[draft] Add fallible unmounting

[khanhtranngoccva]

This serves as a more manageable version of #419. I cherry-picked the test cases and the CI modifier that allows these tests to execute. The tests cannot compile as of now, since the PR changed the API interface of umount_and_join.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Add the fixtures module used by this integration test

The new test file declares mod fixtures;, which requires either tests/fixtures.rs or tests/fixtures/mod.rs, but this commit does not add either file. That causes the unmount integration test target to fail compilation with an unresolved module error before any test logic can run.

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[chatgpt-codex-connector]

Update unmount calls to match current umount_and_join API

These tests still use the old umount_and_join contract (umount_and_join(&[]) and tuple-destructuring from expect_err), but in this commit BackgroundSession::umount_and_join takes no arguments and returns io::Result<()> (src/session.rs). This mismatch prevents the test file from compiling, so CI cannot execute the new unmount coverage.

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[khanhtranngoccva]

@cberner I would like to ask if reintroducing the unmount behavior with user-specified flags so that the caller could recover the mount/session object and default to Detach flag otherwise is a good idea.

[cberner]

No, I don't want to add any new unmount behavior, until there's a test that clearly shows what is wrong with the current behavior

[khanhtranngoccva]

I modified the test cases to match the unmounting behavior specified, and modified CI to include testing as root. There are a few inconsistencies I've found so far:

1. If AutoUnmount is enabled, dropping the unmount socket in fuse_pure does not cause the lazy unmount to work as intended. It causes the join thread to hang, and removing that would solve the issue.
2. In fuse_pure, libc_umount runs first, and fuse_unmount_pure only runs as a fallback if the user is not root. These two implementations are not consistent - on Linux, libc_umount (as root) runs unmount calls without any flags, while fuse_unmount_pure (as non-root, since direct unmount calls do not work) always runs with detach/lazy.

[khanhtranngoccva]

@cberner Please let me know what behavior you want because currently, the unmounting behavior is non-deterministic and not well-defined in Linux.

As far as I know, the current libfuse3 implementations is also leaky and not well defined as mentioned by the previous PR(s), as it does not call fuse_session_destroy if on root.

[cberner]

CI is failing, so I haven't looked at the test yet. Can you fix that? You can mark the new test #[ignore] or it's fine if that single test fails. But there are compilation issues right now

[khanhtranngoccva]

CI is failing, so I haven't looked at the test yet. Can you fix that? You can mark the new test #[ignore] or it's fine if that single test fails. But there are compilation issues right now

The test is ready. I think that you should copy the CI commands and manually test them as root and as a normal user because these two cannot be tested at the same time in a single GitHub action (yet). In the future, the toggle whether to run as root or not can be put in a strategy matrix, but I don't have experience doing GitHub CI yet.

cargo test --all --features=libfuse,${{ matrix.features }}
cargo test --all --features=${{ matrix.features }}
cargo test --config "target.'cfg(test)'.runner = 'sudo -E'" --all --features=libfuse,${{ matrix.features }}
cargo test --config "target.'cfg(test)'.runner = 'sudo -E'" --all --features=${{ matrix.features }}