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SubjectRe: Multiplexing filesystem

Oh yeah. The MS Distributed File System in W2K is actually
a filter driver on top of their existings FS's. So is
the mail slot interface.


On Mon, Nov 26, 2001 at 09:34:38PM -0700, Jeff V. Merkey wrote:
> You may want to look at FS filter drivers in Windows 2000 as a good model
> for something like this. Intermezzo also seems to do something a lot
> like this, but not to the Windows 2000 degree. W2K has something
> called a filter driver interface, which is super handy for
> encryption, and going remote.
> The filter driver idea is pretty cool, and MS has been able to
> implement some pretty cool stuff with it, like snap in virus
> detection software across different file systems. They also
> did something called a "mini-port" file system, which was a
> filter driver on top of their very complex IFS interface which
> made writing remote file systems, like network clients, as lot
> easier and faster.
> The disadvantage to their approach was that several new
> and nasty "viruses" showed up as filter drivers and used
> this interface to trash file systems.
> Food for thought.
> :-)
> Jeff
> On Mon, Nov 26, 2001 at 10:59:48PM -0500, Mark Richards wrote:
> > Quick question, which I suspect has a long answer.
> >
> > I would like to write a multiplexing filesystem. The idea is as follows:
> >
> > The filesystem would ideally wrap another filesystem, such as nfs or smbfs or
> > ext2. Most operations would just be passed to the native fs call. However, for
> > some files, selectable at run time by some control singal, would actually reside
> > on another file system. The other filesystem would have to be mounted.
> >
> > The idea is for a version controlling filesystem. The server would be a network
> > server (hence the desire to wrap nfs) which presents a 'view' of the source
> > code. When the user reserves a file for editing, the file is copied to the
> > local disk. From that point on, the local file is referred to until the user
> > commits the change or unreserves the file. Ideally, the local copy of the file
> > could be on any file system, not one that is necessarily local. And this has to
> > be totally transparent to the user, except for the step where the user
> > 'reserves' the file.
> >
> > I've thought about two ways to do this. One is to wrap the 'versioning' file
> > system with a multiplexor that checks fs calls to see if they are referring to a
> > file that is on a different fs. The other approach is to intercept calls to the
> > VFS to do the same trick.
> >
> > I'm new to the whole filesystem-coding thing, so bear with me if what i've just
> > said makes no sense. So, my question (I guess it wasn't quick after all) is:
> > Can it be done, and are either of my two approaches feasible? Any suggestions
> > or tips?
> >
> > Thanks,
> > Mark Richards
> >
> > PS please CC me if possible.
> >
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