Re: [gentoo-dev] Re: rfc: locations of binaries and separate /usr

[William Hubbs <williamh@gentoo.org>]

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On Sun, Jan 01, 2012 at 09:23:11AM +0000, Duncan wrote:
> Gentoo has historically been both "light patch", with a policy of staying 
> close to upstream if possible, and "customizer's choice", allowing users 
> far more flexibility than most distros.  Keeping both goals in mind, 
> migrating with upstream is ultimately the only viable alternative for a 
> whole host of reasons including both staying close to upstream and simple 
> manpower resource issues.

> That said, we can continue to try to support a separate /usr as long as 
> possible, while switching new installs to the new way and changing the 
> handbook to document it, preferably as soon as possible.

In this situation, I don't know how we will be able to support both
ways because there is more involved than just where things are
installed.

Udev 175 is currently masked, because  the way it operates has changed
enough that it doesn't work correctly if it starts before /usr is
mounted, and the failures you find will be very difficult to track down.
So, udev isn't only changing where it is installed, but how it runs.

Supporting a separate /usr without an initramfs will require one of two
things.

One possibility is a customization to openrc, which we have been
looking at, that would be able to run fsck on /usr and mount /usr all
before udev starts. The drawback here is this will only work for openrc
users.

Another possibility is a script that would run as the init= parameter to
the kernel, which would fsck /usr and mount /usr then start the real
init process. This would be more generic and would be able to run
regardless of whether you are using sysvinit/openrc.

Here is the big problem with both of these solutions as I see them. They
depend on several pieces of software remaining on the root filesystem,
and if/when this software is migrated, we will be back to having this discussion
again.

> Further, as 
> previously discussed, a near-static bare-minimal initramfs that can be 
> configured and forgotten about for long periods over many kernel upgrades 
> should make the switch as painless as possible at least for "simple" bare-
> partition installations.

I want to look at dracut and see if there is a way to configure it to
create a minimal initramfs like you are suggesting, because, if there is
we don't need to re-invent the wheel.

I don't think your portage feature/use flag suggestion is a good idea,
because, right now most of this is about where things are installed,
but, eventually we might have to start actually patching software to
make it work if it is installed on / instead of /usr, and there is no
way to know how much patching we would have to do.

What are your thoughts?

William


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