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About reflink len = 0 behavior

To: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx>
Subject: About reflink len = 0 behavior
From: Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
Date: Thu, 20 Oct 2016 15:46:50 +0800
Cc: <fstests@xxxxxxxxxxxxxxx>, btrfs <linux-btrfs@xxxxxxxxxxxxxxx>, <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0
Hi Darrick, xfs guys and btrfs guys.

Although such question is quite late as reflink generic tests are in fstests for a long time, I'm still not sure what's the correct behavior for reflink len = 0.

Test case generic/182 is causing different output between btrfs and xfs.

For btrfs, dedupe will just return 0 and check nothing, while for xfs len == 0 means to check the whole file length.

Both makes sense for me, for btrfs len = 0 behavior, it just follows read/write functions. And I assume xfs follows reflink behavior, when len is not specified, then reflink the length of src file.

But since it's a generic test, we need to unify the behavior.

So, which one is the standard and which document should we follow for such behavior definition?

Thanks,
Qu


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