Bryan Brattlof - Eudyptula Challenge

"Beauty is in the eye of the beholder"

if (err)
        return -ENOMEM;

if (err) {
        pr_dbg("Failed to allocate memory");
        return -ENOMEM;
}

int do_something_cool(void)
{
        return something_cool == DONE;
}

$ ./scripts/checkpatch.pl --help

$ ./scripts/checkpatch.pl -f ~/eudyptupla/tasks/04/coding_style.c
...
total: 1 errors, 1 warnings, 1 checks, 35 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-inplace.

eudyptupla/tasks/04/coding_style.c has style problems, please review.

$ ./scripts/checkpatch.pl --strict --codespell -f ~/eudyptula ...

$ make -j `getconf _NPROCESSORS_ONLN` EXTRAVERSION=-eudyptula

-EXTRAVERSION = -rc1
+EXTRAVERSION = -eudyptula

$ make -j `getconf _NPROCESSORS_ONLN`

$ make menuconfig

$ make -j `getconf _NPROCESSORS_ONLN`

$ sudo apt install build-essential libncurses-dev bison flex libssl-dev libelf-dev

$ git clone https://git.kernel.org/pub/scm/linux ...

$ cp /boot/config-`uname -r` .config

$ yes "" | make oldconfig

$ make menuconfig

$ make -j `getconf _NPROCESSORS_ONLN` CONFIG_LOCALVERSION_AUTO=y LOCALVERSION=-eudyptula

CONFIG_LOCALVERSION_AUTO=y LOCALVERSION=-eudyptula

linux-image-5.8.0-rc4-eudyptula-00381-g1df0d8960499

$ sudo make modules_install install

$ make deb-pkg

sudo dpkg -i ../*.deb

$ uname -r
linux-image-5.8.0-rc4-eudyptula-00381-g1df0d8960499

#include <linux/kernel.h>  /* for KERN_DEBUG */
#include <linux/module.h>  /* for all kernel modules */

int init_module(void)
{
        printk(KERN_DEBUG "Hello World.\n");
        return 0; /* init_module loaded successfully */
}

void cleanup_module(void)
{
        printk(KERN_DEBUG "oh, the rest is silence.\n");
}

printk(KERN_DEBUG "Hello World.\n");

printk("\001" "7" "Hello World.\n");

printk("\0017Hello World.\n");

$ ls -l
total 8
-rw-rw-r-- 1 me us 903 Jul  5 00:00 hello-world.c
-rw-rw-r-- 1 me us 167 Jul  5 00:00 Makefile

obj-m += hello-world.o

all:
    ${MAKE} -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
    ${MAKE} -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

$ make
make -C /lib/modules/4.15.0-108-generic/build M=/home/me/src/eudyptula ...
/tasks/01 modules
make[1]: Entering directory '/usr/src/linux-headers-4.15.0-108-generic'
  CC [M]  /home/me/src/eudyptula/tasks/01/hello-world.o
  Building modules, stage 2.
  MODPOST 1 modules
WARNING: modpost: missing MODULE_LICENSE() in /home/me/src/eudyptula ...
see include/linux/module.h for more information
  CC      /home/me/src/eudyptula/tasks/01/hello-world.mod.o
  LD [M]  /home/me/src/eudyptula/tasks/01/hello-world.ko
make[1]: Leaving directory '/usr/src/linux-headers-4.15.0-108-generic'

$ modinfo hello-world.ko
filename:       /home/me/src/eudyptula/tasks/01/hello-world.ko
srcversion:     18005133D4ECFCDD12928D8
depends:
retpoline:      Y
name:           hello_world
vermagic:       4.15.0-108-generic SMP mod_unload

$ sudo insmod hello-world.ko

$ dmesg | tail -1
[241745.247591] Hello World.

$ sudo rmmod hello_world

$ dmesg | tail -1
[241751.401232] oh, the rest is silence.

