Importing LXD image without privileged permissions silently fails reporting success

[ospalax]

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Description
Importing LXD image in constrained environment (e.g.: container) will report success but actually will store only empty disk. The reason for it is that mounting of the file as fs will silently fail due to restricted permissions.

To Reproduce
Run OpenNebula frontend in the container and try to import LXD image (you can try to use my project https://github.com/ospalax/onedocker) - the import will seem ok - but when you look inside the actual file - you will see only empty ext4 fs.

Expected behavior
Just fail.

Details

• Affected Component: Storage
• Hypervisor: LXD
• Version: 5.12

Progress Status

• Branch created
• Code committed to development branch
• Testing - QA
• Documentation
• Release notes - resolved issues, compatibility, known issues
• Code committed to upstream release/hotfix branches
• Documentation committed to upstream release/hotfix branches

[rsmontero]

Added it also to resolved issues