【Linux】【Kernel】一个简单的内核模块例子

1.本地主机的参数

zhangjun@zhangjun-virtual-machine:~$ uname -a

Linux zhangjun-virtual-machine 4.4.0-31-generic #50~14.04.1-Ubuntu SMP Wed Jul 13 01:07:32 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

zhangjun@zhangjun-virtual-machine:~$ ls /usr/src/linux-headers-4.4.0-31-generic/arch Documentation include Kconfig mm scripts tools zfs

block drivers init kernel Module.symvers security ubuntu

certs firmware ipc lib net sound usr

crypto fs Kbuild Makefile samples spl virt

2.编写内核模块文件

编写自己的内核模块文件myModule.c，内容如下：

#include <linux/kernel.h>

#include <linux/module.h>

#include <linux/types.h>

static int __init myModule_init(void)

{

printk(KERN_INFO"myModule init.\r\n");

return 0;

}

static void __exit myModule_exit(void)

{

printk(KERN_INFO"myModule exit.\r\n");

}

module_init(myModule_init);

module_exit(myModule_exit);

MODULE_LICENSE("GPL");

3.编写Makefile

#kernel代码的路径

KERN_DIR = /usr/src/linux-headers-4.4.0-31-generic/

all:

make -C $(KERN_DIR) M=`pwd` modules

clean:

make -C $(KERN_DIR) M=`pwd` modules clean

obj-m += myModule.o

4.编译

root@zhangjun-virtual-machine:/home/zhangjun/zj_driver/myModule# make

make -C /usr/src/linux-headers-4.4.0-31-generic/ M=`pwd` modules

make[1]: 正在进入目录 `/usr/src/linux-headers-4.4.0-31-generic'

CC [M] /home/zhangjun/zj_driver/myModule/myModule.o

Building modules, stage 2.

MODPOST 1 modules

CC /home/zhangjun/zj_driver/myModule/myModule.mod.o

LD [M] /home/zhangjun/zj_driver/myModule/myModule.ko

make[1]:正在离开目录 `/usr/src/linux-headers-4.4.0-31-generic'

5.安装驱动

root@zhangjun-virtual-machine:/home/zhangjun/zj_driver/myModule# insmod myModule.ko

root@zhangjun-virtual-machine:/home/zhangjun/zj_driver/myModule# cat /proc/modules

myModule 16384 0 - Live 0xffffffffc03d4000 (OE)

