GSoC proposition: multiplatform UFS2 driver

[Richard Yao]

On 03/13/2014 06:12 PM, Julio Merino wrote:
> On Fri, Mar 14, 2014 at 2:48 AM, Richard Yao <ryao at gentoo.org> wrote:
>> On 03/12/2014 12:54 PM, CeDeROM wrote:
>>> My proposition is to create universal UFS2 driver that would work on
>>> Windows, Linux, and maybe other OS, so we can use native UFS2 as data
>>> partition among various OS.
>>>
>>
>> I like this idea. In particular, I would like to have UFS2 SU+J
>> available for use in certain Linux VMs and was thinking about this
>> possibility earlier in the week. However, I no longer qualify to be a
>> GSoC student and I do not have time to do it myself.
>> [...]
>> Speaking as a kernel filesystem hacker (with most of my experience in
>> Linux), I think this could be too ambitious depending on how you add
>> detail. In particular, Linux has a moving target of a VFS (which causes
>> much pain) and Windows' IFS is very different from the SunOS VFS that
>> has become the basis for implementing multiple filesystems on different
>> UNIX implementations and copy-cats.
> [...]
> 
> Something worth pointing out here: in NetBSD, and thanks to rump, you
> can already get the *verbatim* in-kernel code of UFS2 built on a
> variety of host platforms. You could very easily turn the existing
> file system code into a FUSE file-system for Linux, for example, or
> write the necessary shims to bundle the code into a kernel driver.

This would work, but I think it dramatically reduces the value of the
result.

> In other words and in my opinion: rewriting file system code from
> scratch is outside of the scope of GSoC, but writing the glue code for
> the above to happen doesn't sound too crazy. (The only problem may be
> if NetBSD's UFS2 driver is not compatible with FreeBSD's... but I
> believe they should be for the "basic stuff".)
> 
> Some links:
> 
> https://github.com/rumpkernel/buildrump.sh
> http://wiki.netbsd.org/rumpkernel/
> 

There is no need to write the code from scratch. He would just need to
take the existing code and wrap it so that it builds as part of a kernel
module for other kernels. The only things that need to be written is
glue code for mapping *BSD interfaces to foreign ones. I do not think it
is much more complex than writing a FUSE filesystem driver, especially
given the existence of user-mode Linux. That would permit the filesystem
driver for Linux to be developed in userland on FreeBSD, much like a
FUSE driver. Once the wrapper is written, the things that need revision
to support other kernels should be rather clearly defined.

http://user-mode-linux.sourceforge.net/

That being said, I do not like the idea of using NetBSD's UFS2 code. It
lacks Soft-Updates, which I consider to make FreeBSD UFS2 second only to
ZFS in desirability.

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