fix swapped x and y coordinates

README.md

@@ -22,13 +22,13 @@ After loading the module, player X can write grid coordinates
 (ranging from 1 to 3, format `XY`) to `/dev/tictactoe` to make their first move:
 
 ```console
-# echo 12 > /dev/tictactoe
+# echo 22 > /dev/tictactoe
 ```
 
 After player X has made their move, player O can do the same:
 
 ```console
-# echo 22 > /dev/tictactoe
+# echo 13 > /dev/tictactoe
 ```
 
 To inspect the current state of the game, simply read from `/dev/tictactoe`:
@@ -39,9 +39,9 @@ To inspect the current state of the game, simply read from `/dev/tictactoe`:
 
 ```
 #####
+#   #
 # X #
 #O  #
-#   #
 #####
 
 It's X's turn!

tictactoe_game.c

@@ -7,7 +7,7 @@
 /*
  * Initializes a new game instance.
  */
-int tictactoe_game_init(ttt_game_t *game)
+void tictactoe_game_init(ttt_game_t *game)
 {
 	game->next_turn = 'X';
 	game->winner = 0;
@@ -16,18 +16,17 @@ int tictactoe_game_init(ttt_game_t *game)
 			game->board[x][y] = ' ';
 		}
 	}
-
-	return 0;
 }
 
 /*
- * Steps over the board, starting from position (start_x, start_y) and ending
+ * Steps over the board, starting at position (start_x, start_y) and ending
  * at the board's boundaries, checking if all cells are occupied by the same
  * player.
  *
- * start_x and start_y must lie within the board's boundaries.
+ * start_x and start_y must be within the board's boundaries.
  *
- * Returns the respective player, or '\x00' if a cell isn't occupied.
+ * Returns the respective player, or '\x00' if no single player occupies all
+ * cells within the specified streak.
  */
 static char tictactoe_game_check_streak(ttt_game_t *game, size_t start_x,
 					size_t start_y, ssize_t step_x,
@@ -112,12 +111,12 @@ static char tictactoe_game_check_winner(ttt_game_t *game)
  */
 int tictactoe_game_make_turn(ttt_game_t *game, size_t x, size_t y)
 {
-	if (game->board[x][y] != ' ') {
+	if (game->board[y][x] != ' ') {
 		pr_notice("position already occupied\n");
 		return -1;
 	}
 
-	game->board[x][y] = game->next_turn;
+	game->board[y][x] = game->next_turn;
 	game->winner = tictactoe_game_check_winner(game);
 
 	if (game->next_turn == 'X')

tictactoe_game.h

@@ -3,13 +3,13 @@
 
 #include <linux/types.h>
 
-typedef struct tictactoe_game {
+typedef struct {
 	char next_turn;
 	char winner;
 	char board[3][3];
 } ttt_game_t;
 
-int tictactoe_game_init(ttt_game_t *game);
+void tictactoe_game_init(ttt_game_t *game);
 int tictactoe_game_make_turn(ttt_game_t *game, size_t x, size_t y);
 int tictactoe_game_snprint(ttt_game_t *game, char *buf, size_t len);
 

tictactoe_internal.h

@@ -10,7 +10,7 @@
 #define tictactoe_error(format, ...) \
 	pr_err("%s: " format, __func__, ##__VA_ARGS__)
 
-typedef struct annotated_string {
+typedef struct {
 	struct mutex lock;
 	size_t len;
 	char *buf;

tictactoe_main.c

@@ -94,7 +94,7 @@ static ssize_t tictactoe_write(struct file *file, const char __user *buf,
 {
 	char *command_buf;
 	size_t count_without_lf;
-	size_t human_x, human_y;
+	size_t x, y;
 
 	if (count == 0)
 		return 0;
@@ -128,6 +128,8 @@ static ssize_t tictactoe_write(struct file *file, const char __user *buf,
 		tictactoe_game_init(tictactoe_current_game);
 		mutex_unlock(&tictactoe_mutex_current_game);
 		kfree(command_buf);
+
+		*ppos += count;
 		return count;
 	}
 
@@ -145,8 +147,8 @@ static ssize_t tictactoe_write(struct file *file, const char __user *buf,
 		}
 	}
 
-	human_x = (size_t)(command_buf[0] - '0');
-	human_y = (size_t)(command_buf[1] - '0');
+	x = (size_t)(command_buf[0] - '1');
+	y = (size_t)(command_buf[1] - '1');
 
 	kfree(command_buf);
 
@@ -163,13 +165,14 @@ static ssize_t tictactoe_write(struct file *file, const char __user *buf,
 #endif
 	}
 
-	if (tictactoe_game_make_turn(tictactoe_current_game, human_x - 1,
-				     human_y - 1)) {
+	if (tictactoe_game_make_turn(tictactoe_current_game, x, y)) {
 		mutex_unlock(&tictactoe_mutex_current_game);
 		return -EINVAL;
 	}
 
 	mutex_unlock(&tictactoe_mutex_current_game);
+
+	*ppos += count;
 	return count;
 }
 
@@ -226,12 +229,7 @@ static int __init tictactoe_init(void)
 		tictactoe_error("failed to allocate game memory\n");
 		return -EFAULT;
 	}
-	ret = tictactoe_game_init(tictactoe_current_game);
-	if (ret) {
-		mutex_unlock(&tictactoe_mutex_current_game);
-		tictactoe_error("failed to initialize game\n");
-		return -EFAULT;
-	}
+	tictactoe_game_init(tictactoe_current_game);
 	mutex_unlock(&tictactoe_mutex_current_game);
 
 	ret = misc_register(&tictactoe_dev);