hibernate-resume-generator: add a generator for instantiating the resume unit.

hibernate-resume-generator understands resume= kernel command line parameter
and instantiates the systemd-resume@.service accordingly if it is passed.

This enables resume from hibernation using device specified on the kernel
command line, and it may be specified either as "/dev/disk/by-foo/bar"
or "FOO=bar", not only "/dev/sdXY" which is understood by the in-kernel
implementation.

So now resume= is brought on par with root= in terms of possible ways to
specify a device.

src/resume-generator/Makefile

@@ -0,0 +1 @@
+../Makefile

src/resume-generator/resume-generator.c

@@ -0,0 +1,95 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2014 Ivan Shapovalov
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <stdio.h>
+#include <errno.h>
+
+#include "log.h"
+#include "util.h"
+#include "special.h"
+#include "mkdir.h"
+#include "unit-name.h"
+
+static const char *arg_dest = "/tmp";
+static char *arg_resume_dev = NULL;
+
+static int parse_proc_cmdline_item(const char *key, const char *value) {
+        if (streq(key, "resume") && value) {
+                free(arg_resume_dev);
+                arg_resume_dev = fstab_node_to_udev_node(value);
+                if (!arg_resume_dev)
+                        return log_oom();
+        }
+
+        return 0;
+}
+
+static int process_resume(void) {
+        _cleanup_free_ char *name = NULL, *lnk = NULL;
+
+        name = unit_name_from_path_instance("systemd-hibernate-resume", arg_resume_dev, ".service");
+        if (!name)
+                return log_oom();
+
+        lnk = strjoin(arg_dest, "/" SPECIAL_SYSINIT_TARGET ".wants/", name, NULL);
+        if (!lnk)
+                return log_oom();
+
+        mkdir_parents_label(lnk, 0755);
+        if (symlink(SYSTEM_DATA_UNIT_PATH "/systemd-hibernate-resume@.service", lnk) < 0) {
+                log_error("Failed to create symlink %s: %m", lnk);
+                return -errno;
+        }
+
+        return 0;
+}
+
+int main(int argc, char *argv[]) {
+        int r = 0;
+
+        if (argc > 1 && argc != 4) {
+                log_error("This program takes three or no arguments.");
+                return EXIT_FAILURE;
+        }
+
+        if (argc > 1)
+                arg_dest = argv[1];
+
+        log_set_target(LOG_TARGET_SAFE);
+        log_parse_environment();
+        log_open();
+
+        umask(0022);
+
+        /* Don't even consider resuming outside of initramfs. */
+        if (!in_initrd())
+                return EXIT_SUCCESS;
+
+        if (parse_proc_cmdline(parse_proc_cmdline_item) < 0)
+                return EXIT_FAILURE;
+
+        if (arg_resume_dev != NULL)
+                r = process_resume();
+
+        free(arg_resume_dev);
+
+        return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
+}