lxc-start: Add command to retrieve the clone flags used to start the container.

Add the LXC_COMMAND_CLONE_FLAGS that retrieves the flags passed to clone(2)
when the container was started. This allows external programs to determine
which namespaces the container was unshared from.

Signed-off-by: Christian Seiler <christian@iwakd.de>
Cc: Daniel Lezcano <daniel.lezcano@free.fr>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

src/lxc/commands.c

@@ -154,11 +154,32 @@ pid_t get_init_pid(const char *name)
 	return command.answer.pid;
 }
 
+int lxc_get_clone_flags(const char *name)
+{
+	struct lxc_command command = {
+		.request = { .type = LXC_COMMAND_CLONE_FLAGS },
+	};
+
+	int ret, stopped = 0;
+
+	ret = lxc_command(name, &command, &stopped);
+	if (ret < 0 && stopped)
+		return -1;
+
+	if (ret < 0) {
+		ERROR("failed to send command");
+		return -1;
+	}
+
+	return command.answer.ret;
+}
+
 extern void lxc_console_remove_fd(int, struct lxc_tty_info *);
 extern int  lxc_console_callback(int, struct lxc_request *, struct lxc_handler *);
 extern int  lxc_stop_callback(int, struct lxc_request *, struct lxc_handler *);
 extern int  lxc_state_callback(int, struct lxc_request *, struct lxc_handler *);
 extern int  lxc_pid_callback(int, struct lxc_request *, struct lxc_handler *);
+extern int  lxc_clone_flags_callback(int, struct lxc_request *, struct lxc_handler *);
 
 static int trigger_command(int fd, struct lxc_request *request,
 			   struct lxc_handler *handler)
@@ -170,6 +191,7 @@ static int trigger_command(int fd, struct lxc_request *request,
 		[LXC_COMMAND_STOP]        = lxc_stop_callback,
 		[LXC_COMMAND_STATE]       = lxc_state_callback,
 		[LXC_COMMAND_PID]         = lxc_pid_callback,
+		[LXC_COMMAND_CLONE_FLAGS] = lxc_clone_flags_callback,
 	};
 
 	if (request->type < 0 || request->type >= LXC_COMMAND_MAX)

src/lxc/commands.h

@@ -28,6 +28,7 @@ enum {
 	LXC_COMMAND_STOP,
 	LXC_COMMAND_STATE,
 	LXC_COMMAND_PID,
+	LXC_COMMAND_CLONE_FLAGS,
 	LXC_COMMAND_MAX,
 };
 
@@ -48,6 +49,7 @@ struct lxc_command {
 };
 
 extern pid_t get_init_pid(const char *name);
+extern int lxc_get_clone_flags(const char *name);
 
 extern int lxc_command(const char *name, struct lxc_command *command,
 			int *stopped);

src/lxc/start.c

@@ -279,6 +279,29 @@ int lxc_pid_callback(int fd, struct lxc_request *request,
 	return 0;
 }
 
+int lxc_clone_flags_callback(int fd, struct lxc_request *request,
+			     struct lxc_handler *handler)
+{
+	struct lxc_answer answer;
+	int ret;
+
+	answer.pid = 0;
+	answer.ret = handler->clone_flags;
+
+	ret = send(fd, &answer, sizeof(answer), 0);
+	if (ret < 0) {
+		WARN("failed to send answer to the peer");
+		return -1;
+	}
+
+	if (ret != sizeof(answer)) {
+		ERROR("partial answer sent");
+		return -1;
+	}
+
+	return 0;
+}
+
 int lxc_set_state(const char *name, struct lxc_handler *handler, lxc_state_t state)
 {
 	handler->state = state;
@@ -558,7 +581,6 @@ out_warn_father:
 
 int lxc_spawn(struct lxc_handler *handler)
 {
-	int clone_flags;
 	int failed_before_rename = 0;
 	const char *name = handler->name;
 	int pinfd;
@@ -566,10 +588,10 @@ int lxc_spawn(struct lxc_handler *handler)
 	if (lxc_sync_init(handler))
 		return -1;
 
-	clone_flags = CLONE_NEWUTS|CLONE_NEWPID|CLONE_NEWIPC|CLONE_NEWNS;
+	handler->clone_flags = CLONE_NEWUTS|CLONE_NEWPID|CLONE_NEWIPC|CLONE_NEWNS;
 	if (!lxc_list_empty(&handler->conf->network)) {
 
-		clone_flags |= CLONE_NEWNET;
+		handler->clone_flags |= CLONE_NEWNET;
 
 		/* Find gateway addresses from the link device, which is
 		 * no longer accessible inside the container. Do this
@@ -603,7 +625,7 @@ int lxc_spawn(struct lxc_handler *handler)
 	}
 
 	/* Create a process in a new set of namespaces */
-	handler->pid = lxc_clone(do_start, handler, clone_flags);
+	handler->pid = lxc_clone(do_start, handler, handler->clone_flags);
 	if (handler->pid < 0) {
 		SYSERROR("failed to fork into a new namespace");
 		goto out_delete_net;
@@ -621,7 +643,7 @@ int lxc_spawn(struct lxc_handler *handler)
 		goto out_delete_net;
 
 	/* Create the network configuration */
-	if (clone_flags & CLONE_NEWNET) {
+	if (handler->clone_flags & CLONE_NEWNET) {
 		if (lxc_assign_network(&handler->conf->network, handler->pid)) {
 			ERROR("failed to create the configured network");
 			goto out_delete_net;
@@ -651,7 +673,7 @@ int lxc_spawn(struct lxc_handler *handler)
 	return 0;
 
 out_delete_net:
-	if (clone_flags & CLONE_NEWNET)
+	if (handler->clone_flags & CLONE_NEWNET)
 		lxc_delete_network(handler);
 out_abort:
 	lxc_abort(name, handler);

src/lxc/start.h

@@ -39,6 +39,7 @@ struct lxc_handler {
 	pid_t pid;
 	char *name;
 	lxc_state_t state;
+	int clone_flags;
 	int sigfd;
 	sigset_t oldmask;
 	struct lxc_conf *conf;