get device id correctly

sway/input/input-manager.c

@@ -5,6 +5,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <libinput.h>
+#include <math.h>
 #include "sway/config.h"
 #include "sway/input/input-manager.h"
 #include "sway/input/seat.h"
@@ -33,6 +34,13 @@ static struct sway_seat *input_manager_get_seat(
 	return sway_seat_create(input, seat_name);
 }
 
+static inline int strlen_num(int num) {
+	if (num == 0) {
+		return 2;
+	}
+	return (int)((ceil(log10(abs(num)))+2));
+}
+
 static char *get_device_identifier(struct wlr_input_device *device) {
 	int vendor = device->vendor;
 	int product = device->product;
@@ -46,9 +54,12 @@ static char *get_device_identifier(struct wlr_input_device *device) {
 		}
 	}
 
-	sway_log(L_DEBUG, "rewritten name %s", name);
+	int len =
+		(strlen(name) +
+		 strlen_num(device->vendor) +
+		 strlen_num(device->product) +
+		 3) * sizeof(char);
 
-	int len = strlen(name) + sizeof(char) * 6;
 	char *identifier = malloc(len);
 	if (!identifier) {
 		sway_log(L_ERROR, "Unable to allocate unique input device name");