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Re: usrmerge -- plan B?




On Tue, Nov 27, 2018 at 12:57:38PM +0000, Ian Jackson wrote:
> > In the case of unmerged /usr, the only benefits I'm aware of for the more
> > complex case (unmerged /usr) are circular: existing Debian installations
> > have it, so switching to merged /usr is a change;

> I think this is true for Debian itself now that we have bitten the
> bullet of requiring /usr to be mounted along with /, early during
> boot.  (For the record I think that was a good decision.)

> Unmerged /usr could have continuing benefits for Debian derivatives
> who have avoided requiring early mounting of /usr.  IDK whether such
> derivatives exist.  They could do, if they support a narrower range of
> approaches to storage access than Debian proper.  If such derivatives
> exist then Debian adopting merged /usr would be likely to cause
> problems for them, as we would introduce changes in Debian which would
> be bugs in those derivatives.  I don't know how serious a problem that
> would be.

Support for such a configuration is actively bitrotting as we speak. 
Library dependencies of /bin and /sbin are no longer isolated in /lib; udev
will not reliably set up all devices without access to programs under /usr. 
Even if some derivative based on a recent Debian release has managed to keep
usr-on-separate-partition-without-initramfs working for their purposes, this
is not sensibly maintainable over the longer term, and the existence of such
a derivative should carry very little weight with Debian when deciding
whether to merge /usr.

Example: even *without* merged /usr, an entirely sensible course of action
for any maintainer of a Debian library package is to undo all special casing
of /lib vs. /usr/lib in their debian/rules (.so -dev symlinks vs. runtime
libraries, etc) and ship everything in /usr/lib, because the maintainer can
rely on /usr/lib always being available.

> I think it would be good to hear from any derivatives in this
> position.  We should probably ask them more formally than by having a
> horrible flamewar on -devel: ie, in a way that invites the expression
> of concerns and which reassures people that they will not be flamed or
> dismissed.  That would satisfy what I see as our social duty to
> consult our downstreams.  And if we did that and didn't get replies,
> that might give us confidence that such derivatives don't exist.  So
> we could go ahead with a clear conscience.

I don't agree that there's a social duty to consult downstreams that have
made self-evidently poor engineering decisions, before making a change that
will inconvenience them solely as a result of those same poor decisions.

I don't mean that I'm unsympathetic to downstreams in that situation, or
that I wouldn't want to help them; only that their plight /should not/ be an
obstacle to Debian doing the right thing.

-- 
Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                   https://www.debian.org/
slangasek@xxxxxxxxxx                                     vorlon@xxxxxxxxxx

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