Fix initialization bug (repeating enter key #9)

When starting keyd the last key event gets dropped. This happens because
keyd grabs the keyboard before the key up event can get generated. In most
cases this is benign and remedied by hitting the last key that was held
(usually enter) but can cause pathological behaviour in certain libinput
configurations. This patch causes keyd to wait for a neutral keyboard
state before proceeding with initialization.

src/main.c

@@ -45,7 +45,7 @@
 #define LOG_FILE "/var/log/keyd.log" //Only used when running as a daemon.
 
 #ifdef DEBUG
-	#define dbg(...) warn(__VA_ARGS__)
+	#define dbg(fmt, ...) warn("%s:%d: "fmt, __FILE__, __LINE__, ## __VA_ARGS__)
 #else
 	#define dbg(...)
 #endif
@@ -78,7 +78,7 @@ static void warn(char *fmt, ...)
 	fprintf(stderr, "\n");
 }
 
-static void die(char *fmt, ...)
+static void _die(char *fmt, ...)
 {
 	va_list args; 
 	va_start(args, fmt);
@@ -89,6 +89,8 @@ static void die(char *fmt, ...)
 	exit(-1);
 }
 
+#define die(fmt, ...) _die("%s:%d: "fmt, __FILE__, __LINE__, ## __VA_ARGS__)
+
 static int is_keyboard(struct udev_device *dev) 
 {
 	int is_keyboard = 0;
@@ -402,6 +404,70 @@ static const char *evdev_device_name(const char *devnode)
 	return name;
 }
 
+//Block on the given keyboard nodes until no keys are depressed.
+void await_keyboard_neutrality(char **devs, int n)
+{
+	int fds[MAX_KEYBOARDS];
+	int maxfd = 0;
+	int i;
+
+	dbg("Awaiting keyboard neutrality.");
+	for(i = 0;i < n;i++) {
+		if((fds[i] = open(devs[i], O_RDONLY | O_NONBLOCK)) < 0)
+			die("open");
+
+		if(fds[i] > maxfd)
+			maxfd = fds[i];
+	}
+
+	//There is a race condition here since it is possible for a key down
+	//event to be generated before keyd is launched, in that case we hope a
+	//repeat event is generated within the first 300ms. If we miss the
+	//keydown event and the repeat event is not generated within the first
+	//300ms it is possible for this to yield a false positive. In practice
+	//this seems to work fine. Given the stateless nature of evdev I am not 
+	//aware of a better way to achieve this.
+
+	while(1) {
+		struct timeval tv = {
+			.tv_usec = 300000
+		};
+
+		struct input_event ev;
+		int i;
+		fd_set fdset;
+
+		FD_ZERO(&fdset);
+		for(i = 0;i < n;i++)
+			FD_SET(fds[i], &fdset);
+
+		select(maxfd+1, &fdset, NULL, NULL, &tv);
+
+		for(i = 0;i < n;i++) {
+			if(FD_ISSET(fds[i], &fdset)) {
+				while(read(fds[i], &ev, sizeof ev) > 0) {
+					if(ev.type == EV_KEY) {
+						keystate[ev.code] = ev.value;
+						dbg("keystate[%d]: %d", ev.code, ev.value);
+					}
+				}
+			}
+		}
+
+		for(i = 0;i < KEY_CNT;i++)
+			if(keystate[i])
+				break;
+
+		if(i == KEY_CNT)
+			break;
+	}
+
+	for(i = 0;i < n;i++)
+		close(fds[i]);
+
+	dbg("Keyboard neutrality achieved");
+}
+
 static int manage_keyboard(const char *devnode)
 {
 	int fd;
@@ -555,12 +621,13 @@ static void main_loop()
 	struct keyboard *kbd;
 	int monfd;
 
-	int i, sz;
+	int i, n;
 	char *devs[MAX_KEYBOARDS];
 
-	get_keyboard_nodes(devs, &sz);
+	get_keyboard_nodes(devs, &n);
+	await_keyboard_neutrality(devs, n);
 
-	for(i = 0;i < sz;i++) {
+	for(i = 0;i < n;i++) {
 		manage_keyboard(devs[i]);
 		free(devs[i]);
 	}