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Fuse - write filesystems in Perl using FUSE


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

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.

You can request all exportable symbols by using the tag ":all".

You can request the extended attribute symbols by using the tag ":xattr". This will export XATTR_CREATE and XATTR_REPLACE.



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'.

mountopts => string

    This is a comma seperated list of mount options to pass to the FUSE kernel module.

    At present, it allows the specification of the allow_other argument when mounting the new FUSE filesystem. To use this, you will also need 'user_allow_other' in /etc/fuse.conf as per the FUSE documention

      mountopts => "allow_other" or
      mountopts => ""

threaded => boolean

    This turns FUSE multithreading on and off. The default is 0, meaning your FUSE script will run in single-threaded mode. Note that single-threaded mode also means that you will not have to worry about reentrancy, though you will have to worry about recursive lookups. In single-threaded mode, FUSE holds a global lock on your filesystem, and will wait for one callback to return before calling another. This can lead to deadlocks, if your script makes any attempt to access files or directories in the filesystem it is providing. (This includes calling stat() on the mount-point, statfs() calls from the 'df' command, and so on and so forth.) It is worth paying a little attention and being careful about this.

    Enabling multithreading will cause FUSE to make multiple simultaneous calls into the various callback functions of your perl script. If you enable threaded mode, you can enjoy all the parallel execution and interactive response benefits of threads, and you get to enjoy all the benefits of race conditions and locking bugs, too. Please also ensure any other perl modules you're using are also thread-safe.

    (If enabled, this option will cause a warning if your perl interpreter was not built with USE_ITHREADS, or if you have failed to use threads or threads::shared.)



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


Arguments: Pathname Returns an errno or 0 on success.

Called to synchronise any cached data. This is called before the file is closed. It may be called multiple times before a file is closed.


Arguments: Pathname, numeric flags passed to open Returns an errno or 0 on success.

Called to indicate that there are no more references to the file. Called once for every file with the same pathname and flags as were passed to open.


Arguments: Pathname, numeric flags Returns an errno or 0 on success.

Called to synchronise the file's contents. If flags is non-zero, only synchronise the user data. Otherwise synchronise the user and meta data.


Arguments: Pathname, extended attribute's name, extended attribute's value, numeric flags (which is an OR-ing of XATTR_CREATE and XATTR_REPLACE Returns an errno or 0 on success.

Called to set the value of the named extended attribute.

If you wish to reject setting of a particular form of extended attribute name (e.g.: regexps matching user\..* or security\..*), then return - EOPNOTSUPP.

If flags is set to XATTR_CREATE and the extended attribute already exists, this should fail with - EEXIST. If flags is set to XATTR_REPLACE and the extended attribute doesn't exist, this should fail with - ENOATTR.

XATTR_CREATE and XATTR_REPLACE are provided by this module, but not exported by default. To import them:

    use Fuse ':xattr';


    use Fuse ':all';


Arguments: Pathname, extended attribute's name Returns an errno, 0 if there was no value, or the extended attribute's value.

Called to get the value of the named extended attribute.


Arguments: Pathname Returns a list: 0 or more text strings (the extended attribute names), followed by a numeric errno (usually 0).


Arguments: Pathname, extended attribute's name Returns an errno or 0 on success.


Mark Glines, <>


perl, the FUSE documentation.