feat(client): cache-mode get_status + single-flight mount refresh + a…

[bigbigxu]

…sync_cache fire-and-forget

• unified_filesystem: get_status branches by no-mount / FS mode / cache mode; in cache mode calls cv.get_status then check_cache_validity, falls back to UFS when invalid or on error; CacheValidity gains Invalid(Option) to carry UFS status
• unified_filesystem: add invalidate_cache, clear CV cache before open-for-write on mount path; async_cache becomes fire-and-forget (spawn load job in background, return immediately)
• mount_cache: single-flight refresh via refresh_lock to avoid blocking all get_mount while holding write lock during RPC
• master_handler: forbid delete of mount point root (error when path == mount.cv_path)
• curvine_fuse: call invalidate_cache only when handle.writer.is_some() (invalidate cache only after flush/release when file was opened for write)

[Copilot]

Pull request overview

This PR enhances the cache-mode behavior in the unified filesystem by improving get_status for cached files, introducing single-flight mount refresh to avoid redundant concurrent RPC calls, and making the async_cache method fire-and-forget to avoid blocking the caller.

Changes:

• get_status now branches by no-mount / FS mode / cache mode: in cache mode it first checks CV status and validates against UFS, falling back to UFS when cache is invalid; CacheValidity::Invalid now carries an Option<FileStatus> to reuse the UFS status fetched during validation, avoiding duplicate UFS calls.
• async_cache is now a synchronous fire-and-forget method that spawns the job submission in a background task, and open_with_opts invalidates the CV cache before writing to UFS in cache mode. Additionally, FUSE flush/release only invalidate meta cache when the file was opened for writing.
• MountCache::check_update uses a tokio::sync::Mutex for double-checked locking to ensure only one task performs the full mount refresh when the TTL expires. The server now forbids deletion of mount point root directories.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
curvine-client/src/unified/unified_filesystem.rs	Cache-mode get_status with validity check/fallback; fire-and-forget async_cache; cache invalidation on write open; CacheValidity::Invalid now carries optional FileStatus
curvine-client/src/unified/mount_cache.rs	Single-flight mount refresh via tokio::sync::Mutex with double-checked locking pattern
curvine-server/src/master/master_handler.rs	Forbid deletion of mount point root directory
curvine-fuse/src/fs/curvine_file_system.rs	Conditional meta cache invalidation on flush/release only when writer exists
curvine-tests/tests/write_cache_test.rs	Updated test to match new synchronous async_cache signature

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.