add a kernel module notify chain example, compile the buildchain first before regchain

debug/Makefile

@@ -1 +1,4 @@
-obj-m += myled.o
+obj-y += myled.o
+obj-m += mycpuinfo.o
+obj-m += hello.o
+obj-m += buildchain.o regchain.o notify.o

debug/buildchain.c

@@ -0,0 +1,37 @@
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/notifier.h>
+static RAW_NOTIFIER_HEAD(test_chain);
+
+int register_test_notifier(struct notifier_block *nb)
+{
+	return raw_notifier_chain_register(&test_chain, nb);
+}
+EXPORT_SYMBOL(register_test_notifier);
+
+int unregister_test_notifier(struct notifier_block *nb)
+{
+	return raw_notifier_chain_unregister(&test_chain,nb);
+}
+EXPORT_SYMBOL(unregister_test_notifier);
+
+int test_notifier_call_chain(unsigned long val, void *v)
+{
+	return raw_notifier_call_chain(&test_chain, val, v);
+}
+EXPORT_SYMBOL(test_notifier_call_chain);
+
+static int __init init_notifier(void)
+{
+	printk("init_notifier\n");
+	return 0;
+}
+
+static void __exit exit_notifier(void)
+{
+	printk("exit_notifier\n");
+}
+
+module_init(init_notifier);
+module_exit(exit_notifier);
+MODULE_LICENSE("GPL");

debug/notify.c

@@ -0,0 +1,27 @@
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/notifier.h>
+extern int test_notifier_call_chain(unsigned long val, void*v);
+
+static int __init call_notifier(void)
+{
+	int err;
+	printk("Begin to notify:\n");
+
+
+	printk("==============================\n");
+	err = test_notifier_call_chain(1, NULL);
+	printk("==============================\n");
+	if (err)
+		printk("notifier_call_chain error\n");
+	return err;
+}
+
+static void __exit uncall_notifier(void)
+{
+	printk("Endnotify\n");
+}
+
+module_init(call_notifier);
+module_exit(uncall_notifier);
+MODULE_LICENSE("GPL");

debug/regchain.c

@@ -0,0 +1,83 @@
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/notifier.h>
+extern int unregister_test_notifier(struct notifier_block*);
+extern int register_test_notifier(struct notifier_block *nb);
+
+static int test_event1(struct notifier_block *this, unsigned long event, void *ptr)
+{
+	printk("In Event 1: Event Number is %ld\n",event);
+	return 0;
+}
+
+static int test_event2(struct notifier_block *this, unsigned long event, void *ptr)
+{
+	printk("In Event 2: Event Number is %ld\n",event);
+	return 0;
+}
+
+static int test_event3(struct notifier_block *this, unsigned long event, void *ptr)
+{
+	printk("In Event 3: Event Number is %ld\n",event);
+	return 0;
+}
+
+static struct notifier_block test_notifier1 =
+{
+	.notifier_call = test_event1,
+};
+
+static struct notifier_block test_notifier2 =
+{
+	.notifier_call = test_event2,
+};
+
+static struct notifier_block test_notifier3 =
+{
+	.notifier_call = test_event3,
+};
+
+static int __init reg_notifier(void)
+{
+	int err;
+	printk("Begin to register:\n");
+
+	err = register_test_notifier(&test_notifier1);
+	if (err)
+	{
+		printk("register test_notifier1 error\n");
+		return-1;
+	}
+	printk("register test_notifier1 completed\n");
+
+	err = register_test_notifier(&test_notifier2);
+	if (err)
+	{
+		printk("register test_notifier2 error\n");
+		return-1;
+	}
+	printk("register test_notifier2 completed\n");
+
+	err = register_test_notifier(&test_notifier3);
+	if (err)
+	{
+		printk("register test_notifier3 error\n");
+		return-1;
+	}
+	printk("register test_notifier3 completed\n");
+
+	return err;
+}
+
+static void __exit unreg_notifier(void)
+{
+	printk("Begin to unregister\n");
+	unregister_test_notifier(&test_notifier1);
+	unregister_test_notifier(&test_notifier2);
+	unregister_test_notifier(&test_notifier3);
+	printk("Unregister finished\n");
+}
+
+module_init(reg_notifier);
+module_exit(unreg_notifier);
+MODULE_LICENSE("GPL");