Re: [Dazuko-devel] nullfs 0.0.2 posted

[John Ogness]

On 2008-04-27, jim burns <address@hidden> wrote:
> Well, that lets me out on fedora 8, which is still on 2.6.24, or
> SuSE 10.3, which is on 2.6.22. I could test it on my Fedora Rawhide
> (currently 9.01) xen domu tho'.

Yes, I realize that keeping up with HEAD of Linux development will
leave out people that stick to distro-kernels. If I track which
versions of nullfs worked with which kernel versions, users (in the
future) could use older nullfs versions with their distro-kernels.

But right now nullfs if for people that are willing to compile to
latest stable kernel from kernel.org.

> I haven't downloaded the code yet - waiting for it to be integrated
> into a new 3.x release.

Now that I have experienced the stability of nullfs, I am quite
excited about posting a new Dazuko 3.x pre-release based on it.

> Looking at your fstab, the question comes up does nullfs have the
> same problem 3.0/Fist had that you can't overlay '/' because of
> 'init'?

It is not possible to overlay '/' the way that sub-directories are
overlayed. In order to support overlaying '/', nullfs will need to
support sub-mounts. For example, in /etc/fstab it would look something
like this:

/dev/hda1   /   nullfs   submount='type=ext3,defaults'   0   1

When mounting '/', the type would be "nullfs" but nullfs would first
mount '/' as ext3 directly underneath it. This not only allows '/' to
be overlayed, but also makes it possible to use nullfs with
auto-mounters. It also eliminates the "risk" of processes being able
to access the mount underneath nullfs.

However, this is simply an idea, which is not planned for the initial
release. Supporting sub-mounts is significantly more difficult. For
example, nullfs would have to support things like:

# mount -o remount,ro /

I first would like to to get nullfs accepted as a
sub-directory-overlay. Then I can start looking into supporting
sub-mounts.

John Ogness

-- 
Dazuko Maintainer