Deficuet.ROVFS 0.0.1-alpha.15

ROVFS — Read Only Virtual File System

A read-only virtual file system framework for Windows, built on WinFsp via winfsp.net. Targets netstandard2.0, so Unity 2022+ projects can consume it directly.

ReadOnlyFileSystem implements the read half of a WinFsp file system and delegates all data access to a user-supplied data manager. All write operations (Create, Write, Rename, SetDelete) are rejected, and Open denies every write-related NT access bit.

Core types

Contracts expected from implementations

• Flat path lookup. Path resolution is by full path; the intended implementation is two flat dictionaries (files and directories) keyed by the paths WinFsp passes in. These paths are always rooted at \ and use \ separators, regardless of whether the volume is mounted on a drive letter or into an existing empty folder — the mount point prefix never reaches user mode.
• Directory contexts. CreateDirectoryContext runs when a directory is opened and produces an opaque TDirectoryContext; it is handed back for child path joining (GetChildFullPath) during enumeration and passed as-is to CloseContext. A plain string (the directory path) is a sensible choice; GetChildFullPath must not produce doubled backslashes for the root directory, whose path is \.
• Enumeration. GetEntryInfoEnumerable yields EntryInfo<TEntryKey> in a stable, sorted order, since WinFsp resumes directory enumeration by the last returned name (marker). When PassQueryDirectoryPattern is enabled the data manager must also apply the wildcard pattern. A name→index map makes marker lookup O(1); a natural-sort binary search handles markers that are not present verbatim.
• Thread safety. WinFsp calls into the data manager from multiple worker threads concurrently (opens, reads, enumerations, metadata queries). Implementations must be safe for concurrent reads; the intended pattern is populate-once-then-mount, after which the lookup structures are never modified.
• File handles. TryGetFileContext runs per Open; back the handles with FILE_FLAG_OVERLAPPED (see Win32RandomAccess.OpenFileReadOnly) so the same handle can serve concurrent offset-based reads.

WinFsp host settings applied in Init

SectorSize/SectorsPerAllocationUnit = 4096/1, MaxComponentLength = 255, FileInfoTimeout = 60000, CaseSensitiveSearch = false, CasePreservedNames/UnicodeOnDisk/PersistentAcls = true, PassQueryDirectoryPattern = true, FlushAndPurgeOnCleanup = false (no flush or cache purge makes sense on a read-only volume). Volume label, creation time, and total size come from the data manager; free size is always 0.

NuGet Dependencies

• winfsp.net 2.1.25156
  • The installed WinFsp must also be 2.1, otherwise the native dll versions do not match.
• System.Memory 4.6.3
  • Provides the span types on netstandard2.0; consumers (e.g. Unity) must ship this dll as well.