2 files changed, 90 insertions, 0 deletions
diff --git a/src/system-update-generator/meson.build b/src/system-update-generator/meson.build
new file mode 100644
index 0000000..cc62919
--- /dev/null
+++ b/src/system-update-generator/meson.build
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+
+executables += [
+        generator_template + {
+                'name' : 'systemd-system-update-generator',
+                'sources' : files('system-update-generator.c'),
+        },
+]
diff --git a/src/system-update-generator/system-update-generator.c b/src/system-update-generator/system-update-generator.c
new file mode 100644
index 0000000..a1782d5
--- /dev/null
+++ b/src/system-update-generator/system-update-generator.c
@@ -0,0 +1,82 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <unistd.h>
+
+#include "fs-util.h"
+#include "generator.h"
+#include "initrd-util.h"
+#include "log.h"
+#include "path-util.h"
+#include "proc-cmdline.h"
+#include "special.h"
+#include "string-util.h"
+#include "unit-file.h"
+
+/*
+ * Implements the logic described in systemd.offline-updates(7).
+ */
+
+static const char *arg_dest = NULL;
+
+static int generate_symlink(void) {
+        FOREACH_STRING(p, "/system-update", "/etc/system-update") {
+                if (laccess(p, F_OK) >= 0) {
+                        _cleanup_free_ char *j = NULL;
+
+                        j = path_join(arg_dest, SPECIAL_DEFAULT_TARGET);
+                        if (!j)
+                                return log_oom();
+
+                        if (symlink(SYSTEM_DATA_UNIT_DIR "/system-update.target", j) < 0)
+                                return log_error_errno(errno, "Failed to create symlink %s: %m", j);
+
+                        return 1;
+                }
+
+                if (errno != ENOENT)
+                        log_warning_errno(errno, "Failed to check if %s symlink exists, ignoring: %m", p);
+        }
+
+        return 0;
+}
+
+static int parse_proc_cmdline_item(const char *key, const char *value, void *data) {
+        assert(key);
+
+        /* Check if a run level is specified on the kernel command line. The
+         * command line has higher priority than any on-disk configuration, so
+         * it'll make any symlink we create moot.
+         */
+
+        if (streq(key, "systemd.unit") && !proc_cmdline_value_missing(key, value))
+                log_warning("Offline system update overridden by kernel command line systemd.unit= setting");
+        else if (!value && runlevel_to_target(key))
+                log_warning("Offline system update overridden by runlevel \"%s\" on the kernel command line", key);
+
+        return 0;
+}
+
+static int run(const char *dest, const char *dest_early, const char *dest_late) {
+        int r;
+
+        assert_se(arg_dest = dest_early);
+
+        if (in_initrd()) {
+                log_debug("Skipping generator, running in the initrd.");
+                return EXIT_SUCCESS;
+        }
+
+        r = generate_symlink();
+        if (r <= 0)
+                return r;
+
+        /* We parse the command line only to emit warnings. */
+        r = proc_cmdline_parse(parse_proc_cmdline_item, NULL, 0);
+        if (r < 0)
+                log_warning_errno(r, "Failed to parse kernel command line, ignoring: %m");
+
+        return 0;
+}
+
+DEFINE_MAIN_GENERATOR_FUNCTION(run);