From 944baec85a7496c1595242a31f6b1b37530451a5 Mon Sep 17 00:00:00 2001
From: Julian Andres Klode <julian.klode@canonical.com>
Date: Thu, 17 Dec 2020 15:19:53 +0100
Subject: Automatically remove unused kernels on dist-upgrade

Kernels clutter /boot and /boot is small size, so we need to take
extra care to remove kernels when possible.
---
 apt-private/private-install.cc | 12 +++++++++++-
 debian/NEWS                    |  7 +++++++
 doc/examples/configure-index   |  4 +++-
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/apt-private/private-install.cc b/apt-private/private-install.cc
index af6697d7f..b110cbdc3 100644
--- a/apt-private/private-install.cc
+++ b/apt-private/private-install.cc
@@ -406,8 +406,15 @@ bool DoAutomaticRemove(CacheFile &Cache)
 {
    bool Debug = _config->FindB("Debug::pkgAutoRemove",false);
    bool doAutoRemove = _config->FindB("APT::Get::AutomaticRemove", false);
+   bool doAutoRemoveKernels = _config->FindB("APT::Get::AutomaticRemove::Kernels", false);
    bool hideAutoRemove = _config->FindB("APT::Get::HideAutoRemove");
 
+   std::unique_ptr<APT::CacheFilter::Matcher> kernelAutoremovalMatcher;
+   if (doAutoRemoveKernels && !doAutoRemove)
+   {
+      kernelAutoremovalMatcher = APT::KernelAutoRemoveHelper::GetProtectedKernelsFilter(Cache, true);
+   }
+
    pkgDepCache::ActionGroup group(*Cache);
    if(Debug)
       std::cout << "DoAutomaticRemove()" << std::endl;
@@ -436,7 +443,7 @@ bool DoAutomaticRemove(CacheFile &Cache)
 	    if(Debug)
 	       std::cout << "We could delete " <<  APT::PrettyPkg(Cache, Pkg) << std::endl;
 
-	 if (doAutoRemove)
+	 if (doAutoRemove || (kernelAutoremovalMatcher != nullptr && (*kernelAutoremovalMatcher)(Pkg)))
 	 {
 	    if(Pkg.CurrentVer() != 0 &&
 	       Pkg->CurrentState != pkgCache::State::ConfigFiles)
@@ -692,6 +699,9 @@ bool DoCacheManipulationFromCommandLine(CommandLine &CmdL, std::vector<PseudoPkg
 	 OpTextProgress Progress(*_config);
 	 bool const distUpgradeMode = strcmp(CmdL.FileList[0], "dist-upgrade") == 0 || strcmp(CmdL.FileList[0], "full-upgrade") == 0;
 
+	 if (distUpgradeMode)
+	    _config->CndSet("APT::Get::AutomaticRemove::Kernels", "true");
+
 	 bool resolver_fail = false;
 	 if (distUpgradeMode == true || UpgradeMode != APT::Upgrade::ALLOW_EVERYTHING)
 	    resolver_fail = APT::Upgrade::Upgrade(Cache, UpgradeMode, &Progress);
diff --git a/debian/NEWS b/debian/NEWS
index 13fc64182..9d9c963c2 100644
--- a/debian/NEWS
+++ b/debian/NEWS
@@ -1,3 +1,10 @@
+apt (2.1.16) UNRELEASED; urgency=medium
+
+  Automatically remove unused kernels on dist-upgrade. To revert to previous
+  behavior, set APT::Get::AutomaticRemove::Kernels to false.
+
+ -- Julian Andres Klode <jak@debian.org>  Mon, 04 Jan 2021 10:47:14 +0100
+
 apt (1.9.11) experimental; urgency=medium
 
   apt(8) now waits for the lock indefinitely if connected to a tty, or
diff --git a/doc/examples/configure-index b/doc/examples/configure-index
index 571bf2369..15b020198 100644
--- a/doc/examples/configure-index
+++ b/doc/examples/configure-index
@@ -80,7 +80,9 @@ APT
      Remove "<BOOL>";
      AllowUnauthenticated "<BOOL>"; // skip security
 
-     AutomaticRemove "<BOOL>";
+     AutomaticRemove "<BOOL>" {
+        "Kernels" "<BOOL>";     // Allow removing kernels even if not removing other packages (true for dist-upgrade)
+     };
      HideAutoRemove "<STRING_OR_BOOL>"; // yes, no, small
 
      Simulate "<BOOL>";
-- 
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