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Re: usrmerge -- plan B?

On Sun, 2018-12-02 at 13:40:05 +0200, Niko Tyni wrote:
> On Fri, Nov 23, 2018 at 04:32:17PM +0100, Guillem Jover wrote:
> > Please, if we decide we want to do merged /usr, let's do it properly.
> I'm toying with the idea of creating a merged-usr package indicating
> 'this system has merged /usr'. It could either fail to install with an
> informational message on unmerged-usr systems, or if we're brave enough,
> interactively or automatically convert the system (possibly utilizing
> the usrmerge package.)
> Then debhelper (or even dpkg-dev) could probe whether the build system
> has merged /usr, and automatically add dependencies on merged-usr to
> resulting binary packages, The dependency injection could be on either
> an opt-out or an opt-in basis.
> The opt-out way would be the more safe and conservative approach,
> assuming everything built on merged /usr is broken on non-merged /usr
> unless the maintainer indicates otherwise.
> On the contrary, the opt-in approach would require that all problematic
> packages (those that will not function fine when built on merged /usr
> systems but installed on non-merged /usr ones) be identified and tagged
> as needing this dependency. This obviously has a chance of missing
> some of the issues.
> Whether opt-out or opt-in, the transition in Debian could then be
> controlled by monitoring dependencies on merged-usr, possibly playing
> whack-a-mole rebuilding things that have gained this dependency in
> maintainer uploads, or letting the gates open at some point and allowing
> even core packages to gain this dependency (effectively forcing /usr
> merge on all systems.)
> All this would make the issues explicit and reflected in the package
> dependency metadata, which seems to me like at least a step forward.

IMO this would make it even worse than what it is right now. And I
think it still keeps missing the point. :/

The current merged-/usr deployment (via usrmerge or the bootstrapping
symlink generation before unpack) is a major hack, and bypasses the
dpkg understanding of the filesystem, it breaks dpkg-query, and while
we could workaround the breakage there, it's still the wrong way to go
around this.

The main reasons I'm reading to justify it are, "because it's faster,
and requires less effort", I mean, seriously… and as a "bonus" we now
have the ctte involved again. Great setup really.