Fix bug when resume to display game

Last version of implementation can't resume to display the chess board
after we stop to display it. We introduce I/O multiplexing mechanism in
order to listen to both STDIN_FILENO and device driver attribute file.
This way we can continue to listen to keyboard event even when the
kernel stops sendding data to user space.

Author: vax-r

kmldrv-user.c

@@ -4,6 +4,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/select.h>
 #include <termios.h>
 #include <unistd.h>
 
@@ -51,6 +52,32 @@ static void enableRawMode(void)
     tcsetattr(STDIN_FILENO, TCSAFLUSH, &raw);
 }
 
+static bool read_attr;
+
+static void listen_keyboard_handler(void)
+{
+    int attr_fd = open(KMLDRV_DEVICE_ATTR_FILE, O_RDWR);
+    char input;
+
+    if (read(STDIN_FILENO, &input, 1) == 1) {
+        char buf[20];
+        switch (input) {
+        case 16:
+            read(attr_fd, buf, 6);
+            buf[0] = (buf[0] - '0') ? '0' : '1';
+            read_attr = !read_attr;
+            write(attr_fd, buf, 6);
+            break;
+        case 17:
+            read(attr_fd, buf, 6);
+            buf[4] = '1';
+            write(attr_fd, buf, 6);
+            break;
+        }
+    }
+    close(attr_fd);
+}
+
 int main(int argc, char *argv[])
 {
     int c;
@@ -85,33 +112,38 @@ int main(int argc, char *argv[])
     int flags = fcntl(STDIN_FILENO, F_GETFL, 0);
     fcntl(STDIN_FILENO, F_SETFL, flags | O_NONBLOCK);
 
-    FILE *device_ptr = fopen(KMLDRV_DEVICE_FILE, "r");
     char display_buf[DRAWBUFFER_SIZE];
 
-    int attr_fd = open(KMLDRV_DEVICE_ATTR_FILE, O_WRONLY);
-    char input;
-    while (fgets(display_buf, DRAWBUFFER_SIZE, device_ptr)) {
-        printf("%s", display_buf);
-
-        if (read(STDIN_FILENO, &input, 1) == 1) {
-            switch (input) {
-            case 16:
-                char buf[20];
-                read(attr_fd, buf, 5);
-                buf[0] = (buf[0] - '0') ? '0' : '1';
-                write(attr_fd, buf, 5);
-                break;
-            case 17:
-                break;
-            }
+    fd_set readset;
+    int device_fd = open(KMLDRV_DEVICE_FILE, O_RDONLY);
+    int max_fd = device_fd > STDIN_FILENO ? device_fd : STDIN_FILENO;
+    read_attr = true;
+
+    while (1) {
+        FD_ZERO(&readset);
+        FD_SET(STDIN_FILENO, &readset);
+        FD_SET(device_fd, &readset);
+
+        int result = select(max_fd + 1, &readset, NULL, NULL, NULL);
+        if (result < 0) {
+            printf("Error with select system call\n");
+            exit(1);
+        }
+
+        if (FD_ISSET(STDIN_FILENO, &readset)) {
+            FD_CLR(STDIN_FILENO, &readset);
+            listen_keyboard_handler();
+        } else if (read_attr && FD_ISSET(device_fd, &readset)) {
+            FD_CLR(device_fd, &readset);
+            read(device_fd, display_buf, DRAWBUFFER_SIZE);
+            printf("%s", display_buf);
         }
     }
 
     disableRawMode();
     fcntl(STDIN_FILENO, F_SETFL, flags);
 
-    fclose(device_ptr);
-    close(attr_fd);
+    close(device_fd);
 
     return 0;
 }

simrupt.c

@@ -37,7 +37,7 @@ static int delay = 100; /* time (in ms) to generate an event */
 
 struct kmldrv_attr {
     char display;
-    char restart;
+    char resume;
     char end;
     rwlock_t lock;
 };
@@ -49,7 +49,7 @@ static ssize_t kmldrv_state_show(struct device *dev,
                                  char *buf)
 {
     read_lock(&attr_obj.lock);
-    int ret = snprintf(buf, 6, "%c %c %c\n", attr_obj.display, attr_obj.restart,
+    int ret = snprintf(buf, 6, "%c %c %c\n", attr_obj.display, attr_obj.resume,
                        attr_obj.end);
     read_unlock(&attr_obj.lock);
     return ret;
@@ -61,7 +61,7 @@ static ssize_t kmldrv_state_store(struct device *dev,
                                   size_t count)
 {
     write_lock(&attr_obj.lock);
-    sscanf(buf, "%c %c %c", &(attr_obj.display), &(attr_obj.restart),
+    sscanf(buf, "%c %c %c", &(attr_obj.display), &(attr_obj.resume),
            &(attr_obj.end));
     write_unlock(&attr_obj.lock);
     return count;
@@ -342,6 +342,7 @@ static void timer_handler(struct timer_list *__timer)
 
     if (win == ' ') {
         ai_game();
+        mod_timer(&timer, jiffies + msecs_to_jiffies(delay));
     } else {
         read_lock(&attr_obj.lock);
         if (attr_obj.display == '1') {
@@ -360,10 +361,16 @@ static void timer_handler(struct timer_list *__timer)
 
             wake_up_interruptible(&rx_wait);
         }
+
+        if (attr_obj.end == '0') {
+            memset(table, ' ',
+                   N_GRIDS); /* Reset the table so the game restart */
+            mod_timer(&timer, jiffies + msecs_to_jiffies(delay));
+        }
+
         read_unlock(&attr_obj.lock);
 
         pr_info("kmldrv: %c win!!!\n", win);
-        memset(table, ' ', N_GRIDS); /* Reset the table so the game restart */
     }
     tv_end = ktime_get();
 
@@ -372,8 +379,6 @@ static void timer_handler(struct timer_list *__timer)
     pr_info("kmldrv: [CPU#%d] %s in_irq: %llu usec\n", smp_processor_id(),
             __func__, (unsigned long long) nsecs >> 10);
 
-    mod_timer(&timer, jiffies + msecs_to_jiffies(delay));
-
     local_irq_enable();
 }
 
@@ -515,7 +520,7 @@ static int __init kmldrv_init(void)
     finish = 1;
 
     attr_obj.display = '1';
-    attr_obj.restart = '0';
+    attr_obj.resume = '1';
     attr_obj.end = '0';
     rwlock_init(&attr_obj.lock);
     /* Setup the timer */