[PATCH 8/8] trace-cmd: Acknowledge unexpected protocol messages

[Slavomir Kaslev <kaslevs@vmware.com>]

Send MSG_NOT_SUPP message back on unexpected incoming messages. This allows us
to add new commands in the future and be able to detect and handle if we're
talking with an older version of trace-cmd.

Signed-off-by: Slavomir Kaslev <kaslevs@vmware.com>
---
 tracecmd/trace-msg.c | 49 ++++++++++++++++++++++++++++++++++++--------
 1 file changed, 41 insertions(+), 8 deletions(-)

diff --git a/tracecmd/trace-msg.c b/tracecmd/trace-msg.c
index 5079d43..51d0ac8 100644
--- a/tracecmd/trace-msg.c
+++ b/tracecmd/trace-msg.c
@@ -75,7 +75,8 @@ struct tracecmd_msg_header {
 	C(TINIT,	1,	sizeof(struct tracecmd_msg_tinit)),	\
 	C(RINIT,	2,	sizeof(struct tracecmd_msg_rinit)),	\
 	C(SEND_DATA,	3,	0),					\
-	C(FIN_DATA,	4,	0),
+	C(FIN_DATA,	4,	0),					\
+	C(NOT_SUPP,	5,	0),
 
 #undef C
 #define C(a,b,c)	MSG_##a = b
@@ -370,6 +371,25 @@ static int tracecmd_msg_wait_for_msg(int fd, struct tracecmd_msg *msg)
 	return 0;
 }
 
+static int tracecmd_msg_send_notsupp(struct tracecmd_msg_handle *msg_handle)
+{
+	struct tracecmd_msg msg;
+
+	tracecmd_msg_init(MSG_NOT_SUPP, &msg);
+	return tracecmd_msg_send(msg_handle->fd, &msg);
+}
+
+static int handle_unexpected_msg(struct tracecmd_msg_handle *msg_handle,
+				 struct tracecmd_msg *msg)
+{
+	/* Don't send MSG_NOT_SUPP back if we just received one */
+	if (ntohl(msg->hdr.cmd) == MSG_NOT_SUPP)
+		return 0;
+
+	return tracecmd_msg_send_notsupp(msg_handle);
+
+}
+
 int tracecmd_msg_send_init_data(struct tracecmd_msg_handle *msg_handle,
 				unsigned int **client_ports)
 {
@@ -397,7 +417,7 @@ int tracecmd_msg_send_init_data(struct tracecmd_msg_handle *msg_handle,
 		goto out;
 
 	if (ntohl(msg.hdr.cmd) != MSG_RINIT) {
-		ret = -EINVAL;
+		ret = -EOPNOTSUPP;
 		goto error;
 	}
 
@@ -413,6 +433,8 @@ int tracecmd_msg_send_init_data(struct tracecmd_msg_handle *msg_handle,
 
 error:
 	error_operation(&msg);
+	if (ret == -EOPNOTSUPP)
+		handle_unexpected_msg(msg_handle, &msg);
 out:
 	msg_free(&msg);
 	return ret;
@@ -461,7 +483,6 @@ int tracecmd_msg_initial_setting(struct tracecmd_msg_handle *msg_handle)
 	int ret;
 	int offset = 0;
 	u32 size;
-	u32 cmd;
 
 	ret = tracecmd_msg_recv_wait(msg_handle->fd, &msg);
 	if (ret < 0) {
@@ -470,9 +491,8 @@ int tracecmd_msg_initial_setting(struct tracecmd_msg_handle *msg_handle)
 		return ret;
 	}
 
-	cmd = ntohl(msg.hdr.cmd);
-	if (cmd != MSG_TINIT) {
-		ret = -EINVAL;
+	if (ntohl(msg.hdr.cmd) != MSG_TINIT) {
+		ret = -EOPNOTSUPP;
 		goto error;
 	}
 
@@ -524,10 +544,14 @@ int tracecmd_msg_initial_setting(struct tracecmd_msg_handle *msg_handle)
 		}
 	}
 
+	msg_free(&msg);
 	return pagesize;
 
 error:
 	error_operation(&msg);
+	if (ret == -EOPNOTSUPP)
+		handle_unexpected_msg(msg_handle, &msg);
+	msg_free(&msg);
 	return ret;
 }
 
@@ -627,8 +651,12 @@ int tracecmd_msg_read_data(struct tracecmd_msg_handle *msg_handle, int ofd)
 		if (cmd == MSG_FIN_DATA) {
 			/* Finish receiving data */
 			break;
-		} else if (cmd != MSG_SEND_DATA)
-			goto error;
+		} else if (cmd != MSG_SEND_DATA) {
+			ret = handle_unexpected_msg(msg_handle, &msg);
+			if (ret < 0)
+				goto error;
+			goto next;
+		}
 
 		n = ntohl(msg.hdr.size) - MSG_HDR_LEN - ntohl(msg.hdr.cmd_size);
 		t = n;
@@ -646,6 +674,7 @@ int tracecmd_msg_read_data(struct tracecmd_msg_handle *msg_handle, int ofd)
 			s = n - t;
 		}
 
+next:
 		msg_free(&msg);
 	}
 
@@ -683,6 +712,10 @@ int tracecmd_msg_wait_close(struct tracecmd_msg_handle *msg_handle)
 			return 0;
 
 		error_operation(&msg);
+		ret = handle_unexpected_msg(msg_handle, &msg);
+		if (ret < 0)
+			goto error;
+
 		msg_free(&msg);
 	}
 
-- 
2.19.1