Re: [atomic-devel] Fedora 26 change: using overlayfs as default

[Jonathan Lebon <jlebon redhat com>]

The Docker docs also has a breakdown of incompatibilities:

https://docs.docker.com/engine/userguide/storagedriver/overlayfs-driver/#/overlayfs-compatibility

Notably, there's the open(2) issue that has already been
mentioned. The second issue is that rename(2) can fail if
trying to move a dir across the lower and upper dirs:

$ mkdir lower upper work merged
$ mkdir lower/dir
$ sudo mount -t overlay overlay \
    -olowerdir=$PWD/lower,upperdir=$PWD/upper,workdir=$PWD/work \
    merged
$ python -c 'import os; os.rename("merged/dir", "merged/dir2")'
Traceback (most recent call last):
    File "<string>", line 1, in <module>
    OSError: [Errno 18] Invalid cross-device link

So you have to watch for EXDEV and fall back on copying.