tools/xenstored: potentially split trace_io() out message

Today write_messages() will call trace_io() after having written the
complete message to the ring buffer or socket.

In case the message can't be written in one go, split it by writing
one trace entry when starting the write and one when finishing it.

In order to distinguish a complete OUT message from a split one, let the
caller of trace_io specify the prefix string ("IN", "OUT", "OUT(START)",
"OUT(END)") directly instead via an int.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>

tools/xenstored/core.c

@@ -121,7 +121,7 @@ void trace(const char *fmt, ...)
 
 static void trace_io(const struct connection *conn,
 		     const struct buffered_data *data,
-		     int out)
+		     const char *type)
 {
 	unsigned int i;
 	time_t now;
@@ -134,8 +134,7 @@ static void trace_io(const struct connection *conn,
 	tm = localtime(&now);
 
 	trace("io: %s %p (d%u) %04d%02d%02d %02d:%02d:%02d %s (",
-	      out ? "OUT" : "IN", conn, conn->id,
-	      tm->tm_year + 1900, tm->tm_mon + 1,
+	      type, conn, conn->id, tm->tm_year + 1900, tm->tm_mon + 1,
 	      tm->tm_mday, tm->tm_hour, tm->tm_min, tm->tm_sec,
 	      sockmsg_string(data->hdr.msg.type));
 	
@@ -321,43 +320,54 @@ static bool write_messages(struct connection *conn)
 {
 	int ret;
 	struct buffered_data *out;
+	bool started = false;
 
 	out = list_top(&conn->out_list, struct buffered_data, list);
 	if (out == NULL)
 		return true;
 
 	if (out->inhdr) {
+		started = !out->used;
 		ret = conn->funcs->write(conn, out->hdr.raw + out->used,
 					 sizeof(out->hdr) - out->used);
 		if (ret < 0)
-			return false;
+			goto err;
 
 		out->used += ret;
 		if (out->used < sizeof(out->hdr))
-			return true;
+			goto start;
 
 		out->inhdr = false;
 		out->used = 0;
 
 		/* Second write might block if non-zero. */
 		if (out->hdr.msg.len && !conn->domain)
-			return true;
+			goto start;
 	}
 
 	ret = conn->funcs->write(conn, out->buffer + out->used,
 				 out->hdr.msg.len - out->used);
 	if (ret < 0)
-		return false;
+		goto err;
 
 	out->used += ret;
 	if (out->used != out->hdr.msg.len)
-		return true;
+		goto start;
 
-	trace_io(conn, out, 1);
+	trace_io(conn, out, started ? "OUT" : "OUT(END)");
 
 	free_buffered_data(out, conn);
 
 	return true;
+
+ err:
+	trace_io(conn, out, "OUT(ERR)");
+	return false;
+
+ start:
+	if (started)
+		trace_io(conn, out, "OUT(START)");
+	return true;
 }
 
 static int undelay_request(void *_req)
@@ -2067,7 +2077,7 @@ static void process_message(struct connection *conn, struct buffered_data *in)
 
 	/* At least send_error() and send_reply() expects conn->in == in */
 	assert(conn->in == in);
-	trace_io(conn, in, 0);
+	trace_io(conn, in, "IN");
 
 	if ((unsigned int)type >= XS_TYPE_COUNT || !wire_funcs[type].func) {
 		eprintf("Client unknown operation %i", type);