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[Dazuko-devel] RedirFS and Dazuko Filter

From: Frantisek Hrbata
Subject: [Dazuko-devel] RedirFS and Dazuko Filter
Date: Tue, 28 Feb 2006 18:18:28 +0100


it has been a while since my last post to this mailing list about RedirFS.
In spite of that John Ogness did not like the idea of replacing(hooking) VFS 
object operations
I kept on working on RedirFS and I started the RedirFS project. Because I have 
made some progress
and the first testing version is available for public I would like to tell you 
few things about
the RedirFS project and about the Dazuko Filter.

RedirFS stands for Redirecting FileSystem. It is implemented as a Linux Kernel 
Module(LKM) and creates a new
layer between Linux Virtual Filesystem Switch(VFS) and native filesystem 
drivers(EXT2, NFS, etc.). It is based
on replacing VFS object operations and its main purpose is to make native 
filesystem calls accessible
to 3rd-party LKM.

Here is a list of RedirFS's basic features:
* Implemented as a LKM that does not need to modify Linux kernel source code.
* For now it works only with 2.6.x kernels. Back-port to 2.4.x kernels should 
be not difficult.
* Allows to manage one or more Filters(3rd-party LKMs) and call them in 
specific order based on their priorities.
* Allows Filters to select pre and post callback function for selected native 
filesystem call.
* Allows Filters to include or exclude directories over which their callback 
function will be called or not.
* It redirects only operations which are required by Filters. All other calls 
goes directly to native filesystem
  drivers with absolutely no overhead. If redirected operation is no longer 
used by any Filter it is set back to original
* Only VFS objects which belong to directories selected by Filters are affected.
* Allows Filters on-the-fly to set, reset and remove callback functions.
* Allows Filters on-the-fly to include and exclude directories.
* Filters can be dynamically added and removed.
* For now only selected operations for regular files, directories and dentries 
can be redirected.
* For now it ignores sub-mounts, so you have to explicitly include them.

- RedirFS was tested on x86(i386) and x86_64 architectures.
- Do NOT try to include /proc directory(/proc directory has different 
operations then its subdirs)
- It is strongly recommended to use RedirFS only on testing machines where 
filesystem violation is acceptable.

Dazuko Filter uses the RedirFS Framework to get necessary events from Linux 

Dazuko Filter features:
* available as a patch for Dazuko 2.1.0
* allows Dazuko to generate ON_OPEN, ON_EXEC, ON_CLOSE, ON_RMDIR and ON_UNLINK 

For more information please see the RedirFS project site at www.redirfs.org.

RedirFS INSTALL file - 
Dazuko Filter INSTALL file - 

RedirFS is intended as a general framework which will allow to redirect all 
operations in VFS objects.
I think that a lot of interesting Filters can be written using the RedirFS 
Framework(e.g. UnionFS, 
CompressFS, CryptographicFS, ACLs etc.)

I will be thankful for all your feedbacks.

Frantisek Hrbata

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