Prevent shutdown while running dpkg

As long as we are running dpkg, keep an inhibitor that
blocks us from shutting down.

LP: #1820886
(cherry picked from commit 96aef11a5cf400377a52f7e93e70944b17e249d1)
(cherry picked from commit 8ea79afcadead5a5b7d94bf8623cb833859f6d80)

9 files changed, 103 insertions, 0 deletions

diff --git a/CMake/FindSystemd.cmake b/CMake/FindSystemd.cmake
new file mode 100644
index 000000000..1c7a7debf
--- /dev/null
+++ b/CMake/FindSystemd.cmake
@@ -0,0 +1,24 @@
+# - Try to find SYSTEMD
+# Once done, this will define
+#
+#  SYSTEMD_FOUND - system has SYSTEMD
+#  SYSTEMD_INCLUDE_DIRS - the SYSTEMD include directories
+#  SYSTEMD_LIBRARIES - the SYSTEMD library
+find_package(PkgConfig)
+
+pkg_check_modules(SYSTEMD_PKGCONF libsystemd)
+
+find_path(SYSTEMD_INCLUDE_DIRS
+  NAMES systemd/sd-bus.h
+  PATHS ${SYSTEMD_PKGCONF_INCLUDE_DIRS}
+)
+
+find_library(SYSTEMD_LIBRARIES
+  NAMES systemd
+  PATHS ${SYSTEMD_PKGCONF_LIBRARY_DIRS}
+)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(Systemd DEFAULT_MSG SYSTEMD_INCLUDE_DIRS SYSTEMD_LIBRARIES)
+
+mark_as_advanced(SYSTEMD_INCLUDE_DIRS SYSTEMD_LIBRARIES)
diff --git a/CMake/config.h.in b/CMake/config.h.in
index bd0da8649..22be6998e 100644
--- a/CMake/config.h.in
+++ b/CMake/config.h.in
@@ -20,6 +20,9 @@
 /* Define if we have the zstd library for zst */
 #cmakedefine HAVE_ZSTD
 
+/* Define if we have the systemd library */
+#cmakedefine HAVE_SYSTEMD
+
 /* Define if we have the udev library */
 #cmakedefine HAVE_UDEV
 
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0481f4ee8..b45692517 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -114,6 +114,11 @@ if (UDEV_FOUND)
   set(HAVE_UDEV 1)
 endif()
 
+find_package(Systemd)
+if (SYSTEMD_FOUND)
+  set(HAVE_SYSTEMD 1)
+endif()
+
 find_package(Seccomp)
 if (SECCOMP_FOUND)
   set(HAVE_SECCOMP 1)
diff --git a/apt-pkg/CMakeLists.txt b/apt-pkg/CMakeLists.txt
index 64709ce34..ce73c6a34 100644
--- a/apt-pkg/CMakeLists.txt
+++ b/apt-pkg/CMakeLists.txt
@@ -46,6 +46,7 @@ target_include_directories(apt-pkg
                                    ${LZ4_INCLUDE_DIRS}
                                    $<$<BOOL:${ZSTD_FOUND}>:${ZSTD_INCLUDE_DIRS}>
                                    $<$<BOOL:${UDEV_FOUND}>:${UDEV_INCLUDE_DIRS}>
+                                   $<$<BOOL:${SYSTEMD_FOUND}>:${SYSTEMD_INCLUDE_DIRS}>
                                    ${ICONV_INCLUDE_DIRS}
 )
 
@@ -58,6 +59,7 @@ target_link_libraries(apt-pkg
                              ${LZ4_LIBRARIES}
                              $<$<BOOL:${ZSTD_FOUND}>:${ZSTD_LIBRARIES}>
                              $<$<BOOL:${UDEV_FOUND}>:${UDEV_LIBRARIES}>
+                             $<$<BOOL:${SYSTEMD_FOUND}>:${SYSTEMD_LIBRARIES}>
                              ${ICONV_LIBRARIES}
 )
 set_target_properties(apt-pkg PROPERTIES VERSION ${MAJOR}.${MINOR})
diff --git a/apt-pkg/contrib/fileutl.cc b/apt-pkg/contrib/fileutl.cc
index eab05de4f..b38186b3d 100644
--- a/apt-pkg/contrib/fileutl.cc
+++ b/apt-pkg/contrib/fileutl.cc
@@ -71,6 +71,9 @@
 #ifdef HAVE_ZSTD
 #include <zstd.h>
 #endif
+#ifdef HAVE_SYSTEMD
+#include <systemd/sd-bus.h>
+#endif
 #include <endian.h>
 #include <stdint.h>
 
