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Dobrica Pavlinušić


Fuse - write filesystems in Perl using FUSE


  use Fuse;
  my ($mountpoint) = "";
  $mountpoint = shift(@ARGV) if @ARGV;
  Fuse::main(mountpoint=>$mountpoint, getattr=>\&my_getattr, getdir=>\&my_getdir, ...);


This lets you implement filesystems in perl, through the FUSE (Filesystem in USErspace) kernel/lib interface.

FUSE expects you to implement callbacks for the various functions.

NOTE: I have only tested the things implemented in example.pl! It should work, but some things may not.

In the following definitions, "errno" can be 0 (for a success), -EINVAL, -ENOENT, -EONFIRE, any integer less than 1 really.

You can import standard error constants by saying something like "use POSIX qw(EDOTDOT ENOANO);".

Every constant you need (file types, open() flags, error values, etc) can be imported either from POSIX or from Fcntl, often both. See their respective documentations, for more information.


None by default.





Takes arguments in the form of hash key=>value pairs. There are many valid keys. Most of them correspond with names of callback functions, as described in section 'FUNCTIONS YOUR FILESYSTEM MAY IMPLEMENT'. A few special keys also exist:

debug => boolean

    This turns FUSE call tracing on and off. Default is 0 (which means off).

mountpoint => string

    The point at which to mount this filesystem. There is no default, you must specify this. An example would be '/mnt'.

unthreaded => boolean

    This turns FUSE multithreading off and on. NOTE: This perlmodule does not currently work properly in multithreaded mode! The author is unfortunately not familiar enough with perl-threads internals, and according to the documentation available at time of writing (2002-03-08), those internals are subject to changing anyway. Note that singlethreaded mode also means that you will not have to worry about reentrancy, though you will have to worry about recursive lookups (since the kernel holds a global lock on your filesystem and blocks waiting for one callback to complete before calling another).

    I hope to add full multithreading functionality later, but for now, I recommend you leave this option at the default, 1 (which means unthreaded, no threads will be used and no reentrancy is needed).



Arguments: filename. Returns a list, very similar to the 'stat' function (see perlfunc). On error, simply return a single numeric scalar value (e.g. "return -ENOENT();").

FIXME: the "ino" field is currently ignored. I tried setting it to 0 in an example script, which consistently caused segfaults.

Fields (the following was stolen from perlfunc(1) with apologies):

($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size, $atime,$mtime,$ctime,$blksize,$blocks) = getattr($filename);

Here are the meaning of the fields:

 0 dev      device number of filesystem
 1 ino      inode number
 2 mode     file mode  (type and permissions)
 3 nlink    number of (hard) links to the file
 4 uid      numeric user ID of file's owner
 5 gid      numeric group ID of file's owner
 6 rdev     the device identifier (special files only)
 7 size     total size of file, in bytes
 8 atime    last access time in seconds since the epoch
 9 mtime    last modify time in seconds since the epoch
10 ctime    inode change time (NOT creation time!) in seconds
            since the epoch
11 blksize  preferred block size for file system I/O
12 blocks   actual number of blocks allocated

(The epoch was at 00:00 January 1, 1970 GMT.)

Arguments: link pathname. Returns a scalar: either a numeric constant, or a text string.

This is called when dereferencing symbolic links, to learn the target.

example rv: return "/proc/self/fd/stdin";


Arguments: Containing directory name. Returns a list: 0 or more text strings (the filenames), followed by a numeric errno (usually 0).

This is used to obtain directory listings. Its opendir(), readdir(), filldir() and closedir() all in one call.

example rv: return ('.', 'a', 'b', 0);


Arguments: Filename, numeric modes, numeric device Returns an errno (0 upon success, as usual).

This function is called for all non-directory, non-symlink nodes, not just devices.


Arguments: New directory pathname, numeric modes. Returns an errno.

Called to create a directory.

Arguments: Filename. Returns an errno.

Called to remove a file, device, or symlink.


Arguments: Pathname. Returns an errno.

Called to remove a directory.

Arguments: Existing filename, symlink name. Returns an errno.

Called to create a symbolic link.


Arguments: old filename, new filename. Returns an errno.

Called to rename a file, and/or move a file from one directory to another.

Arguments: Existing filename, hardlink name. Returns an errno.

Called to create hard links.


Arguments: Pathname, numeric modes. Returns an errno.

Called to change permissions on a file/directory/device/symlink.


Arguments: Pathname, numeric uid, numeric gid. Returns an errno.

Called to change ownership of a file/directory/device/symlink.


Arguments: Pathname, numeric offset. Returns an errno.

Called to truncate a file, at the given offset.


Arguments: Pathname, numeric actime, numeric modtime. Returns an errno.

Called to change access/modification times for a file/directory/device/symlink.


Arguments: Pathname, numeric flags (which is an OR-ing of stuff like O_RDONLY and O_SYNC, constants you can import from POSIX). Returns an errno.

No creation, or trunctation flags (O_CREAT, O_EXCL, O_TRUNC) will be passed to open(). Your open() method needs only check if the operation is permitted for the given flags, and return 0 for success.


Arguments: Pathname, numeric requestedsize, numeric offset. Returns a numeric errno, or a string scalar with up to $requestedsize bytes of data.

Called in an attempt to fetch a portion of the file.


Arguments: Pathname, scalar buffer, numeric offset. You can use length($buffer) to find the buffersize. Returns an errno.

Called in an attempt to write (or overwrite) a portion of the file. Be prepared because $buffer could contain random binary data with NULLs and all sorts of other wonderful stuff.


Arguments: none Returns any of the following:



$namelen, $files, $files_free, $blocks, $blocks_avail, $blocksize


-ENOANO(), $namelen, $files, $files_free, $blocks, $blocks_avail, $blocksize


Mark Glines, <mark@glines.org>


perl, the FUSE documentation.