2019-09-26 14:25:18

by Max Reitz

[permalink] [raw]

Subject: [PATCH] xfs: Fix tail rounding in xfs_alloc_file_space()

---

To ensure that all blocks touched by the range [offset, offset + count)
are allocated, we need to calculate the block count from the difference
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=$(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 should
be fully allocated.

With this patch applied, the result is something like this:

$ touch test_file
$ block_size=$(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

Signed-off-by: Max Reitz <[email protected]>
---
fs/xfs/xfs_bmap_util.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index 0910cb75b65d..4f443703065e 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -864,6 +864,7 @@ xfs_alloc_file_space(
xfs_filblks_t allocatesize_fsb;
xfs_extlen_t extsz, temp;
xfs_fileoff_t startoffset_fsb;
+ xfs_fileoff_t endoffset_fsb;
int nimaps;
int quota_flag;
int rt;
@@ -891,7 +892,8 @@ xfs_alloc_file_space(
imapp = &imaps[0];
nimaps = 1;
startoffset_fsb = XFS_B_TO_FSBT(mp, offset);
- allocatesize_fsb = XFS_B_TO_FSB(mp, count);
+ endoffset_fsb = XFS_B_TO_FSB(mp, offset + count);
+ allocatesize_fsb = endoffset_fsb - startoffset_fsb;

/*
* Allocate file space until done or until there is an error
--
2.23.0

2019-09-26 14:39:58

by Darrick J. Wong

[permalink] [raw]

Subject: Re: [PATCH] xfs: Fix tail rounding in xfs_alloc_file_space()

---

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 difference
> 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=$(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 should
> be fully allocated.
>
> With this patch applied, the result is something like this:
>
> $ touch test_file
> $ block_size=$(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

Code looks ok; by any chance do you have an xfstest we could add to the
regresion test suite?

--D

> Signed-off-by: Max Reitz <[email protected]>
> ---
> fs/xfs/xfs_bmap_util.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index 0910cb75b65d..4f443703065e 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -864,6 +864,7 @@ xfs_alloc_file_space(
> xfs_filblks_t allocatesize_fsb;
> xfs_extlen_t extsz, temp;
> xfs_fileoff_t startoffset_fsb;
> + xfs_fileoff_t endoffset_fsb;
> int nimaps;
> int quota_flag;
> int rt;
> @@ -891,7 +892,8 @@ xfs_alloc_file_space(
> imapp = &imaps[0];
> nimaps = 1;
> startoffset_fsb = XFS_B_TO_FSBT(mp, offset);
> - allocatesize_fsb = XFS_B_TO_FSB(mp, count);
> + endoffset_fsb = XFS_B_TO_FSB(mp, offset + count);
> + allocatesize_fsb = endoffset_fsb - startoffset_fsb;
>
> /*
> * Allocate file space until done or until there is an error
> --
> 2.23.0
>

2019-09-26 14:43:29

by Max Reitz

[permalink] [raw]

Subject: Re: [PATCH] xfs: Fix tail rounding in xfs_alloc_file_space()

---

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 difference
>> 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=$(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 should
>> be fully allocated.
>>
>> With this patch applied, the result is something like this:
>>
>> $ touch test_file
>> $ block_size=$(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
>
> Code looks ok; by any chance do you have an xfstest we could add to the
> regresion test suite?
I’ll look into it.

Max

---

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2019-09-30 07:50:13

by Christoph Hellwig

[permalink] [raw]

Subject: Re: [PATCH] xfs: Fix tail rounding in xfs_alloc_file_space()

---

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 difference
> 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:

Looks fine:

Reviewed-by: Christoph Hellwig <[email protected]>

2019-09-30 23:07:06

by Darrick J. Wong

[permalink] [raw]

Subject: Re: [PATCH] xfs: Fix tail rounding in xfs_alloc_file_space()

---

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 difference
> 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=$(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 should
> be fully allocated.
>
> With this patch applied, the result is something like this:
>
> $ touch test_file
> $ block_size=$(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
>
> Signed-off-by: Max Reitz <[email protected]>

Looks ok, will test...
Reviewed-by: Darrick J. Wong <[email protected]>

--D

> ---
> fs/xfs/xfs_bmap_util.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index 0910cb75b65d..4f443703065e 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -864,6 +864,7 @@ xfs_alloc_file_space(
> xfs_filblks_t allocatesize_fsb;
> xfs_extlen_t extsz, temp;
> xfs_fileoff_t startoffset_fsb;
> + xfs_fileoff_t endoffset_fsb;
> int nimaps;
> int quota_flag;
> int rt;
> @@ -891,7 +892,8 @@ xfs_alloc_file_space(
> imapp = &imaps[0];
> nimaps = 1;
> startoffset_fsb = XFS_B_TO_FSBT(mp, offset);
> - allocatesize_fsb = XFS_B_TO_FSB(mp, count);
> + endoffset_fsb = XFS_B_TO_FSB(mp, offset + count);
> + allocatesize_fsb = endoffset_fsb - startoffset_fsb;
>
> /*
> * Allocate file space until done or until there is an error
> --
> 2.23.0
>