linux-kernel - Re: [PATCH 13/13] DRBD: Fix comparison always false warning due to long/long long compare

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Date:	Wed, 12 Oct 2011 15:35:28 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Philipp Reisner <philipp.reisner@...bit.com>,
	David Howells <dhowells@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	drbd-dev@...ts.linbit.com
Subject: Re: [PATCH 13/13] DRBD: Fix comparison always false warning due to
 long/long long compare

On Wed, Oct 12, 2011 at 14:27, Philipp Reisner
<philipp.reisner@...bit.com> wrote:
> From: David Howells <dhowells@...hat.com>
>
> Fix warnings of the following nature in the drbd header:
>
> In file included from drivers/block/drbd/drbd_bitmap.c:32:
> drivers/block/drbd/drbd_int.h: In function 'drbd_get_syncer_progress':
> drivers/block/drbd/drbd_int.h:2234: warning: comparison is always false due to limited range of data
>
> where mdev->rs_total (an unsigned long) is being compared to 1ULL << 32, which
> is always false on a 32-bit machine.

But on 32-bit, unsigned long is never larger than UINT_MAX neither, so
it doesn't
really change anything??

> Signed-off-by: David Howells <dhowells@...hat.com>
> Signed-off-by: Lars Ellenberg <lars.ellenberg@...bit.com>
>
> Signed-off-by: Philipp Reisner <philipp.reisner@...bit.com>
> Signed-off-by: Lars Ellenberg <lars.ellenberg@...bit.com>
> ---
>  drivers/block/drbd/drbd_int.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
> index ece2e4a..de42c7c 100644
> --- a/drivers/block/drbd/drbd_int.h
> +++ b/drivers/block/drbd/drbd_int.h
> @@ -2071,7 +2071,7 @@ static inline void drbd_get_syncer_progress(struct drbd_conf *mdev,
>                 * Note: currently we don't support such large bitmaps on 32bit
>                 * arch anyways, but no harm done to be prepared for it here.
>                 */
> -               unsigned int shift = mdev->rs_total >= (1ULL << 32) ? 16 : 10;
> +               unsigned int shift = mdev->rs_total > UINT_MAX ? 16 : 10;
>                unsigned long left = *bits_left >> shift;
>                unsigned long total = 1UL + (mdev->rs_total >> shift);
>                unsigned long tmp = 1000UL - left * 1000UL/total;

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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