Re: [PATCH 0/2] btrfs fiemap related BUG fix.

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2018年03月07日 16:20, robbieko wrote:
> From: Robbie Ko <robbieko@synology.com>
> 
> This patchset intends to fix btrfs fiemap related bug.
> 
> The fiemap has the following problems:
> 
> 1) Wrong extent count when fm_extent_count is zero.
> 
> 
> 2) SHARED bit is not correct
> I have two ideas, but I do not know which one is the best.
> 
> Like:
>  # dd if=/dev/zero bs=16K count=2 oflag=dsync of=/mnt/btrfs/file
>  # xfs_io -c "fiemap -v" /mnt/btrfs/file
>      /mnt/btrfs/file:
>      EXT: FILE-OFFSET      BLOCK-RANGE      TOTAL FLAGS
>        0: [0..63]:         4241424..4241487    64   0x1
>  # cloner -s $((16*1024)) /mnt/btrfs/file /mnt/btrfs/file_clone
> 
> 1. When any extent is shared in extent map, the entire extent map is shared
>  # xfs_io -c "fiemap -v" /mnt/btrfs/file
>      /mnt/btrfs/file:
>      EXT: FILE-OFFSET      BLOCK-RANGE      TOTAL FLAGS
>        0: [0..63]:         4241424..4241487   64  0x2001

I think this is what btrfs is doing right now.
Although I'm not sure if this is the best solution.

BTW, I just did the same operation, and just get the SHARED flag on both
source and destination.

Is there something wrong?

> 
> 2. Split into different extent
>  # xfs_io -c "fiemap -v" /mnt/btrfs/file
>      /mnt/btrfs/file:
>      EXT: FILE-OFFSET      BLOCK-RANGE      TOTAL FLAGS
>        0: [0..31]:         4241424..4241455   32  0x0
>        1: [32..63]:        4241456..4241487   32  0x2001

This is what XFS does.

Thanks,
Qu

> 
> Robbie Ko (2):
>   Btrfs: fiemap: pass correct bytenr when fm_extent_count is zero
>   Btrfs: fix fiemap extent SHARED flag error with range clone.
> 
>  fs/btrfs/extent_io.c | 150 ++++++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 132 insertions(+), 18 deletions(-)
> 
> --
> 1.9.1
> 
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