Re: [PATCH v2] xfs: fix exchange-range reflink flag clearing issue with INO1_WRITTEN

[m00nb1rd lin <ljp1205831794@gmail.com>]

在 2026/7/28 11:14, Christoph Hellwig 写道:
> On Tue, Jul 28, 2026 at 10:23:03AM +0800, Lin Jiapeng wrote:
>> When exchanging two full-file ranges, xmi_can_exchange_reflink_flags()
>> can move the reflink inode flag from the file that currently has it to
>> the other file, as long as exactly one side is marked.  This assumes
>> that the file contents, and therefore all shared extents, are exchanged.
>>
>> That assumption is not true when XFS_EXCHMAPS_INO1_WRITTEN is set.
>> xfs_exchmaps_can_skip_mapping() can skip hole and unwritten mappings
>> from file1, so an exchange can complete without moving every mapping
>> that the earlier flag-swap decision accounted for.  In that case the
>> post-operation cleanup can clear the reflink flag from an inode that
>> still owns shared written extents.  Later writes then take the
>> non-reflink write path and may update blocks that should still have
>> been protected by CoW, which shows up as data corruption between
>> reflink-related files.
>>
>> Fix this by disabling the reflink flag exchange whenever
>> XFS_EXCHMAPS_INO1_WRITTEN is requested.  The contents exchange can still
>> proceed; the conservative outcome is that both inodes keep the reflink
>> flag.  The regular reflink flag cleanup path can drop the extra flag
>> later once the inode no longer has shared extents.
> 
> The fix looks good:
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> 
> Can you add a test case to fstests for this?
> 

Thanks for the review. Sure, I'll add an fstests regression test and 
send it separately.