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Subject: Re: [PATCH] xfs: Fix tail rounding in xfs_alloc_file_space()
To:     "Darrick J. Wong" <darrick.wong@oracle.com>
Cc:     linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org,
        Brian Foster <bfoster@redhat.com>
References: <20190926142238.26973-1-mreitz@redhat.com>
 <20190926143704.GA9916@magnolia>
From:   Max Reitz <mreitz@redhat.com>
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Message-ID: <40d1b2d8-5f17-a76d-7124-4b85ac035e80@redhat.com>
Date:   Thu, 26 Sep 2019 16:40:45 +0200
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In-Reply-To: <20190926143704.GA9916@magnolia>
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On 26.09.19 16:37, Darrick J. Wong wrote:
> On Thu, Sep 26, 2019 at 04:22:38PM +0200, Max Reitz wrote:
>> To ensure that all blocks touched by the range [offset, offset + count=
)
>> are allocated, we need to calculate the block count from the differenc=
e
>> of the range end (rounded up) and the range start (rounded down).
>>
>> Before this patch, we just round up the byte count, which may lead to
>> unaligned ranges not being fully allocated:
>>
>> $ touch test_file
>> $ block_size=3D$(stat -fc '%S' test_file)
>> $ fallocate -o $((block_size / 2)) -l $block_size test_file
>> $ xfs_bmap test_file
>> test_file:
>>         0: [0..7]: 1396264..1396271
>>         1: [8..15]: hole
>>
>> There should not be a hole there.  Instead, the first two blocks shoul=
d
>> be fully allocated.
>>
>> With this patch applied, the result is something like this:
>>
>> $ touch test_file
>> $ block_size=3D$(stat -fc '%S' test_file)
>> $ fallocate -o $((block_size / 2)) -l $block_size test_file
>> $ xfs_bmap test_file
>> test_file:
>>         0: [0..15]: 11024..11039
>=20
> Code looks ok; by any chance do you have an xfstest we could add to the=

> regresion test suite?
I=E2=80=99ll look into it.

Max


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