[LTP] readahead02: Fall back to the parent disk's BDI for partitions

[linuxtestproject.agent@gmail.com]

Hi Victor,

On Fri, 21 Aug 2026, Victor Cheng-Yen Yang wrote:
> readahead02: Fall back to the parent disk's BDI for partitions

> +		snprintf(sys_bdi_ra_path, sizeof(sys_bdi_ra_path),
> +			"/sys/class/block/%s/../bdi/read_ahead_kb", backing_dev);
> +		if (access(sys_bdi_ra_path, F_OK))
> +			return;
> +	}
>
> 	SAFE_FILE_SCANF(sys_bdi_ra_path, "%d", &orig_bdi_limit);
>
> 	if (orig_bdi_limit)
> 		SAFE_FILE_PRINTF(sys_bdi_ra_path, "%d", orig_bdi_limit);

Could restoration track whether the value was read separately from its
numeric value? The kernel accepts zero for read_ahead_kb, so if the parent
BDI starts at zero, setup writes a positive value but cleanup skips the
restore. This leaves the parent and its sibling partitions modified after
the test.

Verdict - Needs revision

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