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Hello World

Implement hello world driver based on Linux Device Driver Chapter2.

Make as below,

  root@peter-VirtualBox:/home/peter/develop/linux/drivers/char/hello# ll
  total 16
  drwxr-xr-x  2 root   root   4096  8月 26 15:58 ./
  drwxrwxr-x 13 peter peter 4096  8月 26 15:26 ../
  -rw-r--r--  1 root   root    292  8月 26 15:27 hello.c
  -rw-r--r--  1 root   root    194  8月 26 15:55 Makefile
  root@peter-VirtualBox:/home/peter/develop/linux/drivers/char/hello# make
  make -C /lib/modules/4.0.0-rc1+/build M=/home/peter/develop/linux/drivers/char/hello modules
  make[1]: Entering directory `/home/peter/develop/linux'
    CC [M]  /home/peter/develop/linux/drivers/char/hello/hello.o
    Building modules, stage 2.
    MODPOST 1 modules
    CC      /home/peter/develop/linux/drivers/char/hello/hello.mod.o
    LD [M]  /home/peter/develop/linux/drivers/char/hello/hello.ko
  make[1]: Leaving directory `/home/peter/develop/linux'
  root@peter-VirtualBox:/home/peter/develop/linux/drivers/char/hello# ll
  total 100
  drwxr-xr-x  3 root   root    4096  8月 26 15:58 ./
  drwxrwxr-x 13 peter peter  4096  8月 26 15:26 ../
  -rw-r--r--  1 root   root     292  8月 26 15:27 hello.c
  -rw-r--r--  1 root   root    1999  8月 26 15:58 hello.ko
  -rw-r--r--  1 root   root     293  8月 26 15:58 .hello.ko.cmd
  -rw-r--r--  1 root   root     454  8月 26 15:58 hello.mod.c
  -rw-r--r--  1 root   root    1432  8月 26 15:58 hello.mod.o
  -rw-r--r--  1 root   root   25872  8月 26 15:58 .hello.mod.o.cmd
  -rw-r--r--  1 root   root    1152  8月 26 15:58 hello.o
  -rw-r--r--  1 root   root   25764  8月 26 15:58 .hello.o.cmd
  -rw-r--r--  1 root   root     194  8月 26 15:55 Makefile
  -rw-r--r--  1 root   root      62  8月 26 15:58 modules.order
  -rw-r--r--  1 root   root       0  8月 26 15:58 Module.symvers
  drwxr-xr-x  2 root   root    4096  8月 26 15:58 .tmp_versions/
  root@peter-VirtualBox:/home/peter/develop/linux/drivers/char/hello# insmod ./hello.ko 
  insmod: ERROR: could not insert module ./hello.ko: File exists
  root@peter-VirtualBox:/home/peter/develop/linux/drivers/char/hello# rmmod hello.ko
  root@peter-VirtualBox:/home/peter/develop/linux/drivers/char/hello# insmod ./hello.ko 
  root@peter-VirtualBox:/home/peter/develop/linux/drivers/char/hello# 

view the log from /var/log/syslog,

  Aug 26 15:50:05 peter-VirtualBox kernel: [ 6641.824580] Hello, world
  Aug 26 15:55:01 peter-VirtualBox CRON[16299]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
  Aug 26 16:00:06 peter-VirtualBox kernel: [ 7242.631977] Goodbye, cruel world
  Aug 26 16:00:09 peter-VirtualBox kernel: [ 7245.632334] Hello, world

ioctl

ioctl() is one of the remaining parts of the kernel which runs under the Big Kernel Lock (BKL). In the past, the usage of the BKL has made it possible for long-running ioctl() methods to create long latencies for unrelated processes.

What is the difference between ioctl(), unlocked_ioctl() and compat_ioctl()?

http://unix.stackexchange.com/questions/4711/what-is-the-difference-between-ioctl-unlocked-ioctl-and-compat-ioctl

Kconfig

FAQ

How to deal with driver build failed?

Double check .config to make sure that the .config is compatible with current platform and kernel version.

Reference

Hello World