[parted-devel] [PATCH 6/6] libparted: fix optimal IO alignment

[Jim Meyering]

Phillip Susi wrote:
> There were several apparently incorrect tests that would
> cause certain kernel supplied optimal io size to be discarded in
> favor of the default 1MB alignment, such as 1.5 MB.  Remove these
> tests and accept the kernel value if it is non zero.
> ---
>  libparted/arch/linux.c |   10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
>
> diff --git a/libparted/arch/linux.c b/libparted/arch/linux.c
> index fd4ba32..bbb346a 100644
> --- a/libparted/arch/linux.c
> +++ b/libparted/arch/linux.c
> @@ -2986,15 +2986,7 @@ linux_get_optimum_alignment(const PedDevice *dev)
>             previous logic. */
>          unsigned long optimal_io = blkid_topology_get_optimal_io_size(tp);
>          unsigned long minimum_io = blkid_topology_get_minimum_io_size(tp);
> -        if (
> -            (!optimal_io && !minimum_io)
> -	    || (optimal_io && PED_DEFAULT_ALIGNMENT % optimal_io == 0
> -		&& minimum_io && PED_DEFAULT_ALIGNMENT % minimum_io == 0)
> -	    || (!minimum_io && optimal_io
> -		&& PED_DEFAULT_ALIGNMENT % optimal_io == 0)
> -	    || (!optimal_io && minimum_io
> -		&& PED_DEFAULT_ALIGNMENT % minimum_io == 0)
> -           ) {
> +	if (!optimal_io) {
>              /* DASD needs to use minimum alignment */
>              if (dev->type == PED_DEVICE_DASD)
>                  return linux_get_minimum_alignment(dev);

That code seems to be trying to exclude opt/min values that
do not evenly divide PED_DEFAULT_ALIGNMENT.  That makes sense
only when they're no larger than PED_DEFAULT_ALIGNMENT.
How about keeping the sanity-check, but applying it only
when those values are no larger?  I.e.,

        if (
            (!optimal_io && !minimum_io)
	    || (optimal_io <= PED_DEFAULT_ALIGNMENT
                && PED_DEFAULT_ALIGNMENT % optimal_io == 0
		&& minimum_io <= PED_DEFAULT_ALIGNMENT
                && PED_DEFAULT_ALIGNMENT % minimum_io == 0)
	    || (!minimum_io && optimal_io <= PED_DEFAULT_ALIGNMENT
		&& PED_DEFAULT_ALIGNMENT % optimal_io == 0)
	    || (!optimal_io && minimum_io <= PED_DEFAULT_ALIGNMENT
		&& PED_DEFAULT_ALIGNMENT % minimum_io == 0)
           ) {