Apocalypse > POE-Component-Fuse-0.05 > POE::Component::Fuse

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Module Version: 0.05   Source  

NAME ^

POE::Component::Fuse - Using FUSE in POE asynchronously

SYNOPSIS ^

        #!/usr/bin/perl
        # a simple example to illustrate directory listings
        use strict; use warnings;

        use POE qw( Component::Fuse );
        use base 'POE::Session::AttributeBased';

        # constants we need to interact with FUSE
        use Errno qw( :POSIX );         # ENOENT EISDIR etc

        my %files = (
                '/' => {        # a directory
                        type => 0040,
                        mode => 0755,
                        ctime => time()-1000,
                },
                '/a' => {       # a file
                        type => 0100,
                        mode => 0644,
                        ctime => time()-2000,
                },
                '/foo' => {     # a directory
                        type => 0040,
                        mode => 0755,
                        ctime => time()-3000,
                },
                '/foo/bar' => { # a file
                        type => 0100,
                        mode => 0755,
                        ctime => time()-4000,
                },
        );

        POE::Session->create(
                __PACKAGE__->inline_states(),
        );

        POE::Kernel->run();
        exit;

        sub _start : State {
                # create the fuse session
                POE::Component::Fuse->spawn;
                print "Check us out at the default place: /tmp/poefuse\n";
                print "You can navigate the directory, but no I/O operations are supported!\n";
        }
        sub _child : State {
                return;
        }
        sub _stop : State {
                return;
        }

        # return unimplemented for the rest of the FUSE api
        sub _default : State {
                if ( $_[ARG0] =~ /^fuse/ ) {
                        $_[ARG1]->[0]->( -ENOSYS() );
                }
                return;
        }

        sub fuse_CLOSED : State {
                print "shutdown: $_[ARG0]\n";
                return;
        }

        sub fuse_getattr : State {
                my( $postback, $context, $path ) = @_[ ARG0 .. ARG2 ];

                if ( exists $files{ $path } ) {
                        my $size = exists( $files{ $path }{'cont'} ) ? length( $files{ $path }{'cont'} ) : 0;
                        $size = $files{ $path }{'size'} if exists $files{ $path }{'size'};
                        my $modes = ( $files{ $path }{'type'} << 9 ) + $files{ $path }{'mode'};
                        my ($dev, $ino, $rdev, $blocks, $gid, $uid, $nlink, $blksize) = ( 0, 0, 0, 1, (split( /\s+/, $) ))[0], $>, 1, 1024 );
                        my ($atime, $ctime, $mtime);
                        $atime = $ctime = $mtime = $files{ $path }{'ctime'};

                        # finally, return the darn data!
                        $postback->( $dev, $ino, $modes, $nlink, $uid, $gid, $rdev, $size, $atime, $mtime, $ctime, $blksize, $blocks );
                } else {
                        # path does not exist
                        $postback->( -ENOENT() );
                }

                return;
        }

        sub fuse_getdir : State {
                my( $postback, $context, $path ) = @_[ ARG0 .. ARG2 ];

                if ( exists $files{ $path } ) {
                        if ( $files{ $path }{'type'} & 0040 ) {
                                # construct all the data in this directory
                                my @list = map { $_ =~ s/^$path\/?//; $_ }
                                        grep { $_ =~ /^$path\/?[^\/]+$/ } ( keys %files );

                                # no need to add "." and ".." - FUSE handles it automatically!

                                # return the list with a success code on the end
                                $postback->( @list, 0 );
                        } else {
                                # path is not a directory!
                                $postback->( -ENOTDIR() );
                        }
                } else {
                        # path does not exist!
                        $postback->( -ENOENT() );
                }

                return;
        }

        sub fuse_getxattr : State {
                my( $postback, $context, $path, $attr ) = @_[ ARG0 .. ARG3 ];

                # we don't have any extended attribute support
                $postback->( 0 );

                return;
        }

ABSTRACT ^

Using this module will enable you to asynchronously process FUSE requests from the kernel in POE. Think of this module as a simple wrapper around Fuse to POEify it.

DESCRIPTION ^

This module allows you to use FUSE filesystems in POE. Basically, it is a wrapper around Fuse and exposes it's API via events. Furthermore, you can use Filesys::Virtual to handle the filesystem.

The standard way to use this module is to do this:

        use POE;
        use POE::Component::Fuse;

        POE::Component::Fuse->spawn( ... );

        POE::Session->create( ... );

        POE::Kernel->run();

Naturally, the best way to quickly get up to speed is to study other implementations of FUSE to see what they have done. Furthermore, please look at the scripts in the examples/ directory in the tarball!

Starting Fuse

To start Fuse, just call it's spawn method:

        POE::Component::Fuse->spawn( ... );

This method will return failure on errors or return success.

NOTE: The act of starting/stopping PoCo-Fuse fires off _child events, read the POE documentation on what to do with them :)

This constructor accepts either a hashref or a hash, valid options are:

alias

This sets the session alias in POE.

The default is: "fuse"

mount

This sets the mountpoint for FUSE.

If this mountpoint doesn't exist ( and the "mkdir" option isn't set ) spawn() will return failure.

The default is: "/tmp/poefuse"

mountoptions

This passes the options to FUSE for mounting.

NOTE: this is a comma-separated string!

The default is: undef

mkdir

If true, PoCo-Fuse will attempt to mkdir the mountpoint if it doesn't exist.

