Couple of improvements in the daemon (common + lvmetad) code:

- some client-side memory leak fixes
- announce and check protocols and protocol versions

daemons/common/daemon-client.c

@@ -9,7 +9,7 @@
 #include <errno.h> // ENOMEM
 
 daemon_handle daemon_open(daemon_info i) {
-	daemon_handle h = { .protocol = 0 };
+	daemon_handle h = { .protocol_version = 0 };
 	struct sockaddr_un sockaddr;
 
 	if ((h.socket_fd = socket(PF_UNIX, SOCK_STREAM /* | SOCK_NONBLOCK */, 0)) < 0) {
@@ -24,10 +24,28 @@ daemon_handle daemon_open(daemon_info i) {
 		perror("connect");
 		goto error;
 	}
+
+	daemon_reply r = daemon_send_simple(h, "hello", NULL);
+	if (r.error || strcmp(daemon_reply_str(r, "response", "unknown"), "OK"))
+		goto error;
+
+	h.protocol = daemon_reply_str(r, "protocol", NULL);
+	if (h.protocol)
+		h.protocol = dm_strdup(h.protocol); /* keep around */
+	h.protocol_version = daemon_reply_int(r, "version", 0);
+
+	if (i.protocol && (!h.protocol || strcmp(h.protocol, i.protocol)))
+		goto error;
+	if (i.protocol_version && h.protocol_version != i.protocol_version)
+		goto error;
+
+	daemon_reply_destroy(r);
 	return h;
 error:
 	if (h.socket_fd >= 0)
 		close(h.socket_fd);
+	if (r.cft)
+		daemon_reply_destroy(r);
 	h.socket_fd = -1;
 	return h;
 }
@@ -43,6 +61,7 @@ daemon_reply daemon_send(daemon_handle h, daemon_request rq)
 
 	assert(rq.buffer);
 	write_buffer(h.socket_fd, rq.buffer, strlen(rq.buffer));
+	dm_free(rq.buffer);
 
 	if (read_buffer(h.socket_fd, &reply.buffer)) {
 		reply.cft = dm_config_from_string(reply.buffer);
@@ -55,6 +74,7 @@ daemon_reply daemon_send(daemon_handle h, daemon_request rq)
 void daemon_reply_destroy(daemon_reply r) {
 	if (r.cft)
 		dm_config_destroy(r.cft);
+	dm_free(r.buffer);
 }
 
 daemon_reply daemon_send_simple(daemon_handle h, const char *id, ...)
@@ -72,10 +92,10 @@ daemon_reply daemon_send_simple(daemon_handle h, const char *id, ...)
 		return err;
 
 	repl = daemon_send(h, rq);
-	dm_free(rq.buffer);
 	return repl;
 }
 
 void daemon_close(daemon_handle h)
 {
+	dm_free((char *)h.protocol);
 }

daemons/common/daemon-client.h

@@ -19,13 +19,21 @@
 
 typedef struct {
 	int socket_fd; /* the fd we use to talk to the daemon */
-	int protocol;  /* version of the protocol the daemon uses */
+	const char *protocol;
+	int protocol_version;  /* version of the protocol the daemon uses */
 } daemon_handle;
 
 typedef struct {
 	const char *path; /* the binary of the daemon */
 	const char *socket; /* path to the comms socket */
 	unsigned autostart:1; /* start the daemon if not running? */
+
+	/*
+	 * If the following are not NULL/0, an attempt to talk to a daemon which
+	 * uses a different protocol or version will fail.
+	 */
+	const char *protocol;
+	int protocol_version;
 } daemon_info;
 
 typedef struct {

daemons/common/daemon-server.c

@@ -239,6 +239,19 @@ static int buffer_line(const char *line, void *baton) {
 	return 0;
 }
 
+static response builtin_handler(daemon_state s, client_handle h, request r)
+{
+	const char *rq = daemon_request_str(r, "request", "NONE");
+
+	if (!strcmp(rq, "hello")) {
+		return daemon_reply_simple("OK", "protocol = %s", s.protocol ?: "default",
+					   "version = %d", s.protocol_version, NULL);
+	}
+
+	response res = { .buffer = NULL, .error = EPROTO };
+	return res;
+}
+
 static void *client_thread(void *baton)
 {
 	struct thread_baton *b = baton;
@@ -252,7 +265,11 @@ static void *client_thread(void *baton)
 		req.cft = dm_config_from_string(req.buffer);
 		if (!req.cft)
 			fprintf(stderr, "error parsing request:\n %s\n", req.buffer);
-		res = b->s.handler(b->s, b->client, req);
+
+		res = builtin_handler(b->s, b->client, req);
+
+		if (res.error == EPROTO) /* Not a builtin, delegate to the custom handler. */
+			res = b->s.handler(b->s, b->client, req);
 
 		if (!res.buffer) {
 			dm_config_write_node(res.cft->root, buffer_line, &res);

daemons/common/daemon-server.h

@@ -78,6 +78,9 @@ typedef struct daemon_state {
 	const char *name;
 	const char *pidfile;
 	const char *socket_path;
+	const char *protocol;
+	int protocol_version;
+
 	int log_level;
 	handle_request handler;
 	int (*daemon_init)(struct daemon_state *st);

daemons/lvmetad/lvmetad-client.h

@@ -64,6 +64,8 @@ static inline daemon_handle lvmetad_open(const char *socket)
 	daemon_info lvmetad_info = {
 		.path = "lvmetad",
 		.socket = socket ?: DEFAULT_RUN_DIR "/lvmetad.socket",
+		.protocol = "lvmetad",
+		.protocol_version = 1,
 		.autostart = 0
 	};
 

daemons/lvmetad/lvmetad-core.c

@@ -984,6 +984,8 @@ int main(int argc, char *argv[])
 		s.socket_path = DEFAULT_RUN_DIR "/lvmetad.socket";
 	s.pidfile = DEFAULT_RUN_DIR "/lvmetad.pid";
         s.log_level = 0;
+	s.protocol = "lvmetad";
+	s.protocol_version = 1;
 
 	// use getopt_long
 	while ((opt = getopt(argc, argv, "?fhVdRs:")) != EOF) {