$ tools/debugging/kernel-chktaint
Kernel is "tainted" for the following reasons:
 * proprietary module was loaded (#0)
 * kernel issued warning (#9)
 * externally-built ('out-of-tree') module was loaded  (#12)
 * unsigned module was loaded (#13)
For a more detailed explanation of the various taint flags see
 Documentation/admin-guide/tainted-kernels.rst in the the Linux kernel sources
 or https://kernel.org/doc/html/latest/admin-guide/tainted-kernels.html
Raw taint value as int/string: 12801/'P        W  OE    '

MODULE_LICENSE("MIT");
MODULE_AUTHOR("Bryan Brattlof <email@example.com>");
MODULE_DESCRIPTION("A Hello World Driver");
MODULE_SUPPORTED_DEVICE("testdevice");

$ make
make -C /lib/modules/4.15.0-108-generic/build M=/home/me/src/eudyptula ...
make[1]: Entering directory '/usr/src/linux-headers-4.15.0-108-generic'
  CC [M]  /home/me/src/eudyptula/tasks/01/hello-world.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC      /home/me/src/eudyptula/tasks/01/hello-world.mod.o
  LD [M]  /home/me/src/eudyptula/tasks/01/hello-world.ko
make[1]: Leaving directory '/usr/src/linux-headers-4.15.0-108-generic'

-int init_module(void)
+static int __init hello_world_init(void)
 {
         printk(KERN_DEBUG "Hello World.\n");
         return 0; /* init_module loaded successfully */
 }

-void cleanup_module(void)
+static void __exit hello_world_exit(void)
 {
         printk(KERN_DEBUG "oh, the rest is silence.\n");
 }

module_init(hello_world_init);
module_exit(hello_world_exit);

 static int __init hello_world_init(void)
 {
-    printk(KERN_DEBUG "Hello World.\n");
+    pr_debug("Hello World.\n");
     return 0; /* means init_module loaded successfully */
 }

 static void __exit hello_world_exit(void)
 {
-    printk(KERN_DEBUG "oh, the rest is silence.\n");
+    pr_debug("oh, the rest is silence.\n");
 }

Bryan Brattlof - Eudyptula Challenge

The Linux Kernel Coding Style

Task No.4

Executive Summary of the Linux Kernel Coding Style

scripts/checkpatch.pl

Wrapping Up

Modify The Linux Kernel

Task No.3

Override Directives

Modify the Makefile

Modify menuconfig

Building The Linux Kernel

Task No.2

Build Tools

Cloning

Configuring

Configuration Plagiarism

Configuring By Hand

Building

Installing

Ubuntu/Debian Weirdness

The Hello World Kernel Module

Task No.1

What Is A Module

Chiseling A Cave Module

printk() != printf()

Making A Kernel Module

Kbuild Makefile

Goal Definitions

Convenience Targets

Installing A Kernel Module

Installing the Module

Removing the Module

Kernel Taint

Licensing & Documentation

Updating the Module

module_init() & module_exit()

init & exit

pr_debug()

Wrapping Up

Bryan Brattlof - Eudyptula Challenge

The Linux Kernel Coding Style

Task No.4

Executive Summary of the Linux Kernel Coding Style

scripts/checkpatch.pl

Wrapping Up

Modify The Linux Kernel

Task No.3

Override Directives

Modify the Makefile

Modify menuconfig

Building The Linux Kernel

Task No.2

Build Tools

Cloning

Configuring

Configuration Plagiarism

Configuring By Hand

Building

Installing

Ubuntu/Debian Weirdness

The Hello World Kernel Module

Task No.1

What Is A Module

Chiseling A Cave Module

printk() != printf()

Making A Kernel Module

Kbuild Makefile

Goal Definitions

Convenience Targets

Installing A Kernel Module

Installing the Module

Removing the Module

Kernel Taint

Licensing & Documentation

Updating the Module

module_init() & module_exit()

__init & __exit

pr_debug()

Wrapping Up

init & exit