Re: [Dazuko-devel] dazukoFS - redirFS

[Frantisek Hrbata]

On Wed, 6 Apr 2005, John Ogness wrote:

> Hi Franta,
>
> If we were go ahead with VFS object duplication, and you were to make it for
> Linux 2.6 only, how small could it be? I have looked around at lots of
> examples (including the code generated from FiST) and it seems like there is
> an enormous amount to keep track of. It also seems like there are a lot of
> behavior and structural changes from each kernel version.
>
> But if you were to take the current 2.6 Linux kernel and specialize a
> solution (based on VFS object duplication), how small and clean could you
> make it?

Annoying thing is, that we will have to take care of whole file system,
just to be able to catch some VFS events. Even if we will specialize our
transparent file system (dazukoFS) only for Linux kernels 2.6, there will
be still a lot of code, that we will have to maintain. Differences in the
VFS between kernels 2.2 to 2.6 are not  so big and I am afraid that
solution only for 2.6 kernels will not make the code smaller. With the
specialized file system for the 2.6 kernels we can only avoid some
portability problems. For these reasons I think we should use the FiST.
(even if it will require some maintenance from our side). Writing whole
file system from scratch is a lot of work and the code probably will not
be so much better than the code generated by FiST. Moreover with FiST it
will be portable to FreeBSD and Solaris.

> I know that you have done a lot of investigation on this, so I consider you
> to be the best qualified to answer.
>
> (I was quite impressed with how small and clean your redirfs was. I don't
> have any problems with the implementation. My problems stem from the general
> concept of "hacking" the VFS objects of other filesystems.)

You are right, redirfs is a hack to the Linux VFS. But I hope it should
solve a lot of problems. I know that there is no chance how to get this to
the vanilla kernel, but I'm going to keep working on it (even if it will
be only part of my thesis :)).

I'm still interested in dazukoFS, so if you think, that the overlay file
system has a chance to get to the Linux kernel, I will help.