dkms build leaves empty folders in `/usr/lib/modules/KERNEL/build` behind

[SoongNoonien]

System information

Type	Version/Name
Distribution Name	Arch Linux
Distribution Version	rolling
Kernel Version	6.6.31
Architecture	amd64
OpenZFS Version	2.2.4

Describe the problem you're observing

It seems like the dkms build leaves some empty folder tree in /usr/lib/modules/6.6.31-2-lts/build/module behind. I'm not sure if this is an OpenZFS bug or rather an ArchZFS one. But as far as I know they don't do something special with dkms over on ArchZFS. Maybe it could be a problem with dkms itself? In my case this looks something like that (no folder actually contains any files):

/usr/lib/modules/6.6.31-2-lts/build/module# ls
insgesamt 13K
drwxr-xr-x  3 root root  3 23. Mai 18:23 avl
drwxr-xr-x 12 root root 12 23. Mai 18:23 icp
drwxr-xr-x  3 root root  3 23. Mai 18:23 lua
drwxr-xr-x  3 root root  3 23. Mai 18:23 nvpair
drwxr-xr-x  4 root root  4 23. Mai 18:23 os
drwxr-xr-x  3 root root  3 23. Mai 18:23 unicode
drwxr-xr-x  3 root root  3 23. Mai 18:23 zcommon
drwxr-xr-x  3 root root  3 23. Mai 18:23 zfs
drwxr-xr-x  4 root root  4 23. Mai 18:23 zstd

This has the unwanted side effect that the package manager won't remove old directories under /usr/lib/modules on kernel updates.

Describe how to reproduce the problem

Build the zfs kernel module via dkms.

Include any warning/errors/backtraces from the system logs

Unfortunately there are none.

[SoongNoonien]

Ok, I've looked a little closer and the folders are actually not empty. Probably this is the reason why they aren't removed. There are hidden folders named .deps which contain multiple "dummy" file:

/usr/lib/modules/6.6.31-2-lts/build/module/zfs/.deps$ ls
insgesamt 61K
-rw-r--r-- 1 root root 8 23. Mai 18:23 libicp_la-zfs_impl.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-abd.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-aggsum.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-arc.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-blake3_zfs.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-blkptr.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-bplist.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-bpobj.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-bptree.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-bqueue.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-brt.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-btree.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dbuf.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dbuf_stats.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-ddt.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-ddt_zap.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dmu_diff.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dmu_object.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dmu_objset.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dmu.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dmu_recv.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dmu_redact.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dmu_send.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dmu_traverse.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dmu_tx.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dmu_zfetch.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dnode.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dnode_sync.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dsl_bookmark.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dsl_crypt.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dsl_dataset.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dsl_deadlist.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dsl_deleg.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dsl_destroy.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dsl_dir.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dsl_pool.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dsl_prop.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dsl_scan.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dsl_synctask.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-dsl_userhold.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-edonr_zfs.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-fm.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-gzip.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-hkdf.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-lz4.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-lz4_zfs.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-lzjb.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-metaslab.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-mmp.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-multilist.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-objlist.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-pathname.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-range_tree.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-refcount.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-rrwlock.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-sa.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-sha2_zfs.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-skein_zfs.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-space_map.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-space_reftree.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-spa_checkpoint.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-spa_config.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-spa_errlog.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-spa_history.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-spa_log_spacemap.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-spa_misc.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-spa.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-spa_stats.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-txg.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-uberblock.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-unique.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_draid.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_draid_rand.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_indirect_births.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_indirect_mapping.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_indirect.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_initialize.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_label.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_mirror.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_missing.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_queue.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_raidz_math_aarch64_neon.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_raidz_math_aarch64_neonx2.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_raidz_math_avx2.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_raidz_math_avx512bw.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_raidz_math_avx512f.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_raidz_math.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_raidz_math_powerpc_altivec.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_raidz_math_scalar.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_raidz_math_sse2.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_raidz_math_ssse3.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_raidz.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_rebuild.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_removal.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_root.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-vdev_trim.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zap_leaf.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zap_micro.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zap.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zcp_get.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zcp_global.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zcp_iter.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zcp.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zcp_set.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zcp_synctask.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zfeature.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zfs_byteswap.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zfs_chksum.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zfs_fm.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zfs_fuid.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zfs_ratelimit.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zfs_rlock.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zfs_sa.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zil.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zio_checksum.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zio_compress.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zio_inject.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zio.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zle.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zrlock.Plo
-rw-r--r-- 1 root root 8 23. Mai 18:23 libzpool_la-zthr.Plo

