linux-kernel - Re: [PATCH] xfs: Fix tail rounding in xfs_alloc_file

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Date:   Thu, 26 Sep 2019 07:37:14 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Max Reitz <mreitz@...hat.com>
Cc:     linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Brian Foster <bfoster@...hat.com>
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 <mreitz@...hat.com>
> ---
>  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
>