> On 29/05/2025 10:56, Gael Donval wrote: > > On Thu, 2025-05-29 at 10:10 +0100, Pádraig Brady wrote: > > > 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? > > > > As far as I can tell, xattr.conf cannot be used to ignore normal file > > attributes (as opposed to extended attributes), can it? We need a way > > to copy extended attributes without copying normal file attributes. > > Well there is no code in coreutils to copy "chattr" attributes. > It was discussed previously, but we decided not to support those > due to the incompat issues you're hitting.
It does copy them though. If it's not the intent of `preserve=xattr`, I'm afraid it's a bug. My reproducer makes it obvious that it tries to copy them. If you change `mkfs.xfs` to `mkfs.btrfs`, it will all succeed and you'll see chattr attributes are copied. If your remove `-- preserver=xattr`, you'll see chattr attributes are not copied anymore. > > That version of cp are you using? cp (GNU coreutils) 9.7 > > strace may be instructive as to that is reading/writing these chattrs > (this is done with ioctl FS_IOC_GETFLAGS IIRC). I might be wrong but it looks like everything xattr-related is deferred to libattr. I'll investigate that tomorrow! Gaël > > cheers, > Pádraig
