bug#30875: Garbage collector may leave empty files

[Mark H Weaver <mhw@netris.org>]

ludo@gnu.org (Ludovic Courtès) writes:

> Marius Bakke <mbakke@fastmail.com> skribis:
>
>> Recently I've seen a couple of instances like these:
>>
>> exporting path `/gnu/store/mi1rbw8fdsbi4bc4pndbb6smq39722vm-baobab-3.26.1.tar.xz'
>> guix offload: error: build failed: hash of path
>> `/gnu/store/mi1rbw8fdsbi4bc4pndbb6smq39722vm-baobab-3.26.1.tar.xz'
>> has changed from
>> `4223b4813b2253e68ea2b824d0d0e284ff75714ad0faf5a33d65a78df6b65915'
>> to
>> `77ac62e2629d8e45f624589c0c8bf99e24b3a722349bf1e79bc186008534e246'!
>> cannot build derivation `/gnu/store/jbx6a4n1d55dpydr87d11m7xwapm3pcx-gnome-3.24.3.drv': 1 dependencies couldn't be built
>>
>> Without the build hook, it manifests as:
>>
>> starting phase `unpack'
>> tar: This does not look like a tar archive
>> xz: (stdin): File format not recognized
>> tar: Child returned status 1
>> tar: Error is not recoverable: exiting now
>>
>> There was another instance on help-guix recently with a user having
>> empty .drv files in the store.
>>
>> There is a bug lurking here somewhere, but I'm not sure where to start
>> looking.
>>
>> $ find /gnu/store/ -maxdepth 1 -size 0 | grep -v '\.lock$' | wc -l
>> 24
>
> Are we sure this is a Guix issue and not a disk or file system
> corruption issue?  The relevant code in guix-daemon hasn’t changed in
> ages.
>
> What file system are you using?  Btrfs?  :-)

The ext[234] filesystems are well known for leaving zero-length files
around after a crash.  So far, I've never seen Btrfs do that, and I
wouldn't expect it to based on its design.  That's partly why I switched
to it.

      Mark