GNU bug report logs - #78623
cp --preserve=xattr copies attr as well as xattr which breaks cross-FS copy

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From: Pádraig Brady <P <at> draigBrady.com>
To: Gael Donval <gael.donval <at> manchester.ac.uk>, 78623 <at> debbugs.gnu.org
Subject: bug#78623: cp --preserve=xattr copies attr as well as xattr which breaks cross-FS copy
Date: Thu, 29 May 2025 10:10:48 +0100

On 28/05/2025 16:14, Gael Donval wrote:
> Dear list,
> 
> We've unearth an odd behaviour in cp: `cp --preserve=xattr` tries to copy both attributes of the chattr kind and extended attributes of the getfattr kind with apparently no way to disable either one of them (it's all or nothing). This is problematic in tools like mkosi where non-filesystem-specific xattributes need to be preserved whilst FS-specific attributes must be discarded for cross-filesystem support.
> 
> I have added a MWE at the end of this email after my signature: it creates two raw partitions as files (one as XFS, one as BTRFS), mounts them in local folders and creates 3 files in the BTRFS partitions later altered before copy.
> 
> Referring to the script, we think there should be an option to copy files foo (no-attr), bar (setfattr) and baz (chattr), keeping the setfattr's xattr and discarding chattr's attr. Looking at the code, it seems like cp eventually defers the actual attribute copying libattr, which seems to handle both, but separately (which is what we want).
> 
> Would it make sense to add a separate `attr` preserve value for the chattr case and keep `xattr` for getfattr case?

I've not looked in detail at your case,
but it's worth noting that /etc/xattr.conf
gives the facility to skip copying certain xattrs.
Does that suffice to handle your issue?

thanks,
Pádraig

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