Ioctl

ioctl_chardev/Makefile

@@ -0,0 +1,11 @@
+obj-m = my-ioctl.o
+
+all: test.elf
+	make -C /lib/modules/$(shell uname -r)/build/ M=$(PWD) modules
+
+clean:
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
+	rm test.elf
+
+test.elf: test.c
+	$(CC) test.c -o test.elf

ioctl_chardev/README.txt

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+sudo rmmod my_ioctl
+sudo insmod my_ioctl.ko
+
+The device node is created automatically on load.
+
+Otherwise:
+    sudo mknod /dev/hello c <Major> <Minor>

ioctl_chardev/my-ioctl.c

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+#include <linux/device.h>
+#include "my-ioctl.h"
+
+MODULE_DESCRIPTION("Chardev Ioctl kernel module.");
+MODULE_VERSION("0.0.1");
+MODULE_AUTHOR("Imbus");
+MODULE_LICENSE("GPL");
+
+#define DEVICE_NAME "hello_ioctl"
+
+static int major; /* Dynamically assigned */
+static struct class *cls;
+
+static long my_ioctl(struct file *filp, unsigned int cmd, unsigned long arg);
+
+/* See: https://elixir.bootlin.com/linux/v6.14.5/source/include/linux/fs.h#L2131 */
+static struct file_operations fops = {
+	.owner = THIS_MODULE,
+	.unlocked_ioctl = my_ioctl,
+};
+
+static long my_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
+{
+	pr_info("Ioctl called by %s...\n", current->comm);
+
+	switch (cmd) {
+	case MY_IOCTL_FILL:
+		pr_info("Ioctl FILL by %s...\n", current->comm);
+		break;
+	case MY_IOCTL_WIPE:
+		pr_info("Ioctl WIPE by %s...\n", current->comm);
+		break;
+	default:
+		return -ENOTTY; // Invalid command
+	}
+	return 0;
+}
+
+static int __init demo_mod_init(void)
+{
+	major = register_chrdev(0, DEVICE_NAME, &fops);
+	if (major < 0) {
+		pr_info(DEVICE_NAME "  - Error registering chrdev\n");
+		return major;
+	}
+
+	pr_info(DEVICE_NAME " was assigned major number %d.\n", major);
+
+	cls = class_create(DEVICE_NAME);
+	device_create(cls, NULL, MKDEV(major, 0), NULL, DEVICE_NAME);
+
+	pr_info(DEVICE_NAME " created on /dev/%s\n", DEVICE_NAME);
+
+	pr_info(DEVICE_NAME " major nbr %d loaded successfully...\n", major);
+	return 0;
+}
+
+static void __exit demo_mod_exit(void)
+{
+	device_destroy(cls, MKDEV(major, 0));
+	class_destroy(cls);
+	unregister_chrdev(major, DEVICE_NAME);
+	pr_info(DEVICE_NAME " unloaded successfully...\n");
+}
+
+module_init(demo_mod_init);
+module_exit(demo_mod_exit);

ioctl_chardev/my-ioctl.h

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+#ifndef MY_IOCTL_H
+#define MY_IOCTL_H
+#include <linux/ioctl.h>
+
+/*
+ * Crucial point here, the kernel defines a set of macros for defining IOCTL numbers:
+ * 	_IO - No command
+ * 	_IOR - Read command
+ * 	_IOW - Write command
+ * 	_IORW - RW command
+ * 	_IOC - Basis of the others
+ * These macros encode the data type passed to the ioctl.
+ */
+
+#define MY_IOCTL_WIPE _IO('k', 0x01)
+#define MY_IOCTL_FILL _IO('k', 0x02) /* Name is a placeholder, fills nothing */
+
+#endif // MY-IOCTL_H

ioctl_chardev/test.c

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+#include <stdio.h>
+// #include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <linux/ioctl.h>
+#include <sys/ioctl.h>
+#include "my-ioctl.h"
+
+int main(int argc, char **argv)
+{
+	int fd;
+
+	if (argc < 2) {
+		printf("I need the file to open as an argument!\n");
+		return 0;
+	}
+
+	fd = open(argv[1], O_RDWR);
+	if (fd < 0) {
+		perror("open");
+		return 1;
+	}
+
+	if (ioctl(fd, MY_IOCTL_FILL)) {
+		perror("ioctl");
+		close(fd);
+		return 1;
+	}
+
+	if (ioctl(fd, MY_IOCTL_WIPE)) {
+		perror("ioctl");
+		close(fd);
+		return 1;
+	}
+
+	printf("ioctl successful\n");
+
+	close(fd);
+	return 0;
+}