** Branch linked: lp:ubuntu/libxext

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https://bugs.launchpad.net/bugs/733501

Title:
  FFe: transitioning libraries to multiarch paths

Status in Ubuntu:
  Confirmed

Bug description:
  (Filed without a package as there are a large number of packages
  affected)

  With the next upload of dpkg, all the pieces will be in place to begin
  migrating our library packages to use the multiarch library paths for
  <https://blueprints.launchpad.net/ubuntu/+spec/packageselection-
  foundations-n-multiarch-support>.  Individually the changes are low
  risk, the design has been agreed for over a year and I have
  aggressively tested in my ppa, but given the large number of affected
  packages and that this is ultimately a new feature rather than a
  bugfix, I think a FFe request is in order.

  The overall plan is:
   - push a new dpkg version that implements support for the final library paths
   - bootstrap gcc and eglibc to use the paths (requires two gcc uploads with 
an intervening eglibc upload)
   - push debhelper and pkg-config patches to support multiarch
   - write up documentation for how to transition libraries, and announce this 
on ubuntu-devel
   - convert the desktop library stack, one library at a time

  The transition documentation is not written yet, because it partially
  depends on the finer details of the patch accepted by debhelper
  upstream.

  My target for this cycle, which I believe is a realistic one, is to
  get flashplugin-installer:i386 co-installable with an amd64 desktop
  stack.  This involves converting just over 100 library packages to the
  multiarch paths (highly parallelizable once we get going).  Is this
  acceptable to the release team, and when do we need to be done with
  these changes for natty? before beta?

  Risks I'm aware of with this transition:
   - there are a handful of i386 packages in the archive that will be broken by 
the transition, because they install to the provisional library paths rather 
than the final ones we're using.  These packages are lib32ffi-dev, libffi-dev, 
libhwloc-dev, liblouis-dev and liblouisxml-dev; they'll need to be fixed soon 
after we upload the new gcc.
   - any library that loads architecture-dependent plugins / modules will need 
additional care to ensure that the system is never left in a broken 
halfway-transitioned state.  For example, I have a patch to pam to prepend a 
multiarch module path to the standard /lib/security path; whereas for glib I 
only have it patched to look in the new gio modules path but *not* the old one, 
resulting in a long list of Breaks: in my ppa package that need to be sorted 
before release (preferably the same way pam solves it).
   - ia32-libs will be broken in various ways by this change, because the 
libraries it rebundles will all come installed in the new multiarch paths and 
ia32-libs will need to adapt.  (Debian policy 9.1.1 does not permit ia32-libs 
to install its contents to the multiarch paths; ia32-libs needs to be fixed up 
to make sure it only installs to /usr/lib32 instead to avoid file conflicts.)  
But even after this fix-up, there may be some regressions in functionality due 
to the changes in module paths mentioned in the previous point; this appears to 
affect glib and gtk in particular, for which ia32-libs ships symlinks under 
/usr/lib.
   - this is very much a one-way transition.  Once we start down this path in 
earnest, it will be infeasible to roll it back for natty.
   - there has been no significant testing of multiarch enablement with package 
manager frontends such as synaptic, software-center, and aptitude, so it may 
not actually be feasible for users to turn on multiarch on the desktop for 
natty if they're using one of these frontends.

  Do I have the release team's blessing to proceed?

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