+static int do_switch_root(const char *switch_root) {
+ int r=0;
+ /* Don't try to unmount the old "/", there's no way to do it. */
+ const char *umounts[] = { "/dev", "/proc", "/sys", "/run", NULL };
+ int i;
+ int cfd = -1;
+ struct stat switch_root_stat, sb;
+
+ if (path_equal(switch_root, "/"))
+ return 0;
+
+ if (stat(switch_root, &switch_root_stat) != 0) {
+ r = -errno;
+ log_error("failed to stat directory %s", switch_root);
+ goto fail;
+ }
+
+ for (i = 0; umounts[i] != NULL; i++) {
+ char newmount[PATH_MAX];
+
+ snprintf(newmount, sizeof(newmount), "%s%s", switch_root, umounts[i]);
+
+ if ((stat(newmount, &sb) != 0) || (sb.st_dev != switch_root_stat.st_dev)) {
+ /* mount point seems to be mounted already or stat failed */
+ umount2(umounts[i], MNT_DETACH);
+ continue;
+ }
+
+ if (mount(umounts[i], newmount, NULL, MS_MOVE, NULL) < 0) {
+ log_error("failed to mount moving %s to %s",
+ umounts[i], newmount);
+ log_error("forcing unmount of %s", umounts[i]);
+ umount2(umounts[i], MNT_FORCE);
+ }
+ }
+
+ if (chdir(switch_root)) {
+ r = -errno;
+ log_error("failed to change directory to %s", switch_root);
+ goto fail;
+ }
+
+ cfd = open("/", O_RDONLY);
+
+ if (mount(switch_root, "/", NULL, MS_MOVE, NULL) < 0) {
+ r = -errno;
+ log_error("failed to mount moving %s to /", switch_root);
+ goto fail;
+ }
+
+ if (chroot(".")) {
+ r = -errno;
+ log_error("failed to change root");
+ goto fail;
+ }
+
+ if (cfd >= 0) {
+ rm_rf_children(cfd, false, false);
+ close(cfd);
+ cfd=-1;
+ }
+
+ return 0;
+
+fail:
+ if (cfd >= 0)
+ close(cfd);
+
+ log_error("Failed to switch root, ignoring: %s", strerror(-r));
+
+ return r;
+}
+