Filesys::Virtual::Async::inMemory - Mount filesystems that reside in memory ( sort of ramfs )


        use strict; use warnings;
        use Fcntl qw( :DEFAULT :mode ); # S_IFREG S_IFDIR, O_SYNC O_LARGEFILE etc

        # uncomment this to enable debugging
        #sub Filesys::Virtual::Async::inMemory::DEBUG { 1 }

        use Filesys::Virtual::Async::inMemory;

        # create the filesystem
        my $vfs = Filesys::Virtual::Async::inMemory->new(
                'filesystem'    => {
                        '/'     => {
                                mode => oct( '040755' ),
                                ctime => time(),

        # use $vfs as you wish!
        $vfs->readdir( '/', sub {       # should print out nothing
                my $data = shift;
                if ( defined $data ) {
                        foreach my $e ( @$data ) {
                                print "entry in / -> $e\n";
                        print "end of listing for /\n";
                } else {
                        print "error reading /\n";
        } );

        my $fh;
        sub do_file_io {
                $vfs->mknod( '/bar', oct( '100644' ), 0, \&did_mknod );
        sub did_mknod {
                if ( $_[0] == 0 ) {
                        # write to it!
                        $vfs->open( '/bar', O_RDWR, 0, \&did_open );
                } else {
                        print "error mknod /bar\n";
        sub did_open {
                $fh = shift;
                if ( defined $fh ) {
                        my $buf = "foobar";
                        $vfs->write( $fh, 0, length( $buf ), $buf, 0, \&did_write );
                } else {
                        print "error opening /bar\n";
        sub did_write {
                my $wrote = shift;
                if ( $wrote ) {
                        print "successfully wrote to /bar\n";
                        $vfs->close( $fh, \&did_close );
                } else {
                        print "error writing to /bar\n";
        sub did_close {
                my $status = shift;
                if ( $status == 0 ) {
                        print "successfuly closed fh\n";
                } else {
                        print "error in closing fh\n";


Using this module will enable you to have "ramfs" filesystems in the Filesys::Virtual::Async API.


This module lets you run the Filesys::Virtual::Async API entirely in memory. Nothing special here, really :)

This module makes extensive use of the functions in File::Spec to be portable, so it might trip you up if you are developing on a linux box and trying to play with '/foo' on a win32 box :)

Initializing the vfs

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


This sets the "filesystem" that we will have in memory. It needs to be a particular structure!

If this argument is missing, we will create an empty filesystem.


This enables readonly mode, which will prohibit any changes to the filesystem.

The default is: false


This sets the "current working directory" in the filesystem.

The default is: File::Spec->rootdir()



Enables/disables readonly mode. This is also an accessor.

Special Cases

This module does a good job of covering the entire ::Async API, but there are some areas that needs mentioning.


Unimplemented, No sense in changing the root during run-time...


Array mode not supported because it would require extra munging on my part to get the paths right.


Links are not supported at this time because of the complexity involved.


Always returns success ( 0 ), because they are useless to us

Subclassing this module

If you want to subclass this module, please read on! The primary reason for subclassing is so you have true "callbacks" whenever the API is called, instead of providing a static filesystem structure. This module tries to do it's best to reduce the pain, but you would need to be aware of some things.

The way this module implements subclassing is to call a private method whenever it detects a subclass using this module as a superclass. Please don't override the ::Async API! What you need to do is define your own _method subs for the ones you want to override. All other methods that aren't defined will return ENOSYS to the ::Async API.

Available methods to implement: _rmtree, _scandir, _move, _copy, _load, _readdir, _rmdir, _mkdir, _rename, _mknod, _unlink, _chmod, _truncate, _chown, _utime, _stat, _write, _open.

Again, please look at the source for this module to see how it interacts with the subclass. Some of the methods have been "simplified" to reduce the pain of managing the data. Be sure to let this module create the object, because we need the "readonly" attribute to be present in the hash! If "readonly" is set, this module will take over the logic for certain methods and not call your method if there's a readonly violation ( write(), for example ).


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

        sub Filesys::Virtual::Async::inMemory::DEBUG () { 1 }
        use Filesys::Virtual::Async::inMemory;


  • automatically overriding CORE::* methods

            <buu> Apocalypse: Hey, while you're at it, can you make it so all file access operators in perl operate on virtual directories?
            <Apocalypse> buu: hm you mean overriding readdir(), stat()?
            <buu> Yes.
            <Apocalypse> as of now you would have to explicitly use the filesys::virtual::async::inmemory object and do operations on it -> $fsv->readdir(), $fsv->open(), etc
            <buu> But I don't want to!
            <buu> =]
            <Apocalypse> but that would be a fun side project to try and figure out how to hijack CORE:: stuff
            <buu> Yes!
            <Apocalypse> hmm you could locally scope the hijack, pass a $fsv object to the module init, and have it transparently replace all file operations in the scope with $fsv->method calls
            <Apocalypse> why would you want it? pure laziness? haha
            <buu> Apocalypse: For buubot..
            <Apocalypse> mmm for now you can just use fsv::inmemory until somebody with enough wizardry does the overrides :)
            <Apocalypse> I'll file that away in my TODO and see if I will return to it someday hah
            <buu> Exccelent.




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

    perldoc Filesys::Virtual::Async::inMemory



Please report any bugs or feature requests to bug-filesys-virtual-async-inmemory at, or through the web interface at I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.


Apocalypse <>

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


Copyright 2010 by Apocalypse

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