Add support for Phased-Update-Percentage

This adds support for Phased-Update-Percentage by pinning
upgrades that are not to be installed down to 1.

The output of policy has been changed to add the level of
phasing, and documentation has been improved to document
how phased updates work.

The patch detects if it is running in a chroot, and if so, always
includes phased updates, restoring classic apt behavior to avoid
behavioral changes on buildd chroots.

Various options are added to control this all:

* APT::Get::{Always,Never}-Include-Phased-Updates and their legacy
  update-manager equivalents to always or never include phased updates
* APT::Machine-ID can be set to a UUID string to have all machines in a
  fleet phase the same
* Dir::Etc::Machine-ID is weird in that it's default is sort of like
  ../machine-id, but not really, as ../machine-id would look up
  $PWD/../machine-id and not relative to Dir::Etc; but it allows you to
  override the path to machine-id (as opposed to the value)
* Dir::Bin::ischroot is the path to the ischroot(1) binary which is used
  to detect whether we are running in a chroot.

1 files changed, 7 insertions, 0 deletions

diff --git a/apt-pkg/deb/deblistparser.cc b/apt-pkg/deb/deblistparser.cc
index 95f6f6fc8..b5c9c066e 100644
--- a/apt-pkg/deb/deblistparser.cc
+++ b/apt-pkg/deb/deblistparser.cc
@@ -338,6 +338,13 @@ bool debListParser::UsePackage(pkgCache::PkgIterator &Pkg,
    else if (std::find(forceImportant.begin(), forceImportant.end(), Pkg.Name()) != forceImportant.end())
       Pkg->Flags |= pkgCache::Flag::Important;
 
+   auto phased = Section.FindULL(pkgTagSection::Key::Phased_Update_Percentage, 100);
+   if (phased != 100)
+   {
+      if (not Ver.PhasedUpdatePercentage(phased))
+	 _error->Warning("Ignoring invalid Phased-Update-Percentage value");
+   }
+
    if (ParseStatus(Pkg,Ver) == false)
       return false;
    return true;