Re: Bug#839046: debootstrap: enable --merged-usr by default

[Guillem Jover <guillem@debian.org>]

On Mon, 2018-02-05 at 22:32:05 +0000, Holger Levsen wrote:
> On Mon, Feb 05, 2018 at 08:19:33PM +0100, Julien Cristau wrote:
> > On Sat, Feb  3, 2018 at 09:16:40 +0100, Marco d'Itri wrote:
> > > On Dec 23, md wrote:
> > > > On Dec 20, Julien Cristau <jcristau@debian.org> wrote:
> > > > > > This change was reverted in 1.0.87 as dpkg-shlibdeps didn't cope
> > > > > > properly with a merged-usr system. Thus reopening this bug report for
> > > > > > that version.
> > > > > > 
> > > > > > The dpkg-shlibdeps bugs has been fixed [1] in the mean time. So it would
> > > > > > be great if this bug report could be re-considered.

> > > > > That'll be after stretch now.

> > > > Stretch was been released long ago: please re-enable --merged-usr in 
> > > > debootstrap.

> > > There has not been any negative feedback, can we move on please?

> > Is there buy-in from the dpkg maintainer?

As I've mentioned in the past, I think the usrmerge filesystem layout
has merit and can solve some issues, and to state it very clearly, I
have no technical issue with it *what*so*ever*. But the same can be
said about the non-usrmerge layout with multiple mount-points, which
while not general anymore in Debian, can still be used perfectly fine
on controlled subsets of packages and custom built kernels w/o reliance
on an initramfs.

What I still find to be terrible is the way it's been tried to be
deployed in Debian, via the usrmerge package, which does not support
reverting the change (#848626), for which there's (AFAIK) no way to
select not using this irreversible hack from d-i, which breaks
dpkg-query --search (at least #848622 and #858331). This seems like
a nice PoV for people to play with it, in the same way local admins
can use, to some extent, symlinks to redirect subtrees to other mount
points, but I don't see how this can be seen as a production-ready
solution shipped by default, TBH.

In any case, I looked the other day into implementing the
--map-pathname option for dpkg-query, and I've got most of the code
ready. The problem is that this requires adding support for config
files and config fragments to dpkg-query, which has the additional
problem of making it possible to mess with the --showformat option
and breaking the expectations from maintscripts, for example. The
other problem is with the search behavior changing depending on the
packages providing those mappings being installed (because dpkg would
certainly not provide them).


So I'll eventually try to find a solution for the dpkg-query issue,
because it's a long-standing paper-cut in dpkg for local admins. But
I'd not be very amused if this hack is enabled by default again and
suddenly RC bugs start popping up in dpkg again, and people start
pressuring with RCness to get those fixed again because well, it's
obviously breaking people's systems…


Thanks,
Guillem