ocamlfuse

OCaml bindings for FUSE (Filesystem in UserSpacE)
README

This repository is cloned from the last CVS snapshot of
OCamlFuse, with:

  • Patches (see #1 and #3) to make it compile on Mac OS X.

  • Fix for a race condition in multi-threaded mode (see #4).

  • dune support (see #12).

INTRODUCTION

This is a binding to fuse for the ocaml programming language, enabling
you to write multithreaded filesystems in the ocaml language. It has
been designed with simplicity as a goal, as you can see by looking at
example/fusexmp.ml. Efficiency has also been a separate goal. The
Bigarray library is used for read and writes, allowing the library to
do zero-copy in ocaml land.

REQUIREMENTS

You need fuse (version 2.7 or greater)

http://www.sourceforge.net/projects/fuse

You also need ocaml >= 4.02.3 and camlidl >= 1.05.

GETTING STARTED

The reccomended way to install this library is using
OPAM.

opam install ocamlfuse

INSTALLATION

If you don't want to install OPAM, you need to manually install this
prerequisites:

  1. Prerequisites

  • Fuse

    Should be in the major linux distributions, but you can find it at

    https://fuse.sourceforge.net

    You need to install libfuse-dev in debian and ubuntu.

  • OCaml >= 4.02.3

    Should be there in the major linux distributions, but is also available at

    https://www.ocaml.org

  • CamlIDL >= 1.05

    present at least in ubuntu, also available at

    https://github.com/xavierleroy/camlidl

  • dune >= 1.6

    available at

    https://dune.build/

  1. Installing OCamlFuse

unpack the tarball, then

make
make install

This will install ocamlfuse in your ocaml library directory. To uninstall
it you can use "make uninstall"

TESTING

make example
cd _build/default/example
mkdir tmp
./fusexmp.exe tmp
cd tmp #you'll find a copy of your "/" directory here

NOTE: if you access the "clone" of the mountpoint of the filesystem, the fs will hang (kill it and then use fusermount -u to umount it). This is a known bug/limitation.

BEFORE YOU WRITE YOUR OWN FILESYSTEM

KNOWN PROBLEMS (if you can help, please do)

  • The stateful interface for readdir is not implemented

  • There is a stub in Fuse_util.c regarding st_blocks - if one
    implements statfs with a block size different
    than 512 "du" will not work on the filesystem.

  • many ocaml exceptions are reported as 127

  • we should add non-blocking lstat64 and statfs,*xattr implementations for
    ocaml in Unix_util

  • translation between ocaml unix errors and C unix error is dependent
    on the order of constructor names in ocaml. There should be a way to
    get error names from caml and create a translation table.

  • the Unix_util library uses unsafe coercions between unix file
    handles (which are defined as ints) and ints. Even if this works, in
    the future it might stop working.

  • IMPORTANT: Unix_util.read and write operations have not been tested
    in case of errors. Error code conversion might be incorrect but I
    don't have test cases (maybe the easy way is to modify fusexmp to
    return various errors).

  • Unix errors which are unknown to ocaml should be reported as EUNKNOWNERR

  • Test statfs (never used until now)

  • Some errors are missing in the unix module (e.g. ENOTSUP,ENOATTR,
    see man lsxattr). We could solve all these problems with errors using
    a custom error type instead of unix_error but this would create
    troubles.

  • deadlock (and consequent necessity to kill -KILL the program) if
    accessing the mountpoint mirrored inside the mountpoint in
    fusexmp. I remember it was easy to understand why, but right now I
    have no idea.

HELPING THE PROJECT

The best help you can give to the project is to test everything,
including, but not limited to:

  • large file operations (files >= 4gb)

  • multithreaded operations: the filesystem should always be responsive,
    no matter if reading a certain file blocks

  • robustness: the filesystem should NEVER exit from its mainloop if not
    explicitly requested from the user.

Please report if you do serious tests! We need to know which programs
did you use, if you found any bug, and how to reproduce the tests.

Also, we need packaging, I don't have the necessary time and don't know
ocamlfindlib or GODI. Please if you have the time and the necessary
knowledge help with packaging. Autoconf support would be highly appreciated,
too.

A mailing list has been set up on sourceforge, you are strongly
encouraged to post feedback there and in general to subscribe if you use ocamlfuse.

The sourceforge page for ocamlfuse is

http://sourceforge.net/projects/ocamlfuse

Bye and have fun

Vincenzo Ciancia

vincenzo_ml at yahoo dot it
ciancia at di dot unipi dot it
applejack at users dot sourceforge dot net