This is the content of such a file:

/usr/lib/modules/6.6.31-2-lts/build/module/zfs/.deps$ cat libzpool_la-zthr.Plo 
# dummy

[AllKind]

Probably this is the reason why they aren't removed. There are hidden folders named .deps which contain multiple "dummy" file:

Yes that is the reason the folder(s) won't get removed.
Looks to me more like a package manager thing, than a dkms thing.
Most likely not a ZFS thing.

[SoongNoonien]

Looks to me more like a package manager thing, than a dkms thing.

I'm not sure how this can be a package manager issue when those files aren't even part of the package database:

$ pacman -Qo /usr/lib/modules/6.6.31-2-lts/build/module/zfs/.deps/libzpool_la-zthr.Plo
error: No package owns /usr/lib/modules/6.6.31-2-lts/build/module/zfs/.deps/libzpool_la-zthr.Plo

That these .../build/module/... folders aren't removed on a kernel update is the intended behavior if they contain files not tracked by the package manager. But that they contain untracked files is what I consider to be a zfs or dkms issue. These files appear when the zfs kernel modules are built via dkms and remain there indefinitely.

[AllKind]

Personally I'm on a Mint (ubuntu based) and still on 2.1.15 maybe there's a difference to a 2.2.x release.
But I use dkms and do not have those .Plo files in /lib/modules or /usr/src.
But I found them below the git source tree.
Googling what they are seems this is correct:

.Plo files are generated outputs of an Automake- and libtool-basedbuild system

How they end up on your system under /usr/lib/modules I don't know - sorry.

[SoongNoonien]

Personally I'm on a Mint (ubuntu based) and still on 2.1.15 maybe there's a difference to a 2.2.x release.

It worked for me until 2.2.3 and started to break after the update to 2.2.4.

Googling what they are seems this is correct:

.Plo files are generated outputs of an Automake- and libtool-basedbuild system

Yes, I found this as well.

How they end up on your system under /usr/lib/modules I don't know - sorry.

They end up under /usr/lib/modules when dkms builds the kernel modules. But they should be cleaned afterwards as they are just some temp data use while compiling. At least as far as I understand this.

[SoongNoonien]

But I found them below the git source tree.

Where did you find them in the git source tree?

[AllKind]

Sorry if I wasn't clear.
In my local git repo, where I build ZFS for my personal computer.

[SoongNoonien]

Ok, yes, this makes sense.

[AllKind]

From what source did you install the zfs-dkms package?
From what I know (and I took a quick look again) OpenZFS only has native support for building rpm and debian packages.
As from the quick look I took, the creation and entries for deletion (in the resulting Makefile(s)) of the .Plo files is entirely handled by autotools.
I'm not saying it is, but I wonder if maybe the maintainer of the Arch package accidentally included the .Plo files in the Arch package for the 2.2.4 release?

[SoongNoonien]

From what source did you install the zfs-dkms package?

archzfs.com

From what I know (and I took a quick look again) OpenZFS only has native support for building rpm and debian packages.

Yes, but building a dkms config is also support, which is what archzfs does.

I'm not saying it is, but I wonder if maybe the maintainer of the Arch package accidentally included the .Plo files in the Arch package for the 2.2.4 release?

No, this is not the case as I've stated above these files are not part of the package database. But here is a list of all files contained in the zfs-dkms package:
files.txt

[SoongNoonien]

Over on dkms I got the answer that this is caused by automake. I'll open a PR with the suggested fix, though I'm not sure if this has any unwanted side effects.