failed fops attempt

README.md

@@ -319,6 +319,7 @@ But TODO I don't think you can see where you are in the kernel source code and l
             1.  [panic](kernel_module/panic.c)
         1.  [params](kernel_module/params.c)
         1.  [fops](kernel_module/fops.c)
+            1. [ioctl](ioctl.c)
             1. [poll](poll.c)
         1.  Asynchronous
             1. [workqueue](kernel_module/workqueue.c)

kernel_module/fops.c

@@ -28,10 +28,9 @@ Here we use debugfs.
 MODULE_LICENSE("GPL");
 
 static struct dentry *dir;
-
 static char data[] = {'a', 'b', 'c', 'd'};
 
-static int fop_open(struct inode *inode, struct file *file)
+static int open(struct inode *inode, struct file *filp)
 {
 	printk(KERN_INFO "open\n");
 	return 0;
@@ -42,7 +41,7 @@ static int fop_open(struct inode *inode, struct file *file)
  *      Then when userland reads the same file descriptor again,
  *      we start from that point instead.
  * */
-static ssize_t fop_read(struct file *file, char __user *buf, size_t len, loff_t *off)
+static ssize_t read(struct file *filp, char __user *buf, size_t len, loff_t *off)
 {
 	ssize_t ret;
 	printk(KERN_INFO "read\n");
@@ -67,7 +66,7 @@ static ssize_t fop_read(struct file *file, char __user *buf, size_t len, loff_t
  * we must return ENOSPC if the user tries to write more
  * than the size of our buffer. Otherwise, Bash > just
  * keeps trying to write to it infinitely. */
-static ssize_t fop_write(struct file *file, const char __user *buf, size_t len, loff_t *off)
+static ssize_t write(struct file *filp, const char __user *buf, size_t len, loff_t *off)
 {
 	ssize_t ret;
 	printk(KERN_INFO "write\n");
@@ -96,13 +95,13 @@ static ssize_t fop_write(struct file *file, const char __user *buf, size_t len,
 Called on the last close:
 http://stackoverflow.com/questions/11393674/why-is-the-close-function-is-called-release-in-struct-file-operations-in-the-l
 */
-static int fop_release (struct inode *inode, struct file *file)
+static int release (struct inode *inode, struct file *filp)
 {
 	printk(KERN_INFO "release\n");
 	return 0;
 }
 
-static loff_t fop_llseek(struct file *filp, loff_t off, int whence)
+static loff_t llseek(struct file *filp, loff_t off, int whence)
 {
 	loff_t newpos;
 	printk(KERN_INFO "llseek\n");
@@ -129,26 +128,17 @@ static loff_t fop_llseek(struct file *filp, loff_t off, int whence)
 }
 
 static const struct file_operations fops = {
-	.llseek = fop_llseek,
-	.open = fop_open,
-	.read = fop_read,
-	.release = fop_release,
-	.write = fop_write,
+	.llseek = llseek,
+	.open = open,
+	.read = read,
+	.release = release,
+	.write = write,
 };
 
 static int myinit(void)
 {
-	struct dentry *file;
 	dir = debugfs_create_dir("lkmc_fops", 0);
-	if (!dir) {
-		printk(KERN_ALERT "debugfs_create_dir failed");
-		return -1;
-	}
-	file = debugfs_create_file("f", 0666, dir, NULL, &fops);
-	if (!file) {
-		printk(KERN_ALERT "debugfs_create_file failed");
-		return -1;
-	}
+	debugfs_create_file("f", 0666, dir, NULL, &fops);
 	return 0;
 }
 

kernel_module/ioctl.c

@@ -0,0 +1,36 @@
+/*
+Give integer and a pointer to the kernel, and get one positive integer out.
+*/
+
+#include <linux/debugfs.h>
+#include <linux/module.h>
+#include <linux/printk.h> /* printk */
+
+MODULE_LICENSE("GPL");
+
+static struct dentry *dir;
+
+static long unlocked_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
+{
+	pr_info("cmd = %u\n", cmd);
+	return cmd + 1;
+}
+
+static const struct file_operations fops = {
+	.unlocked_ioctl = unlocked_ioctl
+};
+
+static int myinit(void)
+{
+	dir = debugfs_create_dir("lkmc_ioctl", 0);
+	debugfs_create_file("f", 0666, dir, NULL, &fops);
+	return 0;
+}
+
+static void myexit(void)
+{
+	debugfs_remove_recursive(dir);
+}
+
+module_init(myinit)
+module_exit(myexit)

kernel_module/test/ioctl.c

@@ -0,0 +1,33 @@
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <errno.h>
+
+int main(int argc, char **argv)
+{
+	int fd, ret;
+
+	if (argc < 4) {
+		puts("Usage: ./prog <ioctl-file> <cmd> <arg>");
+		return EXIT_FAILURE;
+	}
+	fd = open(argv[1], O_RDONLY);
+	if (fd == -1) {
+		perror("open");
+		return EXIT_FAILURE;
+	}
+	ret = ioctl(fd, strtoul(argv[2], NULL, 10), argv[3]);
+	if (ret == -1) {
+		perror("ioctl");
+		return EXIT_FAILURE;
+	}
+	printf("ret = %d\n", ret);
+	printf("errno = %d\n", errno);
+	close(fd);
+	return EXIT_SUCCESS;
+}

rootfs_overlay/ioctl.sh

@@ -0,0 +1,7 @@
+#!/bin/sh
+set -e
+insmod /ioctl.ko
+cd /sys/kernel/debug/lkmc_ioctl/
+/ioctl.out f 2 1
+#/ioctl.out f 1 0
+rmmod ioctl