GNU bug report logs - #79267
cp --sparse=auto heuristic fails on a squashfs mounted drive.

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From: Pádraig Brady <P <at> draigBrady.com>
To: Paul Eggert <eggert <at> cs.ucla.edu>, Jeremy Allison <jallison <at> ciq.com>
Cc: 79267 <at> debbugs.gnu.org, hvanderwal <at> ciq.com
Subject: bug#79267: cp --sparse=auto heuristic fails on a squashfs mounted drive.
Date: Sat, 23 Aug 2025 19:01:09 +0100

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

On 23/08/2025 01:48, Paul Eggert wrote:
> On 8/22/25 07:04, Pádraig Brady wrote:
>>         /* Copy this extent, looking for further opportunities to not
>>            bother to write zeros if --sparse=always, since SEEK_HOLE
>>            is conservative and may miss some holes.  */
>>
>> So the comment needs to be tweaked, but a more general issue
>> is that it disables copy offloading (copy_file_range) for sparse files.
> 
> Ouch, I didn't see that. That's a real loss. I installed the first
> attached patch to revert that part of my recent change.

Cool. I'll push the attached test to enforce this
> I assume the part of the change that always punches holes is OK. I
> couldn't see why one would not want to punch a hole if one has already
> taken the trouble to find and create the hole.

Fair enough. It simplifies the code anyway.

>> BTW commit 26bf557 also changed this a couple of weeks ago
>> without updating the comment, so the comment relates to sparse_mode !=
>> SPARSE_ALWAYS.
> 
> Not quite following but I hope the comment is OK now with the first
> patch installed.

Right, I missed that commit 26bf557 didn't actually change the logic
for this line, only the syntax.

thanks!
Padraig

[cp-copy-offload-nfs-test.patch (text/x-patch, attachment)]

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