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SubjectRe: [PATCH] md: avoid warning for 32-bit sector_t
On Tue, Nov 24 2015, Arnd Bergmann wrote:

> When CONFIG_LBDAF is not set, sector_t is only 32-bits wide, which
> means we cannot have devices with more than 2TB, and the code that
> is trying to handle compatibility support for large devices in
> md version 0.90 is meaningless but also causes a compile-time warning:
>
> drivers/md/md.c: In function 'super_90_load':
> drivers/md/md.c:1029:19: warning: large integer implicitly truncated to unsigned type [-Woverflow]
> drivers/md/md.c: In function 'super_90_rdev_size_change':
> drivers/md/md.c:1323:17: warning: large integer implicitly truncated to unsigned type [-Woverflow]
>
> This adds a check for CONFIG_LBDAF to avoid even getting into this
> code path, and also adds an explicit cast to let the compiler know
> it doesn't have to warn about the truncation.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> Noticed on ARM randconfig builds with recent gcc versions.
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 0b48c5d7c489..ee9a7ab44f32 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -1025,8 +1025,9 @@ static int super_90_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor
> * (not needed for Linear and RAID0 as metadata doesn't
> * record this size)
> */
> - if (rdev->sectors >= (2ULL << 32) && sb->level >= 1)
> - rdev->sectors = (2ULL << 32) - 2;
> + if (IS_ENABLED(CONFIG_LBDAF) && (u64)rdev->sectors >= (2ULL << 32) &&
> + sb->level >= 1)
> + rdev->sectors = (sector_t)(2ULL << 32) - 2;
>
> if (rdev->sectors < ((sector_t)sb->size) * 2 && sb->level >= 1)
> /* "this cannot possibly happen" ... */
> @@ -1319,8 +1320,9 @@ super_90_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
> /* Limit to 4TB as metadata cannot record more than that.
> * 4TB == 2^32 KB, or 2*2^32 sectors.
> */
> - if (num_sectors >= (2ULL << 32) && rdev->mddev->level >= 1)
> - num_sectors = (2ULL << 32) - 2;
> + if (IS_ENABLED(CONFIG_LBDAF) && (u64)num_sectors >= (2ULL << 32) &&
> + rdev->mddev->level >= 1)
> + num_sectors = (sector_t)(2ULL << 32) - 2;
> md_super_write(rdev->mddev, rdev, rdev->sb_start, rdev->sb_size,
> rdev->sb_page);
> md_super_wait(rdev->mddev);

applied, thanks.
NeilBrown
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