with safe_fseek() in the same file and
with the policy established by patch 2/2; also fix the continuation-line
indentation (tabs only, no mixed spaces).

--- [PATCH 2/2] ---

On 2026-04-17, Petr Vorel wrote:
> lib: Be pedantic on invalid comparison check

> diff --git a/lib/safe_stdio.c b/lib/safe_stdio.c
> @@ -67,7 +67,7 @@ int safe_asprintf(...)
> -	} else if (ret < 0) {
> +	} else if (ret < -1) {
> ...
> @@ -154,7 +154,7 @@ int safe_fseek(...)
> -	} else if (ret < 0) {
> +	} else if (ret < -1) {

This fixes asprintf and fseek but misses safe_ftell() and safe_fileno()
from patch 1/2, which are left with ret < 0. Either fix them here or
swap the patch order so new checks are written with ret < -1 from the start.

---
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