Fix: skip cgroup filesystem type check when cgroups are disabled

[jnovy]

Fixes #1413

Problem

When --cgroup-manager=disabled is used (or --cgroups=disabled via podman), crun still unconditionally calls libcrun_get_cgroup_mode() early in the container startup path. This function does statfs("/sys/fs/cgroup") and returns an error if the filesystem type is neither CGROUP2_SUPER_MAGIC nor TMPFS_MAGIC.

On systems where /sys/fs/cgroup is not a standard cgroup mount — such as Android with Linux Deploy where it is mounted as sysfs — this causes container creation to fail with:

OCI runtime error: crun: invalid file system type on `/sys/fs/cgroup`

This defeats the purpose of --cgroups=disabled, which exists precisely for environments where cgroups are not properly available.

Root Cause

In libcrun_container_run_internal() (container.c), libcrun_get_cgroup_mode() is called before setup_cgroup_manager(), which is where context->force_no_cgroup is evaluated. The same pattern exists in libcrun_set_mounts() (linux.c), where the cgroup mode is queried unconditionally to determine the unified cgroup path.

Fix

Guard the libcrun_get_cgroup_mode() calls and related cgroup logic with checks for context->force_no_cgroup:

• src/libcrun/container.c: Skip the cgroup mode detection and the cgroup v1 deprecation warning when force_no_cgroup is set.
• src/libcrun/linux.c: Skip the cgroup mode detection and unified cgroup path reading in libcrun_set_mounts() when force_no_cgroup is set.

Testing

Added two regression tests in tests/test_cgroup_setup.py:

• test_cgroup_disabled() — verifies that a foreground container with --cgroup-manager=disabled runs successfully without triggering cgroup filesystem validation.
• test_cgroup_disabled_detach() — verifies the same for the create+start (detached) code path.

All existing tests continue to pass.

Reproduction

# On a system where /sys/fs/cgroup is not tmpfs or cgroup2 (e.g., Android/Linux Deploy):
sudo podman run -dt --runtime crun --cgroups=disabled --network=host docker.io/library/httpd
# Before fix: OCI runtime error: crun: invalid file system type on `/sys/fs/cgroup`
# After fix: container starts successfully

Signed-off-by: Jindrich Novy jnovy@redhat.com

[gemini-code-assist]

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[giuseppe]

is this enough to work on a system without /sys/fs/cgroup?

If so, LGTM