GNU bug report logs - #56391
`cp --reflink=always` creates empty file on failure

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Message #23 received at 56391 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Pádraig Brady <P <at> draigBrady.com>
Cc: bgilbert <at> backtick.net, 56391 <at> debbugs.gnu.org
Subject: Re: bug#56391: `cp --reflink=always` creates empty file on failure
Date: Wed, 6 Jul 2022 14:48:33 -0500

[Message part 1 (text/plain, inline)]

On 7/6/22 06:17, Pádraig Brady wrote:
> This will usually work, but there are cases where this may lose data,
> as previously discussed at:
>
> https://bugzilla.redhat.com/show_bug.cgi?id=921708
> http://lists.gnu.org/archive/html/coreutils/2013-03/msg00056.html
>
> I'm not sure cp can robustly clean up in this situation? 

Thanks for pointing me to those old discussions. As I understand it, the 
worry is that FICLONE will only partly succeed, causing the destination 
file to contain some (but not all) the input data, and then if we remove 
the output file we'll lose the newly-made partial clone. I don't know 
whether FICLONE can do that, but it sounds like a reasonable worry.

If that understanding is correct, then the attached further patch should 
suffice, so I boldly installed it.

[0001-cp-don-t-remove-nonempty-cloned-dest.patch (text/x-patch, attachment)]

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