shiftfs incompatible with overlayfs without specific overlayfs version

[hxx-fetch]

There seems to be an additional kernel patch in conjunction with shiftfs when used above overlayfs:

https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/focal/commit/fs/overlayfs?id=d24b8a547be1578cb5a200ad9ac57a258f0a9de1

So it should be noted in the documentation not to use this dkms in conjunction with overlayfs.

[toby63]

For everyone reading this issue I want to give a summary:

Note: The following information might be outdated.

Problem:
The problem is that overlayfs cannot be used inside a container, when the container software uses shiftfs.
Note: This is only a problem for special use cases, e.g. running Docker with the overlayfs-storage-driver inside an LXD container.

Solution:
A solution is available in form of kernel patches for the overlayfs module (see ubuntu kernel commit).
But these patches are not included in the mainline kernel.
To my knowledge only Ubuntu included them in their kernel.

Main (potential) Workaround:

• patch the kernel module "overlayfs" via dkms:
  (or more correct: install a modified/patched version of overlayfs via dkms)
  You can use a similar dkms package (such as this one) and try to edit it for overlayfs.
  Note: This approach is untested, so it might not work (e.g. some modules cannot be "managed" with dkms).

Other Workarounds:

• use Ubuntu:
  Regarding Derivates: it is unknown to me whether Ubuntu derivates (such as mint) include the ubuntu kernel

• convince your distro's kernel maintainers to include the patches

• (not recommended) patch the kernel sources and rebuild the kernel manually (this might take a long time to compile)

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Original Post:
@hxx-fetch:
You are right.
Although this problem is mentioned in a post I linked to in the Readme (see "Further information on shiftfs"), I agree that I should clarify it here in the Readme too.
Quote from the LXD Forum:

Limitations

The only limitation we’re currently aware of is that shiftfs will prevent the use of overlayfs inside the container. This may break Docker users. If this applies to you, you should stay away from shiftfs for now.

I added a note in the Readme (see commit).