If the mkdir attempt fails, spawn() will return failure.

The default is: false

umount

If true, PoCo-Fuse will attempt to umount the filesystem on exit/shutdown.

This basically calls "fusermount -u -z $mountpoint"

WARNING: This is not exactly portable and is in the testing stage. Feedback would be much appreciated!

The default is: false

rmdir

If true, PoCo-Fuse will attempt to rmdir the mountpoint on exit/shutdown. Extremely useful when you specify a mountpoint that was randomly-generated ( e.x. "/tmp/poe$$" ) so we don't "leave behind" lots of empty directories.

WARNING: Be careful when using this or your directory could vanish!

prefix

The prefix for all events generated by this module when using the "session" method.

The default is: "fuse_"

session

The session to send all FUSE events to. Used in conjunction with the "prefix" option, you can control where the events arrive.

If this option is missing ( or POE is not running ) and "vfilesys" isn't enabled spawn() will return failure.

NOTE: You cannot use this and "vfilesys" at the same time! PoCo-Fuse will pick vfilesys over this! If this is the case, then the session will only get the CLOSE event, not API requests.

The default is: calling session ( if POE is running ) when "vfilesys" isn't specified or error

vfilesys

The Filesys::Virtual object to use as our filesystem. PoCo-Fuse will proceed to use Fuse::Filesys::Virtual to wrap around it and process the events internally.

Furthermore, you can also use Filesys::Virtual::Async subclasses, this module understands their callback API and will process it properly!

If this option is missing and "session" isn't enabled spawn() will return failure.

NOTE: You cannot use this and "session" at the same time! PoCo-Fuse will pick this over session!

Compatibility has not been tested with all Filesys::Virtual::XYZ subclasses, so please let me know if some isn't working properly!

The default is: not used

Commands

There is only one command you can use, because this module does nothing except process FUSE events.

shutdown

Tells this module to kill the FUSE mount and terminates the session. Due to the semantics of FUSE, this will often result in a wedged filesystem. You would need to either umount it manually ( via "fusermount -u $mount" ) or by enabling the "umount" option.

Events

If you aren't using the Filesys::Virtual interface, the FUSE api will be exposed to you in it's glory via events to your session. You can process them, and send the data back via the supplied postback. All the arguments are identical to the one in Fuse so please take a good look at that module for more information!

The only place where this differs is the additional arguments. All events will receive 2 extra arguments in front of the standard FUSE args. They are the postback and context info. The postback is self-explanatory, you supply the return data to it and it'll fire an event back to PoCo-Fuse for processing. The context is the calling context received from FUSE. It is a hashref with the 3 keys in it: uid, gid, pid. It is received via the fuse_get_context() sub from Fuse.

Remember that the events are the fuse methods with the prefix tacked on to them. A typical FUSE handler would look something like the example below. ( it is sugared via POE::Session::AttributeBased hah )

        sub fuse_getdir : State {
                my( $postback, $context, $path ) = @_[ ARG0 .. ARG2 ];

                # somehow get our data, we fake it here for instructional reasons
                $postback->( 'foo', 'bar', 0 );
                return;
        }

Again, pretty please read the Fuse documentation for all the events you can receive. Here's the list as of Fuse v0.09: getattr readlink getdir mknod mkdir unlink rmdir symlink rename link chmod chown truncate utime open read write statfs flush release fsync setxattr getxattr listxattr removexattr.

CLOSED

This is a special event sent to the session notifying it of component shutdown. As usual, it will be prefixed by the prefix set in the options.

The event handler will get one argument, the error string. If you shut down the component, it will be "shutdown", otherwise it will contain some error string. A sample handler is below.

        sub fuse_CLOSED : State {
                my $error = $_[ARG0];
                if ( $error ne 'shutdown' ) {
                        print "AIEE: $error\n";

                        # do some actions like emailing the sysadmin, restarting the component, etc...
                } else {
                        # we told it to shutdown, so what do we want to do next?
                }

                return;
        }

Internals

XSification

This module does it's magic by spawning a subprocess via Wheel::Run and passing events back and forth to the Fuse module loaded in it. This isn't exactly optimal which is obvious, but it works perfectly!

I'm working on improving this by using XS but it will take me some time seeing how I'm a n00b :( Furthermore, FUSE doesn't really help because I have to figure out how to get at the filehandle buried deep in it and expose it to POE...

If anybody have the time and knowledge, please help me out and we can have fun converting this to a pure XS module!

Debugging

You can enable debug mode which prints out some information ( and especially error messages ) by doing this:

        sub POE::Component::Fuse::DEBUG () { 1 }
        use POE::Component::Fuse;

EXPORT ^

None.

SEE ALSO ^

POE

Fuse

Filesys::Virtual

Fuse::Filesys::Virtual

Filesys::Virtual::Async

SUPPORT ^

You can find documentation for this module with the perldoc command.

    perldoc POE::Component::Fuse

Websites

Bugs

Please report any bugs or feature requests to bug-poe-component-fuse at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=POE-Component-Fuse. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

AUTHOR ^

Apocalypse <apocal@cpan.org>

Props goes to xantus who got me motivated to write this :)

Also, this module couldn't have gotten off the ground if not for Fuse which did the heavy XS lifting!

COPYRIGHT AND LICENSE ^

Copyright 2009 by Apocalypse

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

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