rpc: Support gathering external file list after freezing process tree.

New 'query-ext-files' action for `criu dump` is sent after
freezing the process tree. This allows to defer gathering
the external file list when the process tree is in a stable
state and avoids race with the process creating and deleting
files.

Change-Id: Iae32149dc3992dea086f513ada52cf6863beaa1f
Signed-off-by: Michał Mirosław <emmir@google.com>

Documentation/criu.txt

@@ -155,6 +155,11 @@ not compatible with *--external* *dev*.
             notification message contains a file descriptor for
             the master pty
 
+        *query-ext-files*:::
+            called after the process tree is stopped and network is locked.
+            This hook is used only in the RPC mode. The notification reply
+            contains file ids to be added to external file list (may be empty).
+
 *--unprivileged*::
     This option tells *criu* to accept the limitations when running
     as non-root. Running as non-root requires *criu* at least to have

criu/action-scripts.c

@@ -31,6 +31,7 @@ static const char *action_names[ACT_MAX] = {
 	[ACT_POST_RESUME] = "post-resume",
 	[ACT_ORPHAN_PTS_MASTER] = "orphan-pts-master",
 	[ACT_STATUS_READY] = "status-ready",
+	[ACT_QUERY_EXT_FILES] = "query-ext-files",
 };
 
 struct script {
@@ -115,6 +116,20 @@ int rpc_send_fd(enum script_actions act, int fd)
 	return send_criu_rpc_script(act, (char *)action, rpc_sk, fd);
 }
 
+int rpc_query_external_files(void)
+{
+	int rpc_sk;
+
+	if (scripts_mode != SCRIPTS_RPC)
+		return 0;
+
+	rpc_sk = get_service_fd(RPC_SK_OFF);
+	if (rpc_sk < 0)
+		return -1;
+
+	return exec_rpc_query_external_files((char *)action_names[ACT_QUERY_EXT_FILES], rpc_sk);
+}
+
 int run_scripts(enum script_actions act)
 {
 	int ret = 0;

criu/cr-dump.c

@@ -2180,6 +2180,9 @@ int cr_dump_tasks(pid_t pid)
 	if (network_lock())
 		goto err;
 
+	if (rpc_query_external_files())
+		goto err;
+
 	if (collect_file_locks())
 		goto err;
 

criu/cr-service.c

@@ -240,6 +240,49 @@ int send_criu_rpc_script(enum script_actions act, char *name, int sk, int fd)
 	return 0;
 }
 
+int exec_rpc_query_external_files(char *name, int sk)
+{
+	int i, ret;
+	CriuNotify cn = CRIU_NOTIFY__INIT;
+	CriuResp msg = CRIU_RESP__INIT;
+	CriuReq *req;
+
+	cn.script = name;
+
+	msg.type = CRIU_REQ_TYPE__NOTIFY;
+	msg.success = true;
+	msg.notify = &cn;
+
+	ret = send_criu_msg_with_fd(sk, &msg, -1);
+	if (ret < 0)
+		return ret;
+
+	ret = recv_criu_msg(sk, &req);
+	if (ret < 0)
+		return ret;
+
+	if (req->type != CRIU_REQ_TYPE__NOTIFY || !req->notify_success) {
+		pr_err("RPC client reported script error\n");
+		return -1;
+	}
+
+	ret = 0;
+	if (req->opts)
+		for (i = 0; i < req->opts->n_external; i++) {
+			char *key = req->opts->external[i];
+			pr_info("Adding external object: %s\n", key);
+			if (add_external(key)) {
+				pr_err("Failed to add external object: %s\n", key);
+				ret = -1;
+			}
+		}
+	else
+		pr_info("RPC NOTIFY %s: no `opts` returned.\n", name);
+
+	criu_req__free_unpacked(req, NULL);
+	return ret;
+}
+
 static char images_dir[PATH_MAX];
 
 static int setup_opts_from_req(int sk, CriuOpts *req)

criu/include/action-scripts.h

@@ -17,6 +17,7 @@ enum script_actions {
 	ACT_PRE_RESUME,
 	ACT_ORPHAN_PTS_MASTER,
 	ACT_STATUS_READY,
+	ACT_QUERY_EXT_FILES,
 
 	ACT_MAX
 };
@@ -25,6 +26,8 @@ extern int add_script(char *path);
 extern int add_rpc_notify(int sk);
 extern int run_scripts(enum script_actions);
 extern int rpc_send_fd(enum script_actions, int fd);
+extern int rpc_query_external_files(void);
+extern int exec_rpc_query_external_files(char *name, int sk);
 extern int send_criu_rpc_script(enum script_actions act, char *name, int sk, int fd);
 
 #endif /* __CR_ACTION_SCRIPTS_H__ */