Configure the amount of kernels to keep

This commit introduces the following configuration for keeping a
configurable amount of kernels: APT::NeverAutoRemove::KernelCount

The logic dictates that the running kernel and the latest kernel are not
autoremoved. In case the running kernel is the latest kernel, the
previous kernel is kept. Any count lower than two is therefore
disregarded. This is in line with the previous behavior.

The default is therefore similar to:
APT::NeverAutoRemove::KernelCount 2;

This will be ignored and we will still keep two:
APT::NeverAutoRemove::KernelCount 1;

This will keep 3 kernels (including the runnig, and most recent)
APT::NeverAutoRemove::KernelCount 3;

Signed-off-by: Wesley Schwengle <wesleys@opperschaap.net>

2 files changed, 21 insertions, 13 deletions

diff --git a/apt-pkg/algorithms.cc b/apt-pkg/algorithms.cc
index 3d4096a94..0d9b50e2c 100644
--- a/apt-pkg/algorithms.cc
+++ b/apt-pkg/algorithms.cc
@@ -1554,30 +1554,37 @@ std::string GetProtectedKernelsRegex(pkgCache *cache, bool ReturnRemove)
    if (version2unames.size() == 0)
       return "";
 
-   auto latest = version2unames.rbegin();
-   auto previous = latest;
-   ++previous;
-
+   auto versions = version2unames.rbegin();
    std::set<std::string> keep;
 
+   auto keepKernels = (unsigned long)_config->FindI("APT::NeverAutoRemove::KernelCount", 2);
+   if (keepKernels < 2)
+      keepKernels = 2;
+
+   if (Debug)
+      std::clog << "Amount of kernels to keep " << keepKernels << std::endl;
+
    if (not bootedVersion.empty())
    {
       if (Debug)
 	 std::clog << "Keeping booted kernel " << bootedVersion << std::endl;
       keep.insert(bootedVersion);
    }
-   if (latest != version2unames.rend())
-   {
-      if (Debug)
-	 std::clog << "Keeping latest kernel " << latest->first << std::endl;
-      keep.insert(latest->first);
-   }
-   if (keep.size() < 2 && previous != version2unames.rend())
+
+   while (keep.size() < keepKernels && versions != version2unames.rend())
    {
+      auto v = versions->first;
+      if (v == bootedVersion)
+      {
+	 versions++;
+	 continue;
+      }
       if (Debug)
-	 std::clog << "Keeping previous kernel " << previous->first << std::endl;
-      keep.insert(previous->first);
+	 std::clog << "Keeping previous kernel " << v << std::endl;
+      keep.insert(v);
+      versions++;
    }
+
    // Escape special characters '.' and '+' in version strings so we can build a regular expression
    auto escapeSpecial = [](std::string input) -> std::string {
       for (size_t pos = 0; (pos = input.find_first_of(".+", pos)) != input.npos; pos += 2) {
diff --git a/doc/examples/configure-index b/doc/examples/configure-index
index 0d4dd31a5..f37b7696c 100644
--- a/doc/examples/configure-index
+++ b/doc/examples/configure-index
@@ -55,6 +55,7 @@ APT
   Build-Profiles "<STRING_OR_LIST>";
 
   NeverAutoRemove "<LIST>";  // list of package name regexes
+  NeverAutoRemove::KernelCount "<INT>"; // Keep the configured amount of kernels
   LastInstalledKernel "<STRING>"; // last installed kernel version
   VersionedKernelPackages "<LIST>"; // regular expressions to be protected from autoremoval (kernel uname will be appended)
   Protect-Kernels "<BOOL>"; // whether to protect installed kernels against autoremoval (default: true)