GO-FUSE

native bindings for the FUSE kernel module.

Highlights

• High speed: as fast as libfuse using the gc compiler for single threaded loads.

• Supports in-process mounting of different FileSystems onto subdirectories of the FUSE mount.

• Supports 3 interfaces for writing filesystems:

  • PathFileSystem: define filesystems in terms path names.
  • NodeFileSystem: define filesystems in terms of inodes.
  • RawFileSystem: define filesystems in terms of FUSE's raw wire protocol.

• Both NodeFileSystem and PathFileSystem support manipulation of true hardlinks.

• Includes two fleshed out examples, zipfs and unionfs.

Examples

• example/hello/main.go contains a 60-line "hello world" filesystem

• zipfs/zipfs.go contains a small and simple read-only filesystem for zip and tar files. The corresponding command is in example/zipfs/ For example,

  mkdir /tmp/mountpoint
  example/zipfs/zipfs /tmp/mountpoint file.zip &
  ls /tmp/mountpoint
  fusermount -u /tmp/mountpoint

• zipfs/multizipfs.go shows how to use in-process mounts to combine multiple Go-FUSE filesystems into a larger filesystem.

• fuse/loopback.go mounts another piece of the filesystem. Functionally, it is similar to a symlink. A binary to run is in example/loopback/ . For example

  mkdir /tmp/mountpoint
  example/loopback/loopback -debug /tmp/mountpoint /some/other/directory &
  ls /tmp/mountpoint
  fusermount -u /tmp/mountpoint

• unionfs/unionfs.go: implements a union mount using 1 R/W branch, and multiple R/O branches.

  mkdir -p  /tmp/mountpoint /tmp/writable
  example/unionfs/unionfs /tmp/mountpoint /tmp/writable /usr &
  ls /tmp/mountpoint
  ls -l /tmp/mountpoint/bin/vi
  rm /tmp/mountpoint/bin/vi
  ls -l /tmp/mountpoint/bin/vi
  cat /tmp/writable/DELETION/*

• union/autounionfs.go: creates UnionFs mounts automatically based on existence of READONLY symlinks.

Tested on:

• x86 32bits (Fedora 14).
• x86 64bits (Ubuntu Lucid).

Benchmarks

We use threaded stats over a read-only filesystem for benchmarking. Automated code is under benchmark/ directory. A simple C version of the same FS gives a FUSE baseline

Data points (Go-FUSE version May 2012), 1000 files, high level interface, all kernel caching turned off, median stat time:

platform libfuse Go-FUSE difference (%)

Lenovo T60/Fedora16 (1cpu) 349us 355us 2% slower Lenovo T400/Lucid (1cpu) 138us 140us 5% slower Dell T3500/Lucid (1cpu) 72us 76us 5% slower

On T60, for each file we have

• Client side latency is 360us
• 106us of this is server side latency (4.5x lookup 23us, 1x getattr 4us)
• 16.5us is due to latency measurements.
• 3us is due to garbage collection.

macOS Support

go-fuse works somewhat on OSX. Known limitations:

• All of the limitations of OSXFUSE, including lack of support for NOTIFY.

• OSX issues STATFS calls continuously (leading to performance concerns).

• OSX has trouble with concurrent reads from the FUSE device, leading to performance concerns.

• Tests are expected to pass; report any failure as a bug!

Credits

• Inspired by Taru Karttunen's package, https://bitbucket.org/taruti/go-extra.

• Originally based on Ivan Krasin's https://github.com/krasin/go-fuse-zip

Bugs

Yes, probably. Report them through https://github.com/nekojarashi/go-fuse/issues

Disclaimer

This is not an official Google product.

Known Problems

Grep source code for TODO. Major topics:

• Missing support for network FS file locking: FUSE_GETLK, FUSE_SETLK, FUSE_SETLKW

• Missing support for FUSE_INTERRUPT, CUSE, BMAP, IOCTL

• In the path API, renames are racy; See also:

  http://sourceforge.net/mailarchive/message.php?msg_id=27550667

  Don't use the path API if you care about correctness.

License

Like Go, this library is distributed under the new BSD license. See accompanying LICENSE file.

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Appendix I. Go-FUSE log format

To increase signal/noise ratio Go-FUSE uses abbreviations in its debug log output. Here is how to read it:

• iX means inode X;
• gX means generation X;
• tA and tE means timeout for attributes and directory entry correspondingly;
• [<off> +<size>) means data range from <off> inclusive till <off>+<size> exclusive;
• Xb means X bytes.

Every line is prefixed with either rx <unique> or tx <unique> to denote whether it was for kernel request, which Go-FUSE received, or reply, which Go-FUSE sent back to kernel.

Example debug log output:

rx 2: LOOKUP i1 [".wcfs"] 6b
tx 2:     OK, {i3 g2 tE=1s tA=1s {M040755 SZ=0 L=0 1000:1000 B0*0 i0:3 A 0.000000 M 0.000000 C 0.000000}}
rx 3: LOOKUP i3 ["zurl"] 5b
tx 3:     OK, {i4 g3 tE=1s tA=1s {M0100644 SZ=33 L=1 1000:1000 B0*0 i0:4 A 0.000000 M 0.000000 C 0.000000}}
rx 4: OPEN i4 {O_RDONLY,0x8000}
tx 4:     38=function not implemented, {Fh 0 }
rx 5: READ i4 {Fh 0 [0 +4096)  L 0 RDONLY,0x8000}
tx 5:     OK,  33b data "file:///"...
rx 6: GETATTR i4 {Fh 0}
tx 6:     OK, {tA=1s {M0100644 SZ=33 L=1 1000:1000 B0*0 i0:4 A 0.000000 M 0.000000 C 0.000000}}
rx 7: FLUSH i4 {Fh 0}
tx 7:     OK
rx 8: LOOKUP i1 ["head"] 5b
tx 8:     OK, {i5 g4 tE=1s tA=1s {M040755 SZ=0 L=0 1000:1000 B0*0 i0:5 A 0.000000 M 0.000000 C 0.000000}}
rx 9: LOOKUP i5 ["bigfile"] 8b
tx 9:     OK, {i6 g5 tE=1s tA=1s {M040755 SZ=0 L=0 1000:1000 B0*0 i0:6 A 0.000000 M 0.000000 C 0.000000}}
rx 10: FLUSH i4 {Fh 0}
tx 10:     OK
rx 11: GETATTR i1 {Fh 0}
tx 11:     OK, {tA=1s {M040755 SZ=0 L=1 1000:1000 B0*0 i0:1 A 0.000000 M 0.000000 C 0.000000}}