[sidick]

Summary

Issue #160's "Tier 3" follow-up to #159/#161/#162's dos.library gap scan.

• MakeLink/ReadLink: real AmigaOS soft-link semantics map naturally onto a host symlink, hard-link onto a host hard link.

  • MakeLink(name, dest, soft) (doslock.rs): soft == FALSE creates a real std::fs::hard_link from dest's lock; soft != FALSE creates a real symlink (#[cfg(unix)] via std::os::unix::fs::symlink) pointing at dest's Amiga path, resolved via ResolveMode::ParentMustExist so the target need not exist yet (soft-link targets are "resolved lazily", per the NDK autodoc). name itself also uses ParentMustExist and fails with ERROR_OBJECT_EXISTS if something's already there, matching CreateDir's own convention.
  • ReadLink(port, lock, path, buffer, size) (doslock.rs): resolves lock's directory + relative path, calls std::fs::read_link on a real host symlink, and writes the raw target string back (not a re-derived Amiga path -- see the doc comment on DosState::read_link for why that's the most faithful thing to report).

• LockRecord/LockRecords/UnLockRecord/UnLockRecords (dosfile.rs): cheap stubs matching this runtime's existing no-real-concurrency posture (InitSemaphore/ObtainSemaphore, AddTask, ChangeMode). LockRecord/UnLockRecord validate the filehandle is currently open; LockRecords/UnLockRecords always report success (there's no single real-AmigaOS struct layout for recArray to validate against, and nothing to enforce either way).

Judgment calls

1. Soft-link target resolve mode: MakeLink's dest Amiga path (for a soft link) is resolved via ResolveMode::ParentMustExist -- the closest existing primitive that turns an Amiga path into a host path without requiring the target to already exist, matching real AmigaOS's documented "resolved lazily" soft-link semantics.

2. ST_SOFTLINK detection in Examine/ExNext/ExAll -- deliberately cut. fill_fib (doslock.rs) and dosexall.rs's equivalent scan use std::fs::metadata, which follows symlinks, so a soft link currently lists as whatever it resolves to (or fails to list at all if dangling). Detecting it would need symlink_metadata + is_symlink() at every fill_fib call site -- cut for scope rather than touching that shared, already-tested machinery. Documented explicitly in doslock.rs's module docs.

3. Windows symlink creation: gated #[cfg(unix)]; on any other target, MakeLink(soft) reports a clean ERROR_ACTION_NOT_KNOWN (never a panic/hang) without attempting the host call at all, since Windows symlink creation needs elevated privileges/Developer Mode that can't be known in advance, and there's no dedicated real-AmigaOS error code for "this filesystem doesn't support soft links".

4. ReadLink's port argument: read (so the real register convention holds) but otherwise unused. Real ReadLink is normally called by DOS itself after a filesystem handler process's packet reply comes back ERROR_IS_SOFT_LINK, and port identifies that handler for a real multi-process AmigaOS to route back to. This runtime has no real per-filesystem handler process for ordinary volumes (same posture as dosdevproc.rs/dospkt.rs), and read_link resolves everything directly from self.locks + the host filesystem -- so there's no handler for port to identify, and ignoring it changes nothing observable.

Also not implemented (out of scope per the issue): the real AmigaOS "filesystem returns ERROR_IS_SOFT_LINK, DOS calls ReadLink, retries" protocol inside Lock/Open/Examine. Host symlinks already transparently resolve via ordinary host filesystem calls, so Lock/Open/Examine "just work" on a soft link without any extra code here.

Test plan

• Unit tests for every new DosState method (doslock.rs/dosfile.rs): success paths, every documented failure path (ERROR_OBJECT_EXISTS, ERROR_INVALID_LOCK, ERROR_OBJECT_WRONG_TYPE, mapped I/O errors), plus #[cfg(unix)]/#[cfg(not(unix))]-gated symlink-specific cases.
• Real end-to-end tests driving actual A-line trap dispatch for all 6 calls at their real LVO offsets (MakeLink -444, ReadLink -438, LockRecord -270, LockRecords -276, UnLockRecord -282, UnLockRecords -288).
• cargo test --workspace (1102 tests, up from 1080) passes; cargo clippy --all-targets -- -D warnings and cargo fmt --all --check clean.

Closing

Addresses #160. Fully implements MakeLink/ReadLink/LockRecord/LockRecords/UnLockRecord/UnLockRecords as scoped by the issue. Deliberately deferred (see judgment call #2 above): ST_SOFTLINK reporting in Examine/ExNext/ExAll for a host symlink entry -- not implemented, documented in doslock.rs's module docs as a scope cut, not a bug.

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