netdev - Re: [PATCH 2/8] bitmap: Introduce bitmap_set, bitmap_clear, bitmap_find_next_zero

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Date:	Sat, 17 Oct 2009 23:43:56 +0900
From:	Akinobu Mita <akinobu.mita@...il.com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	davem@...emloft.net, sparclinux@...r.kernel.org,
	benh@...nel.crashing.org, paulus@...ba.org,
	linuxppc-dev@...abs.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, gregkh@...e.de,
	LW@...o-electronics.de, linux-usb@...r.kernel.org,
	rolandd@...co.com, yevgenyp@...lanox.co.il, netdev@...r.kernel.org,
	tony.luck@...el.com, fenghua.yu@...el.com,
	linux-ia64@...r.kernel.org, linux-altix@....com
Subject: Re: [PATCH 2/8] bitmap: Introduce bitmap_set, bitmap_clear, 
	bitmap_find_next_zero_area

2009/10/17 FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>:
> On Tue, 13 Oct 2009 18:10:17 +0900
> Akinobu Mita <akinobu.mita@...il.com> wrote:
>
>> My user space testing exposed off-by-one error find_next_zero_area
>> in iommu-helper. Some zero area cannot be found by this bug.
>>
>> Subject: [PATCH] Fix off-by-one error in find_next_zero_area
>>
>> Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
>> ---
>>  lib/iommu-helper.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/lib/iommu-helper.c b/lib/iommu-helper.c
>> index 75dbda0..afc58bc 100644
>> --- a/lib/iommu-helper.c
>> +++ b/lib/iommu-helper.c
>> @@ -19,7 +19,7 @@ again:
>>       index = (index + align_mask) & ~align_mask;
>>
>>       end = index + nr;
>> -     if (end >= size)
>> +     if (end > size)
>
> I think that this is intentional; the last byte of the limit doesn't
> work.

It looks ok to me. Without above change, find_next_zero_area cannot
find a 64 bits zeroed area in next sample code.

        unsigned long offset;

        DECLARE_BITMAP(map, 64);

        bitmap_clear(map, 0, 64);
        offset = find_next_zero_area(map, 64, 0, 64, 0);
        if (offset >= 64)
                printf("not found\n");
        else
                printf("found\n");
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