delay attempt

README.md

@@ -17,9 +17,7 @@ QEMU opens up, and you can run:
 
 Each module comes from a C file under `kernel_module/`. For module usage do:
 
-    head *.c
-
-We use Buildroot's default kernel version, you can confirm it after build with:
+    head *. use Buildroot's default kernel version, you can confirm it after build with:
 
     grep BR2_LINUX_KERNEL_VERSION buildroot/.config
 
@@ -46,3 +44,4 @@ When your kernel starts crashing, get the full trace with:
         1. [fops](kernel_module/fops.c)
         1. [workqueue](kernel_module/workqueue.c)
         1. [panic](kernel_module/panic.c)
+        1. [delay](kernel_module/delay.c)

kernel_module/delay.c

@@ -0,0 +1,48 @@
+/*
+Usage:
+
+	insmod /delay.ko
+	rmmod delay
+
+dmesg prints an integer every second until rmmod.
+
+Since insmod returns, this Illustrates how the work queues are asynchronous.
+
+TODO: insmod not returning...
+*/
+
+#include <linux/delay.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/workqueue.h>
+
+MODULE_LICENSE("GPL");
+
+static struct workqueue_struct *queue;
+
+static void work_func(struct work_struct *work)
+{
+	int i = 0;
+	while (1) {
+		printk(KERN_INFO "%d\n", i);
+		usleep_range(1000000, 1000001);
+		i++;
+		if (i == 10)
+			i = 0;
+	}
+}
+
+DECLARE_WORK(work, work_func);
+
+int init_module(void)
+{
+	queue = create_workqueue("myworkqueue");
+	queue_work(queue, &work);
+	return 0;
+}
+
+void cleanup_module(void)
+{
+	cancel_work_sync(&work);
+	destroy_workqueue(queue);
+}

kernel_module/workqueue_cheat.c

@@ -1,9 +1,9 @@
 /*
 Usage:
 
-	insmod /workqueue.ko
+	insmod /workqueue_cheat.ko
 	# dmesg => worker
-	rmmod workqueue
+	rmmod workqueue_cheat
 
 Creates a separate thread. So init_module can return, but some work will still get done.