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Date:   Tue, 11 Jan 2022 17:02:39 +0100
From:   David Sterba <dsterba@suse.cz>
To:     Chris Murphy <lists@colorremedies.com>
Cc:     Remi Gauvin <remi@georgianit.com>,
        linux-btrfs <linux-btrfs@vger.kernel.org>
Subject: Re: Case for "datacow-forced" option
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On Sun, Jan 09, 2022 at 09:37:52AM -0700, Chris Murphy wrote:
> On Fri, Jan 7, 2022 at 6:30 PM Remi Gauvin <remi@georgianit.com> wrote:
> I know that zoned disallows nodatacow, but I have no idea what happens
> to files being copied over with file attribute C. Does the entire copy
> fail or just an error when trying to set chattr +C on the file while
> it's still zero length.

If it's plain copy, ther'es no difference, but if it's based on reflink
then the new file will be created without the +C flag and reflink won't
work, leaving a 0 size file.