Triple-nested execution of BenchExec fails with "[Errno 22] Creating overlay mount for '...' failed: Invalid argument"

[PhilippWendler]

Nesting for example runexec or containerexec into a run of BenchExec works, but it starts to fail once three layers of BenchExec are involved and overlay mode is used for some directory in all three of the layers.

Examples that work (two layers, or three without overlay):

bin/containerexec --read-only-dir / --overlay-dir /home -- bin/containerexec --read-only-dir / --overlay-dir /home -- bash
bin/containerexec --read-only-dir / -- bin/containerexec --read-only-dir / -- bin/containerexec --read-only-dir / -- bash

Example that fails with BenchExec 3.25:

bin/containerexec --read-only-dir / --overlay-dir /home -- bin/containerexec --read-only-dir / --overlay-dir /home -- bin/containerexec --read-only-dir / --overlay-dir /home -- bash

The error message in this case is

Failed to configure container with operation 'raise OSError(': [Errno 22] Creating overlay mount for '/home' failed: Invalid argument. Please use other directory modes, for example '--read-only-dir /home'.

The reason for this is that nesting overlayfs is only supported up to depth 2 in the kernel.

This issue is just for the record and for making it possible for users to find this error message in our tracker, because we already have a solution. Using fuse-overlayfs, i.e., #928, will not just help against #776, but also solve this issue. #1062 is going to implement this.

Ping @ricffb because this might interest you.