Improve error handling when mounts fail

[mdegat01]

Proposed change

When we fail to mount a media or share type mount it is supposed to mount a read-only file in that spot. This ensures that attempts to write to that folder will fail and report rather then essentially silently fail by writing locally (and then creating other issues later). This logic did not work because it relied on user permissions and all docker containers in the Home Assistant ecosystem run as root. This changes the bind mount itself to use the read-only option which causes write failures even for root.

Since there was a feature request to create mounts of type media and share as read-only this was extended into a feature. Users can now make read-only mounts of type media and share.

As for backup type mounts, we expected that if the user tried to make a backup on a downed mount they would get a timeout. It appears that instead it writes the file locally instead. This causes impossible to fix errors next startup as we cannot mount over a non-empty folder and users can't see these folders without going into the supervisor container.

So if the user tries to make a backup in a mount we first check that the folder is in fact a mountpoint using Path.is_mount. In testing this only returns true if the folder is a mountpoint and if that connection is active. If this returns false we raise an error immediately and exit.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (which adds functionality to the supervisor)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes For discussion/architecture: Network Storage Issues: Proposed fix for: home-assistant/core #106446 #4856
• This PR is related to issue:
• Link to documentation pull request: Document read_only option for mounts developers.home-assistant#2071
• Link to cli pull request: Add support for making read-only mounts cli#451

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Black (black --fast supervisor tests)
• Tests have been added to verify that the new code works.

If API endpoints of add-on configuration are added/changed:

• Documentation added/updated for developers.home-assistant.io

[jmealo]

@mdegat01 thanks for taking care of this! 🙏