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

[robbieko <robbieko@synology.com>]

Qu Wenruo 於 2018-03-07 17:27 寫到:
> 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?
> 

Currently, only the first extent is checked for shared in extent_map.
Details can refer to "[PATCH 2/2] Btrfs: fix fiemap extent SHARED flag 
error with range clone."


>> 
>> 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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