sd-daemon: introduce sd_pid_notify() and sd_pid_notifyf()

sd_pid_notify() operates like sd_notify(), however operates on a
different PID (for example the parent PID of a process).

Make use of this in systemd-notify, so that message are sent from the
PID specified with --pid= rather than the usually shortlived PID of
systemd-notify itself.

This should increase the likelyhood that PID 1 can identify the cgroup
that the notification message was sent from properly.

src/notify/notify.c

@@ -147,25 +147,25 @@ static int parse_argv(int argc, char *argv[]) {
 }
 
 int main(int argc, char* argv[]) {
-        char* our_env[4], **final_env = NULL;
+        _cleanup_free_ char *status = NULL, *cpid = NULL, *n = NULL;
+        _cleanup_strv_free_ char **final_env = NULL;
+        char* our_env[4];
         unsigned i = 0;
-        char *status = NULL, *cpid = NULL, *n = NULL;
-        int r, retval = EXIT_FAILURE;
+        int r;
 
         log_parse_environment();
         log_open();
 
         r = parse_argv(argc, argv);
-        if (r <= 0) {
-                retval = r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
+        if (r <= 0)
                 goto finish;
-        }
 
         if (arg_booted)
                 return sd_booted() <= 0;
 
         if (arg_readahead) {
-                if ((r = sd_readahead(arg_readahead)) < 0) {
+                r = sd_readahead(arg_readahead);
+                if (r < 0) {
                         log_error("Failed to issue read-ahead control command: %s", strerror(-r));
                         goto finish;
                 }
@@ -175,8 +175,9 @@ int main(int argc, char* argv[]) {
                 our_env[i++] = (char*) "READY=1";
 
         if (arg_status) {
-                if (!(status = strappend("STATUS=", arg_status))) {
-                        log_error("Failed to allocate STATUS string.");
+                status = strappend("STATUS=", arg_status);
+                if (!status) {
+                        r = log_oom();
                         goto finish;
                 }
 
@@ -185,7 +186,7 @@ int main(int argc, char* argv[]) {
 
         if (arg_pid > 0) {
                 if (asprintf(&cpid, "MAINPID="PID_FMT, arg_pid) < 0) {
-                        log_error("Failed to allocate MAINPID string.");
+                        r = log_oom();
                         goto finish;
                 }
 
@@ -194,34 +195,32 @@ int main(int argc, char* argv[]) {
 
         our_env[i++] = NULL;
 
-        if (!(final_env = strv_env_merge(2, our_env, argv + optind))) {
-                log_error("Failed to merge string sets.");
+        final_env = strv_env_merge(2, our_env, argv + optind);
+        if (!final_env) {
+                r = log_oom();
                 goto finish;
         }
 
         if (strv_length(final_env) <= 0) {
-                retval = EXIT_SUCCESS;
+                r = 0;
                 goto finish;
         }
 
-        if (!(n = strv_join(final_env, "\n"))) {
-                log_error("Failed to concatenate strings.");
+        n = strv_join(final_env, "\n");
+        if (!n) {
+                r = log_oom();
                 goto finish;
         }
 
-        if ((r = sd_notify(false, n)) < 0) {
+        r = sd_pid_notify(arg_pid, false, n);
+        if (r < 0) {
                 log_error("Failed to notify init system: %s", strerror(-r));
                 goto finish;
         }
 
-        retval = r <= 0 ? EXIT_FAILURE : EXIT_SUCCESS;
+        if (r == 0)
+                r = -ENOTSUP;
 
 finish:
-        free(status);
-        free(cpid);
-        free(n);
-
-        strv_free(final_env);
-
-        return retval;
+        return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
 }