dnfdaemon: Add system_upgrade() method to Rpm interface

The method fills the goal to perform upgrade of the distribution to the
new release.

dnf5daemon-server/dbus/interfaces/org.rpm.dnf.v0.rpm.Rpm.xml

@@ -212,6 +212,24 @@ along with libdnf.  If not, see <https://www.gnu.org/licenses/>.
         <arg name="options" type="a{sv}" direction="in" />
     </method>
 
+    <!--
+        system_upgrade:
+        @options: an array of key/value pairs to modify system_upgrade behavior
+
+        Prepare a transaction for upgrade to the new distribution release. The prepared transaction should be executed during reboot (see `offline` option of the `do_transaction` method of the `Goal` interface).
+        The method relies on the `releasever` option being correctly set to the new distribution release during the `open_session()` call.
+
+        Following @options are supported:
+
+            - mode: string (one of "distrosync", "upgrade", default is "distrosync")
+                By default the system_upgrade behaves like `dnf distro-sync`, always installing packages from the new release, even if they are older than the currently installed version. If set to "upgrade", packages from the new release are not installed if they are older than what is currently installed (behave like `dnf upgrade`).
+
+        Unknown options are ignored.
+    -->
+    <method name="system_upgrade">
+        <arg name="options" type="a{sv}" direction="in" />
+    </method>
+
     <!--
         transaction_elem_progress:
         @session_object_path: object path of the dnf5daemon session

dnf5daemon-server/services/rpm/rpm.cpp

@@ -113,6 +113,16 @@ void Rpm::dbus_register() {
         [this](sdbus::MethodCall call) -> void {
             session.get_threads_manager().handle_method(*this, &Rpm::remove, call, session.session_locale);
         });
+    dbus_object->registerMethod(
+        dnfdaemon::INTERFACE_RPM,
+        "system_upgrade",
+        "a{sv}",
+        {"options"},
+        "",
+        {},
+        [this](sdbus::MethodCall call) -> void {
+            session.get_threads_manager().handle_method(*this, &Rpm::system_upgrade, call, session.session_locale);
+        });
 
     dbus_object->registerSignal(
         dnfdaemon::INTERFACE_RPM, dnfdaemon::SIGNAL_TRANSACTION_BEFORE_BEGIN, "ot", {"session_object_path", "total"});
@@ -623,3 +633,46 @@ sdbus::MethodReply Rpm::remove(sdbus::MethodCall & call) {
     auto reply = call.createReply();
     return reply;
 }
+
+sdbus::MethodReply Rpm::system_upgrade(sdbus::MethodCall & call) {
+    if (!session.check_authorization(dnfdaemon::POLKIT_EXECUTE_RPM_TRANSACTION, call.getSender())) {
+        throw std::runtime_error("Not authorized");
+    }
+    auto base = session.get_base();
+
+    // read options from dbus call
+    dnfdaemon::KeyValueMap options;
+    call >> options;
+
+    // check that releasever is different than the detected one
+    auto target_releasever = base->get_vars()->get_value("releasever");
+    const std::filesystem::path installroot{base->get_config().get_installroot_option().get_value()};
+    const auto & detected_releasever = libdnf5::Vars::detect_release(base->get_weak_ptr(), installroot);
+    if (detected_releasever != nullptr) {
+        if (target_releasever == *detected_releasever) {
+            throw sdbus::Error(
+                dnfdaemon::ERROR, fmt::format("Need a 'releasever' different than the current system version."));
+        }
+    }
+
+    // get the upgrade mode
+    std::string upgrade_mode = dnfdaemon::key_value_map_get<std::string>(options, "mode", "distrosync");
+
+    // fill the goal
+    auto & goal = session.get_goal();
+    libdnf5::GoalJobSettings settings;
+    if (upgrade_mode == "upgrade") {
+        goal.add_rpm_upgrade(settings);
+    } else if (upgrade_mode == "distrosync") {
+        goal.add_rpm_distro_sync(settings);
+    } else {
+        throw sdbus::Error(
+            dnfdaemon::ERROR,
+            fmt::format(
+                "Unsupported system-upgrade mode \"{}\". Only \"distrosync\" and \"upgrade\" modes are supported.",
+                upgrade_mode));
+    }
+
+    auto reply = call.createReply();
+    return reply;
+}

dnf5daemon-server/services/rpm/rpm.hpp

@@ -43,6 +43,7 @@ class Rpm : public IDbusSessionService {
     sdbus::MethodReply distro_sync(sdbus::MethodCall & call);
     sdbus::MethodReply downgrade(sdbus::MethodCall & call);
     sdbus::MethodReply reinstall(sdbus::MethodCall & call);
+    sdbus::MethodReply system_upgrade(sdbus::MethodCall & call);
 
     void list_fd(sdbus::MethodCall & call, const std::string & transfer_id);
 };