@@ -3387,3 +3390,48 @@ bool OpenConfigurationFileFd(std::string const &File, FileFd &Fd) /*{{{*/
    return true;
 }
 									/*}}}*/
+int Inhibit(const char *what, const char *who, const char *why, const char *mode) /*{{{*/
+{
+#ifdef HAVE_SYSTEMD
+   sd_bus_error error = SD_BUS_ERROR_NULL;
+   sd_bus_message *m = NULL;
+   sd_bus *bus = NULL;
+   int fd;
+   int r;
+
+   r = sd_bus_open_system(&bus);
+   if (r < 0)
+      goto out;
+
+   r = sd_bus_call_method(bus,
+			  "org.freedesktop.login1",
+			  "/org/freedesktop/login1",
+			  "org.freedesktop.login1.Manager",
+			  "Inhibit",
+			  &error,
+			  &m,
+			  "ssss",
+			  what,
+			  who,
+			  why,
+			  mode);
+   if (r < 0)
+      goto out;
+
+   r = sd_bus_message_read(m, "h", &fd);
+   if (r < 0)
+      goto out;
+
+   // We received a file descriptor, return it - systemd will close the read fd
+   // on free, so let's duplicate it here.
+   r = dup(fd);
+out:
+   sd_bus_error_free(&error);
+   sd_bus_message_unref(m);
+   sd_bus_unref(bus);
+   return r;
+#else
+   return -ENOTSUP;
+#endif
+}
+									/*}}}*/
diff --git a/apt-pkg/contrib/fileutl.h b/apt-pkg/contrib/fileutl.h
index 6249b7c16..35cd8139a 100644
--- a/apt-pkg/contrib/fileutl.h
+++ b/apt-pkg/contrib/fileutl.h
@@ -294,4 +294,6 @@ bool Popen(const char* Args[], FileFd &Fd, pid_t &Child, FileFd::OpenMode Mode);
 
 APT_HIDDEN bool OpenConfigurationFileFd(std::string const &File, FileFd &Fd);
 
+APT_HIDDEN int Inhibit(const char *what, const char *who, const char *why, const char *mode);
+
 #endif
diff --git a/apt-pkg/deb/dpkgpm.cc b/apt-pkg/deb/dpkgpm.cc
index c8e55fe14..2700bef7b 100644
--- a/apt-pkg/deb/dpkgpm.cc
+++ b/apt-pkg/deb/dpkgpm.cc
@@ -1463,6 +1463,21 @@ bool pkgDPkgPM::ExpandPendingCalls(std::vector<Item> &List, pkgDepCache &Cache)
 }
 bool pkgDPkgPM::Go(APT::Progress::PackageManager *progress)
 {
+   struct Inhibitor
+   {
+      int Fd = -1;
+      Inhibitor()
+      {
+	 if (_config->FindB("DPkg::Inhibit-Shutdown", true))
+	    Fd = Inhibit("shutdown", "APT", "APT is installing or removing packages", "block");
+      }
+      ~Inhibitor()
+      {
+	 if (Fd > 0)
+	    close(Fd);
+      }
+   } inhibitor;
+
    // explicitly remove&configure everything for hookscripts and progress building
    // we need them only temporarily through, so keep the length and erase afterwards
    decltype(List)::const_iterator::difference_type explicitIdx =
diff --git a/debian/control b/debian/control
index 333150ff8..be0706439 100644
--- a/debian/control
+++ b/debian/control
@@ -22,6 +22,7 @@ Build-Depends: cmake (>= 3.4),
                liblz4-dev (>= 0.0~r126),
                liblzma-dev,
                libseccomp-dev [amd64 arm64 armel armhf i386 mips mips64el mipsel ppc64el s390x hppa powerpc powerpcspe ppc64 x32],
+               libsystemd-dev [linux-any],
                libudev-dev [linux-any],
                libzstd-dev (>= 1.0),
                pkg-config,
diff --git a/doc/examples/configure-index b/doc/examples/configure-index
index df91d7738..bdfb1ad5e 100644
--- a/doc/examples/configure-index
+++ b/doc/examples/configure-index
@@ -498,6 +498,9 @@ DPkg
       progress-bg "<STRING>";
       progress-bar "<BOOL>";
    };
+
+   // Set a shutdown block inhibitor on systemd systems while running dpkg
+   Inhibit-Shutdown "<BOOL>";
 }
 
 /* Options you can set to see some debugging text They correspond to names