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Re: usrmerge -- plan B?

Marco d'Itri <md@Linux.IT> writes:
> On Nov 21, Russ Allbery <rra@debian.org> wrote:

>> I think there are some arguments to be made for just force-merging and
>> moving on, but they're mostly "tidiness" arguments (letting everyone

> No, they are not that at all. I have never argued about "tidiness", nor
> did anybody else that is working to support merged-/usr.  A merged-/usr
> is an enabler for new features, like stateless systems, clones,
> appliances and better containers.  Simon McVittie today was patient
> enough to explain some of them.

I read all of Simon's message, which was excellent and which I greatly
appreciate.  The arguments he listed there are, however, the arguments I
was classifying as "tidiness" arguments.

We shouldn't get caught up on terminology, since whether or not my
adjective is correct isn't really the point.  The point is that every use
case he describes is possible without usrmerge.  It's just more
complicated because it requires manipulating multiple paths instead of
one, which requires a bit more ingenuity and fragility (via symlink
redirections and the like) to make atomic.

I completely understand why merged /usr makes it easier, and removes a lot
of avoidable bugs.  But it is not a *requirement* for doing any of the
things that he spells out in that message.  There is still a tradeoff

>> strategy of (for example) moving each binary out of /bin manually, but

> As I explained, this cannot really work.

Of course it can work.  It will just take forever and produce a bunch of
minor bugs along the way and won't be something you'll be able to wait for
before tackling other goals.

In reality, it might well mean just giving up on merging entirely because
people won't be willing to sustain the effort over that length of time.

Personally, I consider separate /bin and /usr/bin to be a historic
artifact whose remaining useful properties have become obsolete or been
replaced with other, better techniques (such as mounting /usr in
initramfs), and we'd all be better off following Red Hat and Arch, dealing
with the pain of merging every system, and then saving ourselves the time
and energy we spend on this separation.  It definitely makes some system
design patterns simpler.  I also agree that this isn't a diversity
question; so far as I know, there aren't any remaining viable use cases
for split /bin and /usr/bin that work in Debian today or have any hope of
working in a Debian of the future.  /bin is already useless without /usr
mounted, and is basically certain to remain so.  The remaining argument is
just that the transition is difficult and may not be worth the effort.

But it's not just my opinion that matters.  I think we need to decide this
somehow as a project, whether via the TC or via GR or something, because
there's a real disagreement here over whether we can or should
force-upgrade all Debian systems and I don't believe doing something short
of that is going to be supportable.

Russ Allbery (rra@debian.org)               <http://www.eyrie.org/~eagle/>

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