* mount: skip directory caching on file lookup and write
When opening or creating a file in a directory that hasn't been cached yet,
don't list the entire directory. Instead:
- For reads: fetch only the single file's metadata directly from the filer
- For writes: create on filer but skip local cache insertion
This fixes a performance issue where opening a file in a directory
with millions of files would hang because EnsureVisited() had to
list all entries before the open could complete.
The directory will still be cached when explicitly listed (ReadDir),
but individual file operations now bypass the full directory caching.
Key optimizations:
- Extract shared lookupEntry() method to eliminate code duplication
- Skip EnsureVisited on Lookup (file open)
- Skip cache insertion on Mknod, Mkdir, Symlink, Link if dir not cached
- Skip cache update on file sync/flush if dir not cached
- If directory IS cached and entry not found, return ENOENT immediately
Fixes#7145
* mount: add error handling for meta cache insert/update operations
Handle errors from metaCache.InsertEntry and metaCache.UpdateEntry calls
instead of silently ignoring them. This prevents silent cache inconsistencies
and ensures errors are properly propagated.
Files updated:
- filehandle_read.go: handle InsertEntry error in downloadRemoteEntry
- weedfs_file_sync.go: handle InsertEntry error in doFlush
- weedfs_link.go: handle UpdateEntry and InsertEntry errors in Link
- weedfs_symlink.go: handle InsertEntry error in Symlink
* mount: use error wrapping (%w) for consistent error handling
Use %w instead of %v in fmt.Errorf to preserve the original error,
allowing it to be inspected up the call stack with errors.Is/As.
