madsonic / dev-driver

Penguin driving a car

1a

module_init: when the module is loaded by the kernel

module_exit: when the module is removed from memory / unloaded

1b

This part assumes that your module is a driver otherwise it is a matter of building your module outside the kernel directory, with the target destination set to the kernel source directory

building

update modules Makefile to include your module. e.g. the hello module lives in linux-4.15/drivers/hello/

Append the Makefile in drivers/ with obj-m += hello/

Then append the Makefile in hello/ with obj-m += hello.o

finally build with

$ make modules

installing module

as per the previous assignment, we can install the module with

$ make modules_install

loading module

not sure if 'installing the module' meant 'loading' so this is included for completeness sake

$ cd /lib/modules/4.15.0/kernel/drivers/hello/ #or where ever your install your module
$ insmod hello.ko

1c

1d

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
+ #include <linux/moduleparam.h>

MODULE_LICENSE("GPL");

+ static char *who = "world";
+ module_param(who, charp, S_IRUGO);

static int hello_init(void) {
-    printk(KERN_ALERT "Hello, world\n");
+    printk(KERN_ALERT "Hello, %s\n", who);
    return 0;
}

static void hello_exit(void) {
-    printk(KERN_ALERT "Goodbye, cruel world\n");
+    printk(KERN_ALERT "Goodbye, %s\n", who);
}

module_init(hello_init);
module_exit(hello_exit);

Note: dmesg -c was called prior to loading the module

2a

$ mknod /dev/onebyte c 61 0

2b

2c

Code for read

static ssize_t onebyte_read(struct file *filep, char __user *buf, size_t count, loff_t *f_pos) {
    if (*f_pos + count > CAPACITY) {
        count = CAPACITY - *f_pos;
    }

    if (copy_to_user(buf, onebyte_data, count) != 0) {
        return -EFAULT;
    }
    *f_pos += count;
    return count;
}

Code for write

static ssize_t onebyte_write(struct file *filep, const char __user *buf, size_t count, loff_t *f_pos) {
    if (*f_pos > CAPACITY) {
        return 0;
    }

    if (copy_from_user(onebyte_data, buf, CAPACITY) != 0) {
        return -EFAULT;
    }


    if (count > CAPACITY) {
        return -ENOSPC;
    }

    return CAPACITY;
}

Test cases

Commits log

View Github repo