nls_utf8 16384 1 - Live 0xffffffffc016f000

isofs 40960 1 - Live 0xffffffffc03f4000

vmw_vsock_vmci_transport 28672 1 - Live 0xffffffffc03cc000

vsock 36864 2 vmw_vsock_vmci_transport, Live 0xffffffffc0165000

bnep 20480 2 - Live 0xffffffffc0178000

rfcomm 69632 8 - Live 0xffffffffc050b000

nfsd 315392 13 - Live 0xffffffffc05e4000

auth_rpcgss 57344 1 nfsd, Live 0xffffffffc0542000

nfs_acl 16384 1 nfsd, Live 0xffffffffc038b000

nfs 249856 0 - Live 0xffffffffc05a6000

binfmt_misc 20480 1 - Live 0xffffffffc0393000

lockd 90112 2 nfsd,nfs, Live 0xffffffffc052b000

grace 16384 2 nfsd,lockd, Live 0xffffffffc0386000

sunrpc 331776 19 nfsd,auth_rpcgss,nfs_acl,nfs,lockd, Live 0xffffffffc04b9000

fscache 61440 1 nfs, Live 0xffffffffc04a9000

coretemp 16384 0 - Live 0xffffffffc03c7000

kvm_intel 167936 0 - Live 0xffffffffc057c000

kvm 532480 1 kvm_intel, Live 0xffffffffc0426000

snd_ens1371 28672 2 - Live 0xffffffffc0365000

snd_ac97_codec 131072 1 snd_ens1371, Live 0xffffffffc0405000

irqbypass 16384 1 kvm, Live 0xffffffffc0381000

crct10dif_pclmul 16384 0 - Live 0xffffffffc037c000

gameport 16384 1 snd_ens1371, Live 0xffffffffc0373000

crc32_pclmul 16384 0 - Live 0xffffffffc034b000

ac97_bus 16384 1 snd_ac97_codec, Live 0xffffffffc0400000

snd_pcm 106496 2 snd_ens1371,snd_ac97_codec, Live 0xffffffffc03d9000

aesni_intel 167936 0 - Live 0xffffffffc039d000

vmw_balloon 20480 0 - Live 0xffffffffc036d000

snd_seq_midi 16384 0 - Live 0xffffffffc0360000

snd_seq_midi_event 16384 1 snd_seq_midi, Live 0xffffffffc035b000

aes_x86_64 20480 1 aesni_intel, Live 0xffffffffc0355000

lrw 16384 1 aesni_intel, Live 0xffffffffc0321000

gf128mul 16384 1 lrw, Live 0xffffffffc0350000

snd_rawmidi 32768 2 snd_ens1371,snd_seq_midi, Live 0xffffffffc0342000

glue_helper 16384 1 aesni_intel, Live 0xffffffffc033d000

ablk_helper 16384 1 aesni_intel, Live 0xffffffffc0277000

cryptd 20480 2 aesni_intel,ablk_helper, Live 0xffffffffc031b000

joydev 20480 0 - Live 0xffffffffc0315000

input_leds 16384 0 - Live 0xffffffffc0307000

serio_raw 16384 0 - Live 0xffffffffc0233000

snd_seq 69632 2 snd_seq_midi,snd_seq_midi_event, Live 0xffffffffc032b000

snd_seq_device 16384 3 snd_seq_midi,snd_rawmidi,snd_seq, Live 0xffffffffc0326000

snd_timer 32768 2 snd_pcm,snd_seq, Live 0xffffffffc030c000

btusb 45056 0 - Live 0xffffffffc02fb000

btrtl 16384 1 btusb, Live 0xffffffffc0272000

btbcm 16384 1 btusb, Live 0xffffffffc0160000

btintel 16384 1 btusb, Live 0xffffffffc0145000

bluetooth 516096 25 bnep,rfcomm,btusb,btrtl,btbcm,btintel, Live 0xffffffffc027c000

snd 81920 11 snd_ens1371,snd_ac97_codec,snd_pcm,snd_rawmidi,snd_seq,snd_seq_device,snd_timer, Live 0xffffffffc021e000

soundcore 16384 1 snd, Live 0xffffffffc006b000

nfit 32768 0 - Live 0xffffffffc01f0000

vmwgfx 229376 3 - Live 0xffffffffc0239000

ttm 94208 1 vmwgfx, Live 0xffffffffc01d8000

drm_kms_helper 143360 1 vmwgfx, Live 0xffffffffc01fa000

drm 360448 6 vmwgfx,ttm,drm_kms_helper, Live 0xffffffffc017f000

shpchp 36864 0 - Live 0xffffffffc0156000

fb_sys_fops 16384 1 drm_kms_helper, Live 0xffffffffc0151000

syscopyarea 16384 1 drm_kms_helper, Live 0xffffffffc014c000

vmw_vmci 65536 2 vmw_vsock_vmci_transport,vmw_balloon, Live 0xffffffffc0134000

sysfillrect 16384 1 drm_kms_helper, Live 0xffffffffc00fc000

sysimgblt 16384 1 drm_kms_helper, Live 0xffffffffc00b8000

i2c_piix4 24576 0 - Live 0xffffffffc0120000

8250_fintek 16384 0 - Live 0xffffffffc00f7000

parport_pc 36864 0 - Live 0xffffffffc00ae000

ppdev 20480 0 - Live 0xffffffffc0065000

mac_hid 16384 0 - Live 0xffffffffc003d000

lp 20480 0 - Live 0xffffffffc0043000

parport 49152 3 parport_pc,ppdev,lp, Live 0xffffffffc0030000

hid_generic 16384 0 - Live 0xffffffffc004d000

usbhid 49152 0 - Live 0xffffffffc0127000

hid 118784 2 hid_generic,usbhid, Live 0xffffffffc0102000

psmouse 122880 0 - Live 0xffffffffc00d8000

mptspi 24576 2 - Live 0xffffffffc00cd000

mptscsih 40960 1 mptspi, Live 0xffffffffc00be000

mptbase 102400 2 mptspi,mptscsih, Live 0xffffffffc0072000

e1000 135168 0 - Live 0xffffffffc008c000

scsi_transport_spi 32768 1 mptspi, Live 0xffffffffc0052000

ahci 36864 1 - Live 0xffffffffc005b000

libahci 32768 1 ahci, Live 0xffffffffc0027000

pata_acpi 16384 0 - Live 0xffffffffc000f000

fjes 28672 0 - Live 0xffffffffc001f000

vmw_pvscsi 24576 0 - Live 0xffffffffc0014000

vmxnet3 57344 0 - Live 0xffffffffc0000000

安装驱动应该会调用myModule_init函数，那么应该有打印输出，但是实际上没有；

6.卸载驱动

root@zhangjun-virtual-machine:/home/zhangjun/zj_driver/myModule# rmmod myModule.ko

7.模块安装时的打印

步骤5在安装myModule.ko的时候终端上并没有打印出信息，但是实际上打印的信息写入文件/var/log/kern.log，可以通过tail命令查看该文件最后的条目。

root@zhangjun-virtual-machine:/home/zhangjun/zj_driver/myModule# tail -f /var/log/kern.log

Jan 15 11:17:16 zhangjun-virtual-machine kernel: [ 5755.442589] myModule: module verification failed: signature and/or required key missing - tainting kernel

Jan 15 11:17:16 zhangjun-virtual-machine kernel: [ 5755.448875] myModule init.

Jan 15 11:21:12 zhangjun-virtual-machine kernel: [ 5991.177018] myModule exit.

