On 2011-02-07, at 08:19, Jan Kara wrote:

On Fri 04-02-11 10:36:21, Andreas Dilger wrote:

quoted

The question is whether we need to mimic the runtime behavior or just the
on-disk format?  Apps already need to deal with ext4 and other fs that do
not do ext3 ordered mode.

 Well written apps do, but badly written apps don't and e.g. our distro
customers don't always have the choice of the application. So as a developer
I see your point (screw stupidly written apps) but in the real world, I'm
afraid it's too hard on users.

We have to remember that this is only for new kernels, and does not affect older kernels or existing applications, so such users shouldn't be affected.

quoted

I think the best road forward is to make ext4 the default for ext2 and
ext3 filesystems in newer kernels, and mark ext2 and ext3 obsolete. This
will start to get usage and testing of these other config options. The
ext2 mode is already heavily tested at Google, and don't they also test
noextent mode on updated filesystems, or were all of the filesystems
reformatted with ext4 options?

 Yes, I know you are on relatively radical side ;). My position would be
to test ext4 for resonable combinations of options as ext2 driver and if
that works, switch ext2 as you describe. Then if it works fine for an year
or so, we can talk about ext3 but as James said, ext3 is still widely used
so there might be more friction on subtle runtime differences...

Since most new distros use ext4 by default, the point is kind of moot, because those users will get this behaviour in any case.  Relatively few users upgrade their kernel on a production system after it is installed, except for errata kernels, and I definitely wouldn't expect such a change to appear in an errata kernel.

Cheers, Andreas