Re: Work on ext3 extensions to ext2fs

[Jeff Read <bitwize%gmail.com@localhost>]

On Tue, Feb 4, 2014 at 10:39 AM, Pedro Giffuni <pfg%freebsd.org@localhost> 
wrote:
> Hi Jeff;
>
> Very interesting project. I think a couple of people had a try on adding
> journalling for ext2 on the BSDs and failed but it should be somewhat easier
> to do by taking a look at what NetBSD has done with UFS.
> It's still not straightforward though as the journal format differs.

Yes, As I recall there was a GSoC project in 2008 or so to add
journalling support to ext3 by porting WAPBL, but it fell on
difficulty and was not worked on. In addition to format differences,
jbd (Linux's ext3 journalling layer) supports things that WAPBL does
not, from what I've read; WAPBL does only metadata journalling whereas
jbd can also journal actual file blocks. So my approach has been to
write a journalling layer specifically for the ext2fs file system that
does the same things jbd does; for now I call it simply
ext3fs_journal.

> Feel free to take a look at the stuff we have done in FreeBSD:
>
> https://wiki.freebsd.org/Ext2fs
>
> We gave up on journalling in general, but so far the FreeBSD port is similar
> enough to NetBSD's code that we brought the dirindex implementation
> (originally developed as a GSoC for NetBSD).
>

I like the idea of having ext3fs and ext4fs features being extensions
to ext2fs, rather than separate fs drivers. It's broadly more
reflective of the upwardly extensible nature of the ext2 format, and
it's what I've chosen to do with ext3fs_journal.

The dirindex stuff may prove useful; I currently do not see support
for it in mainline NetBSD.

--Jeff