8.关于printk函数

Linux 内核中通过printk输出信息，信息的类型在文件/usr/src/ linux-headers-4.4.0-31-generic /include/linux/printk.h中(有些源码在文件include\linux\kernel.h中)定义。

* These can be used to print at the various log levels.

* All of these will print unconditionally, although note that pr_debug()

* and other debug macros are compiled out unless either DEBUG is defined

* or CONFIG_DYNAMIC_DEBUG is set.

#define pr_emerg(fmt, ...) \

printk(KERN_EMERG pr_fmt(fmt), ##__VA_ARGS__)

#define pr_alert(fmt, ...) \

printk(KERN_ALERT pr_fmt(fmt), ##__VA_ARGS__)

#define pr_crit(fmt, ...) \

printk(KERN_CRIT pr_fmt(fmt), ##__VA_ARGS__)

#define pr_err(fmt, ...) \

printk(KERN_ERR pr_fmt(fmt), ##__VA_ARGS__)

#define pr_warning(fmt, ...) \

printk(KERN_WARNING pr_fmt(fmt), ##__VA_ARGS__)

#define pr_warn pr_warning

#define pr_notice(fmt, ...) \

printk(KERN_NOTICE pr_fmt(fmt), ##__VA_ARGS__)

#define pr_info(fmt, ...) \

printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)

如果不指定，默认是 DEFAULT_MESSAGE_LOGLEVE，和KERN_WARNING一样。
root@vickytong:/usr/src/ linux-headers-4.4.0-31-generic# find . -name “*.h” | xargs grep “DEFAULT_MESSAGE_LOGLEVE”

./include/generated/autoconf.h: #define CONFIG_MESSAGE_LOGLEVEL_DEFAULT 4

9.交叉编译

有时候我们需要将模块移植到其他芯片方案的主机（或开发板）上运行，那么需要交叉编译。交叉编译需要修改Makefile，主要是修改kernel代码的路径和编译工具。kernel代码的路径要修改为目的主机系统的源代码路径，编译工具gcc要修改为目的主机芯片架构对应的编译工具。设置编译器，与编译内核用的编译器要一致。下面为编译驱动时，在terminal终端设置环境变量如下：

root@zhangjun-virtual-machine:/home/zhangjun/zj_driver/myModule# source /opt/Xilinx/SDK/2015.4/settings64.sh

root@zhangjun-virtual-machine:/home/zhangjun/zj_driver/myModule# export ARCH=arm

root@zhangjun-virtual-machine:/home/zhangjun/zj_driver/myModule# export CROSS_COMPILE=arm-xilinx-linux-gnueabi-

说明：在目前ZedBoard上跑的linux系统，使用该编译器似乎也能编译驱动插入到内核中去(后面做gpio驱动时仔细验证):

root@zhangjun-virtual-machine:/home/zhangjun/zj_driver/myModule# export ARCH=arm

root@zhangjun-virtual-machine:/home/zhangjun/zj_driver/myModule# export CROSS_COMPILE= arm-linux-gnueabihf-

makefile文件修改如下：

#kernel代码的路径

KERN_DIR = /home/zhangjun/linux

obj-m := myModule.o

all:

make -C $(KERN_DIR) ARCH=arm M=`pwd` modules

clean:

rm -rf .*.cmd *.o *.mod.c *.ko .tmp_versions

10.下载、安装和卸载

在Zedboard上的linux挂在nfs，在Terminal上做如下操作：

analog@analog:~$ sudo mount -t nfs 192.168.0.25:/home/zhangjun /mnt/

mount.nfs: /mnt is busy or already mounted

analog@analog:~$ cd /mnt

analog@analog:/mnt$ cd zj_driver

analog@analog:/mnt/zj_driver$ ls

driver_demo myModule

analog@analog:/mnt/zj_driver$ cd myModule

analog@analog:/mnt/zj_driver/myModule$ ls

Makefile Module.symvers myModule.c myModule.ko myModule.mod.o

Makefile~ modules.order myModule.c~ myModule.mod.c myModule.o

analog@analog:/mnt/zj_driver/myModule$ insmod myModule.ko

insmod: ERROR: could not insert module myModule.ko: Operation not permitted

analog@analog:/mnt/zj_driver/myModule$ sudo su

root@analog:/mnt/zj_driver/myModule# insmod myModule.ko

root@analog:/mnt/zj_driver/myModule# cat /proc/modules

myModule 737 0 - Live 0xbf000000 (O)

root@analog:/mnt/zj_driver/myModule# rmmod myModule.ko

11.添加模块参数

有时候需要从用户态传参数给内核模块，这时候在内核模块中需要通过宏module_param声明参数。本例增加两个参数，一个是字符串参数cString，一个是int型参数iInt，修改后代码如下：

#include <linux/kernel.h>

#include <linux/module.h>

#include <linux/types.h>

static char* cString = NULL;

static int iInt = 0;

module_param(cString, charp, 0644);

module_param(iInt, int, 0644);