kernel-devel/chardev: added example

kernel and userspace example, for open, close, read, write

TODO: implement read, write

Signed-off-by: Manuel Traut <manut@linutronix.de>

4 files changed, 111 insertions, 0 deletions

diff --git a/kernel-devel/char-device/example/kernel/Makefile b/kernel-devel/char-device/example/kernel/Makefile
new file mode 100644
index 0000000..822c7d7
--- /dev/null
+++ b/kernel-devel/char-device/example/kernel/Makefile
@@ -0,0 +1,13 @@
+# If KERNELRELEASE is defined, we've been invoked from the
+# kernel build system and can use its language.
+ifneq ($(KERNELRELEASE),)
+    obj-m := huhu.o
+
+# Otherwise we were called directly from the command
+# line; invoke the kernel build system.
+else
+    KERNELDIR ?= /lib/modules/$(shell uname -r)/build
+    PWD := $(shell pwd)
+default:
+	$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
+endif
diff --git a/kernel-devel/char-device/example/kernel/huhu.c b/kernel-devel/char-device/example/kernel/huhu.c
new file mode 100644
index 0000000..99eafe7
--- /dev/null
+++ b/kernel-devel/char-device/example/kernel/huhu.c
@@ -0,0 +1,64 @@
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/fs.h>
+
+static int major;
+
+static int huhu_open(struct inode *node, struct file *f)
+{
+	printk(KERN_INFO "huhu_open: done\n");
+	return 0;
+}
+
+static int huhu_release(struct inode *node, struct file *f)
+{
+	printk(KERN_INFO "huhu_release: done\n");
+	return 0;
+}
+
+static ssize_t huhu_read(struct file *f, char __user *u, size_t s, loff_t *l)
+{
+	printk(KERN_INFO "huhu_read\n");
+	return 0;
+}
+
+static ssize_t huhu_write (struct file *f, const char __user *u, size_t s,
+	loff_t *l)
+{
+	printk(KERN_INFO "huhu_write\n");
+	return 0;
+}
+
+static const struct file_operations huhu_fops = {
+	.owner		= THIS_MODULE,
+	.open		= huhu_open,
+	.release 	= huhu_release,
+	.read		= huhu_read,
+	.write		= huhu_write,
+};
+
+static int huhu_init(void)
+{
+	major = register_chrdev (0, "huhu", &huhu_fops);
+	if (major < 0)
+	{
+		printk(KERN_ERR "huhu_init: register_chrdev failed\n");
+		return major;
+	}
+	printk(KERN_INFO "mknod /dev/huhu c %d 0", major);
+	return 0;
+}
+
+static void huhu_exit(void)
+{
+	unregister_chrdev (major, "huhu");
+	printk(KERN_INFO "huhu_exit: done\n");
+}
+
+module_init(huhu_init);
+module_exit(huhu_exit);
+
+MODULE_AUTHOR("Manuel Traut <manut@linutronix.de>");
+MODULE_DESCRIPTION("a more or less useless module using char");
+MODULE_LICENSE("GPL v2");
+MODULE_VERSION("0815");
diff --git a/kernel-devel/char-device/example/user/Makefile b/kernel-devel/char-device/example/user/Makefile
new file mode 100644
index 0000000..66a330c
--- /dev/null
+++ b/kernel-devel/char-device/example/user/Makefile
@@ -0,0 +1,6 @@
+OBJECTS=huhu.o
+
+all: $(OBJECTS)
+	gcc -o huhu $(OBJECTS)
+clean:
+	rm -f $(OBJECTS) huhu
diff --git a/kernel-devel/char-device/example/user/huhu.c b/kernel-devel/char-device/example/user/huhu.c
new file mode 100644
index 0000000..e86c126
--- /dev/null
+++ b/kernel-devel/char-device/example/user/huhu.c
@@ -0,0 +1,28 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+
+int main (int argc, char **argv)
+{
+	int ret = 0;
+	FILE *fp;
+
+	fp = fopen ("/dev/huhu", "r+");
+	if (!fp)
+	{
+		perror ("open /dev/huhu failed");
+		ret = errno;
+		goto out;
+	}
+
+	system ("/bin/lsmod | grep huhu");
+
+	ret = fclose (fp);
+	if (ret)
+	{
+		perror ("close /dev/huhu failed");
+		goto out;
+	}
+out:
+	return ret;
+}