Announcing macFUSE 5.1.0

Announcing macFUSE 5.1.0 Posted on 30 Oct 2025

Download macFUSE 5.1.0 macOS 12 or later Apple Silicon or Intel SHA-256: 19e6cc5440d8d68b2352391d30ef3092965f2af4ed9fc0a67f70da2d181d55c2

Update build process to use Xcode 26.1 (macOS 26.1 SDK)
Update demo file systems
- Update LoopbackFS demo file systems and add a libfuse3 variant (LoopbackFS-libfuse3-C)
- Add new HelloFS demo file system (HelloFS-Framework-Swift). It serves as a minimal “Hello World” example — in just 40 lines of code.
- For more information, see the demo repository.

Update kernel extension to version 5.1.0
Add support for the VNOP_MONITOR file system callback

The VNOP_MONITOR callback is available since macOS 15 and notifies file systems when the number of watchers for a file system item changes. This allows distributed file systems to subscribe only to events for items that are actively being watched, improving efficiency and reducing unnecessary event handling.
- When the VNOP_MONITOR callback is invoked, the kernel extension sends a FUSE_MONITOR message (struct fuse_monitor_in) to the file system server running in user space
- The FUSE_MONITOR_BEGIN flag is set when a new watcher starts monitoring the item
- The FUSE_MONITOR_END flag is set when a watcher stops monitoring the item
Fix a bug in VNOP_LINK that can cause a deadlock in case a file system uses the same nodeid to represent both the original file system item and its link. In this case, trying to lock the link in VNOP_LINK resulted in a deadlock. For more information, see macfuse/macfuse#1120.
Fix a bug in VNOP_MNOMAP that can cause a deadlock. The VNOP_WRITE callback might end up calling the VNOP_MNOMAP callback. Attempting to lock the already locked file system item in the VNOP_MNOMAP callback caused the deadlock.
Fix f_mntfromname (fsname mount option) being truncated at 90 bytes. f_mntfromname supports names of up to 1024 bytes (including the terminating \0 character). For more information, see macfuse/macfuse#1123.

Add support for mounting “non-local” volumes (typically distributed file systems) on macOS 26. Mounting “local” volumes (typically physically attached storage) is supported on macOS 15.4 and later macOS versions.
Add support for mount option local. macOS is more aggressive in dealing with “local” volumes. Treat this option as experimental.
Add support for mount option volname=NAME, where NAME is a string. You can use the volname option to specify a name for the volume being mounted.

Add new monitor callback handler and implement support for the new FUSE_MONITOR message. For more information, see “Kernel Extension”.

Add support for mounting file systems using the FSKit backend. By default, the kernel backend is used to mount volumes. When specifying the mount option -o backend=fskit, libfuse3 will use the FSKit backend to mount the file system. For more information, see FUSE Backends.
Add new monitor callback handler and implement support for the new FUSE_MONITOR message. For more information, see “Kernel Extension”.
Add utimens API extension for macOS. When FUSE_DARWIN_ENABLE_EXTENSIONS is set to 1 , the utimens handler is called with three time stamps — the file’s access, modification, and backup time stamps. By default, the handler is called with the file’s access and modification time stamps.
Fix a bug in the statfs API extension for macOS and add missing fuse_lib_statfs$DARWIN() handler
Fix a bug in the threadid module that prevented several file system callback handlers from being invoked when using the module
Adapt fuse_clone_chan_fd_default() for macOS. On macOS, there is no need to associate new FUSE device file descriptors with the original ones.
Rename crtime (creation time) btime (birth time). This change does not affect ABI stability, but it requires code updates when compiling a file system with this release and the macOS API extensions being enabled.

Improve Swift support
- Enable Clang module support to improve interoperability with Swift
- Drop the GM type name prefix in Swift
- Make UserFileSystem.MoveOptions more idiomatic for Swift
- Add FileAttributeKey extension defining additional framework-specific attribute keys
- These changes have no affect on ABI stability, but they require code updates when compiling a file system with this release
Turn NSObject categories UserFileSystemLifecycle, UserFileSystemOperations, and UserFileSystemResourceForks into actual protocols
Remove unsupported exchangedata() callback handler. exchangedata() has been superseded by renamex_np() and has been unsupported since macOS 11. This change deprecates the corresponding delegate method.
```
- (BOOL)exchangeDataOfItemAtPath:(NSString *)path
                  withItemAtPath:(NSString *)otherPath
                           error:(NSError * _Nullable * _Nonnull)error
```