1 files changed, 72 insertions, 0 deletions
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..fc5aaa9
--- /dev/null
+++ b/src/system-update-generator/system-update-generator.c
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <unistd.h>
+
+#include "fs-util.h"
+#include "generator.h"
+#include "log.h"
+#include "proc-cmdline.h"
+#include "special.h"
+#include "string-util.h"
+#include "unit-file.h"
+#include "util.h"
+
+/*
+ * Implements the logic described in systemd.offline-updates(7).
+ */
+
+static const char *arg_dest = NULL;
+
+static int generate_symlink(void) {
+        const char *p = NULL;
+
+        if (laccess("/system-update", F_OK) < 0) {
+                if (errno == ENOENT)
+                        return 0;
+
+                log_error_errno(errno, "Failed to check for system update: %m");
+                return -EINVAL;
+        }
+
+        p = strjoina(arg_dest, "/" SPECIAL_DEFAULT_TARGET);
+        if (symlink(SYSTEM_DATA_UNIT_DIR "/system-update.target", p) < 0)
+                return log_error_errno(errno, "Failed to create symlink %s: %m", p);
+
+        return 1;
+}
+
+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);
+
+        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);