start: add shmount setup on container start

src/lxc/start.c

@@ -1529,6 +1529,70 @@ static inline int do_share_ns(void *arg)
 	return 0;
 }
 
+static int lxc_setup_shmount(struct lxc_conf *conf) {
+	size_t len_cont;
+	char *full_cont_path;
+	int ret = -1;
+
+	/* Construct the shmount path under the container root */
+	/* +1 for slash */
+	len_cont = strlen(conf->rootfs.mount) + 1 + strlen(conf->lxc_shmount.path_cont);
+	/* +1 for the terminating '\0' */
+	full_cont_path = malloc(len_cont + 1);
+	if(!full_cont_path) {
+		SYSERROR("Not enough memory");
+		return -ENOMEM;
+	}
+	ret = snprintf(full_cont_path, len_cont + 1, "%s/%s", conf->rootfs.mount, conf->lxc_shmount.path_cont);
+	if (ret < 0 || ret >= len_cont + 1) {
+		SYSERROR("Failed to create filename");
+		free(full_cont_path);
+		return -1;
+	}
+
+	/* Check if shmount point is already set up */
+	if (is_shared_mountpoint(conf->lxc_shmount.path_host)) {
+		INFO("Path \"%s\" is already MS_SHARED. Reusing", conf->lxc_shmount.path_host);
+		free(full_cont_path);
+		return 0;
+	}
+
+	/* Create host and cont mount paths */
+	ret = mkdir_p(conf->lxc_shmount.path_host, 0711);
+	if (ret < 0 && errno != EEXIST) {
+		SYSERROR("Failed to create directory \"%s\"", conf->lxc_shmount.path_host);
+		free(full_cont_path);
+		return ret;
+	}
+
+	ret = mkdir_p(full_cont_path, 0711);
+	if (ret < 0 && errno != EEXIST) {
+		SYSERROR("Failed to create directory \"%s\"", full_cont_path);
+		free(full_cont_path);
+		return ret;
+	}
+
+	/* Prepare host mountpoint */
+	ret = mount("tmpfs", conf->lxc_shmount.path_host, "tmpfs",
+				0, "size=100k,mode=0711");
+	if (ret < 0) {
+		SYSERROR("Failed to mount \"%s\"", conf->lxc_shmount.path_host);
+		free(full_cont_path);
+		return ret;
+	}
+	ret = mount(conf->lxc_shmount.path_host, conf->lxc_shmount.path_host, "none",
+				MS_REC | MS_SHARED, "");
+	if (ret < 0) {
+		SYSERROR("Failed to make shared \"%s\"", conf->lxc_shmount.path_host);
+		free(full_cont_path);
+		return ret;
+	}
+
+	INFO("Made shared mount point \"%s\"", conf->lxc_shmount.path_host);
+	free(full_cont_path);
+	return 0;
+}
+
 /* lxc_spawn() performs crucial setup tasks and clone()s the new process which
  * exec()s the requested container binary.
  * Note that lxc_spawn() runs in the parent namespaces. Any operations performed
@@ -1606,6 +1670,25 @@ static int lxc_spawn(struct lxc_handler *handler)
 		}
 	}
 
+	if (conf->lxc_shmount.path_host && !conf->lxc_shmount.path_cont) {
+			ERROR("Missing the container side path to the shared mount point");
+			lxc_sync_fini(handler);
+			return -1;
+	}
+	if (conf->lxc_shmount.path_host) {
+		ret = lxc_setup_shmount(conf);
+		if (ret < 0) {
+			ERROR("Failed to setup shared mount point");
+			lxc_sync_fini(handler);
+			return -1;
+		}
+	}
+
+	if (!cgroup_init(handler)) {
+		ERROR("Failed initializing cgroup support");
+		goto out_delete_net;
+	}
+
 	if (!cgroup_ops->create(cgroup_ops, handler)) {
 		ERROR("Failed creating cgroups");
 		goto out_delete_net;