feat: add timed kernel thread

kernel/kmod.c

@@ -5,11 +5,13 @@
 #include <linux/vmalloc.h>
 #include <linux/uaccess.h>
 #include <linux/hrtimer.h>
+#include <linux/kthread.h>
 #include "../common/include/message.h"
 
 #define DEVICE_NAME "amogus"
 #define CLASS_NAME "amogus_class"
 
+#define SLOTS 4
 #define SLOT_INTERVAL_NS 250000
 
 static int major_number;
@@ -21,6 +23,13 @@ static message_t* message;
 static struct hrtimer timer;
 static ktime_t interval;
 
+static struct task_struct *timed_thread;
+
+static DECLARE_WAIT_QUEUE_HEAD(wq);
+static atomic_t wake_counter = ATOMIC_INIT(0);
+
+static int slot = 0;
+
 static int device_open(struct inode *inode, struct file *file)
 {
     return 0;
@@ -55,10 +64,26 @@ static const struct file_operations fops = {
 };
 
 static enum hrtimer_restart timer_callback(struct hrtimer *timer) {
+    atomic_inc(&wake_counter);
+    wake_up_interruptible(&wq);
+
     hrtimer_forward_now(timer, interval);
     return HRTIMER_RESTART;
 }
 
+static int timed_thread_fn(void *args) {
+    while (!kthread_should_stop()) {
+        wait_event_interruptible(wq, atomic_read(&wake_counter) > 0);
+        atomic_dec(&wake_counter);
+
+        if (slot == 0) {}
+
+        slot = (slot + 1) % SLOTS;
+    }
+
+    return 0;
+}
+
 static int __init lkm_init(void)
 {
     dev_t dev;
@@ -110,6 +135,20 @@ static int __init lkm_init(void)
     timer.function = timer_callback;
     hrtimer_start(&timer, interval, HRTIMER_MODE_REL);
 
+    timed_thread = kthread_run(timed_thread_fn, NULL, "timed_thread");
+    if (IS_ERR(timed_thread)) {
+        vfree(message);
+        cdev_del(&mycdev);
+        device_destroy(class, MKDEV(major_number, 0));
+        class_destroy(class);
+        unregister_chrdev_region(MKDEV(major_number, 0), 1);
+
+        hrtimer_cancel(&timer);
+
+        printk(KERN_ALERT "Failed to create timed thread\n");
+        return -1;
+    }
+
     return 0;
 }