feat: Enhance VFolder mount with additional explicit and verbose options

[rapsealk]

This PR resolves #1836 by introducing a new handler, prepare_mount_arg_v2().

For instance, users can now use the following formats with two VFolders: test-folder-808 with READ_WRITE permission and test-folder-809 with READ_ONLY permission.

1. Users can use the same format as NAME[=PATH] or NAME[:PATH], as shown below:

$ ./backend.ai run --rm --mount test-folder-808:/home/work/abc ...

2. Additionally, the format below is supported:

$ ./backend.ai run --rm --mount type=bind,source=test-folder-808,target=/home/work/abc ...

# with explicit READ_ONLY permission
$ ./backend.ai run --rm --mount type=bind,source=test-folder-809,target=/home/work/abc,permission=ro ...
$ ./backend.ai run --rm --mount type=bind,source=test-folder-808,target=/home/work/abc,perm=ro ...

# with explicit READ_WRITE permission
$ ./backend.ai run --rm --mount type=bind,source=test-folder-808,target=/home/work/abc,perm=rw ...

Each field separated by commas is optional, except for the source field, which is mandatory. If permission is ungiven, it will follow the permitted VFolderPermission.

For client, a new parameter mount_options has been added:

mount_options: Mapping[str, Mapping[str, Any]] = {
  "vf-001": {
    "type": "bind",
    "permission": "ro",
  },
}

Checklist: (if applicable)

• Milestone metadata specifying the target backport version
• Mention to the original issue
• Installer updates including:
  • Fixtures for db schema changes
  • New mandatory config options
• Update of end-to-end CLI integration tests in ai.backend.test
• API server-client counterparts (e.g., manager API -> client SDK)
• Test case(s) to:
  • Demonstrate the difference of before/after
  • Demonstrate the flow of abstract/conceptual models with a concrete implementation
• Documentation
  • Contents in the docs directory
  • docstrings in public interfaces and type annotations

[achimnol]

Generally LGTM!
Just let's trafaret-fy MountTypes and MountPermission in the API IV checks.

[rapsealk]

rror(\'{0: DataError(\\\'value should be None\\\'), 1: DataError(\\\'{\\\\\\\'pipeline-0-YynSBt\\\\\\\': DataError(\\\\\\\'{\\\\\\\\\\\\\\\'value\\\\\\\\\\\\\\\': DataError(\\\\\\\\\\\\\\\'{\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'permission\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\': DataError("{0: DataError(\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'value should be None\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'), 1: DataError(\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'value is not a valid member of MountPermission\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\')}")}\\\\\\\\\\\\\\\')}\\\\\\\')}\\\')}\')}')

[achimnol]

The new vfolder mount argument format should be also recognized by the backend.ai session create command as well!

[kyujin-cho]

When would be the case of this old prepare_mount_arg() being utilized on the new code base? I am in doubt of leaving old function on a new code.

[rapsealk]

I was considering keeping the old one for potential use cases. However, it would be reasonable to remove it since the new one (prepare_mount_arg_v2()) supersedes its functionality.

[kyujin-cho]

Yes removing old one looks ideal. Please update the PR accordingly.