自动创建设备节点：内核事件到udev/mdev机制-优快云博客

本文链接：https://blog.youkuaiyun.com/shell_albert/article/details/48157517

本文介绍了如何通过内核事件机制，结合udev或mdev自动创建设备文件。当内核抛出事件时，通过设置hotplug参数调用mdev程序，动态生成设备节点。在启动脚本中，挂载必要文件系统，如tmpfs，确保/dev为临时文件系统，避免写入Flash。然后执行echo /sbin/mdev > /proc/sys/kernel/hotplug和mdev -s命令。同时，文章展示了/etc/fstab配置和开机脚本，用于挂载分区和安装驱动模块。最后，展示了mdev配置文件/etc/mdev.conf的规则，以及加载驱动后的设备节点变化，验证了设备节点的自动创建过程。

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内核使用 event（事件）机制向外抛出消息，在应用层由udev/mdev接收到事件后，根据规则自动创建设备文件。

但是内核有事件时需要调用一个程序，以执行接下来的操作，故一般使用

echo /sbin/mdev > /proc/sys/kernel/hotplug

mdev -s

但前提是必须要挂载一些文件系统，如将/dev挂为临时文件系统，这样就不需要向Flash写数据了。

好了，先从/etc/fstab说起

/home/zhangshaoyan/ftpdir # cat /etc/fstab
proc            /proc   proc    defaults        0       0
sysfs           /sys    sysfs   defaults        0       0
/dev/mmcblk0p1 /       ext3    defaults        0       0
/dev/mmcblk0p2 /media    ext3   defaults        0       0
devpts          /dev/pts        devpts defaults        0       0
tmpfs   /var    tmpfs   defaults        0       0
tmpfs   /tmp    tmpfs   defaults        0       0
tmpfs   /dev    tmpfs   defaults        0       0

再来看看开机脚本

/home/zhangshaoyan/ftpdir # cat /etc/init.d/rcS
#!/bin/bash

#this file is used to initial local runtime environment,
#includes set environment variable,create necessary files,
#dynamic install device driver module,etc.
#July 15,2014 by shell.albert.
#Contact me with 13522296239.
#Copyright(C) 2014~2016,oristartech.com
#DO NOT CHANGE THE WHOLE SOFT-ARCHITECTURE!
#KEEP ORIGINAL DIRECTORY STRUCTURE.
#THANKS!

#mount partitions
#this will use /etc/fstab
mkdir /dev/pts -p
mount -t devpts devpts /dev/pts
mount -a

echo /sbin/mdev > /proc/sys/kernel/hotplug
mdev -s

#set environment variable
PATH=/bin:/sbin:/usr/sbin:/usr/bin:/home/zhangshaoyan/bin
export PATH
LD_LIBRARY_PATH=/lib:/home/zhangshaoyan/lib
export LD_LIBRARY_PATH

#install necessary driver module file.
HOME_DIR=/home/zhangshaoyan
DRVS_DIR=$HOME_DIR/drivers
DRVS_LIST=(\
imx5_msp430_driver.ko \
imx5_cspi_driver.ko \
imx5_led_driver.ko \
imx5_ds3234_driver.ko \
imx5_ds3650_driver.ko \
imx5_ecspi2_vnic_driver.ko \
);

#loop to install
for file_ko in ${DRVS_LIST[*]}
do

done

#create device files
#already created in /dev through static mknod command.
#mknod /dev/imx5_led1 c 1987 1
#mknod /dev/imx5_led2 c 1987 2
#mknod /dev/imx5_led3 c 1987 3
#mknod /dev/imx5_led4 c 1987 4
#mknod /dev/imx5_led5 c 1987 5
#mknod /dev/imx5_led6 c 1987 6

#mknod /dev/imx5_ds3234 c 1988 0
#mknod /dev/imx5_cspi c 1990 0
#mknod /dev/imx5_ds3650 c 1991 0

#supply by ecspi1_vnic.ko
#mknod /dev/imx5_ecspi1 c 1989 0
#mknod /dev/imx5_ecspi2 c 1992 0

#ipaddress for eth0
#fixed or dhcp
#be sure /usr/share/udhcpc/default.script file
#must exists before using dhclient.
#udhcpc
#ifconfig eth0 172.23.146.119 netmask 255.255.252.0

#ip,mac for vnic.
ifconfig zvnic0 hw ether 00:00:19:87:09:01
ifconfig zvnic0 192.168.10.53
ifconfig zvnic0

#start dropbear sshd service
mkdir -p /etc/dropbear
cd /etc/dropbear
if [ ! -f "/etc/dropbear/dropbear_rsa_host_key" ];then
        dropbearkey -t rsa -f dropbear_rsa_host_key
fi
if [ ! -f "/etc/dropbear/dropbear_dss_host_key" ];then
        dropbearkey -t dss -f dropbear_dss_host_key
fi
dropbear &

#start ftp service
tcpsvd -vE 0.0.0.0 21 ftpd -w /home/zhangshaoyan/ftpdir &

#change login directory
cd /home

#start sm
#sleep 5
#/mnt/imbsm_new/bin/zsy.sh

#the end of file,tagged by ZSY.

再来看看当mdev程序执行时，读到的配置规则文件：

/home/zhangshaoyan/ftpdir # cat /etc/mdev.conf
# system all-writable devices
full            0:0     0666
null            0:0     0666
ptmx            0:0     0666
random          0:0     0666
tty             0:0     0666
zero            0:0     0666

# console devices
tty[0-9]*       0:5     0660
vc/[0-9]*       0:5     0660

# serial port devices
s3c2410_serial0 0:5     0666    =ttySAC0
s3c2410_serial1 0:5     0666    =ttySAC1
s3c2410_serial2 0:5     0666    =ttySAC2
s3c2410_serial3 0:5     0666    =ttySAC3

# loop devices
loop[0-9]*      0:0     0660    =loop/

# i2c devices
i2c-0           0:0     0666    =i2c/0
i2c-1           0:0     0666    =i2c/1

# frame buffer devices
fb[0-9]         0:0     0666

# input devices
mice            0:0     0660    =input/
mouse.*         0:0     0660    =input/
event.*         0:0     0660    =input/
ts.*            0:0     0660    =input/

# rtc devices
rtc0            0:0     0644    >rtc
rtc[1-9]        0:0     0644

好，现在我加载驱动看看。

/home/zhangshaoyan/ftpdir # ls -l /dev/input/
total 0
crw-rw----    1 root     root       13, 64 Jan 1 00:00 event0
crw-rw----    1 root     root       13, 63 Jan 1 00:00 mice
/home/zhangshaoyan/ftpdir # insmod imx6_key_drv.ko
input: imx6_key_drv as /devices/virtual/input/input2
/home/zhangshaoyan/ftpdir # i'm running!!!!!

/home/zhangshaoyan/ftpdir # ls -l /dev/input/
total 0
crw-rw----    1 root     root       13, 64 Jan 1 00:00 event0
crw-rw----    1 root     root       13, 65 Jan 1 00:09 event1
crw-rw----    1 root     root       13, 63 Jan 1 00:00 mice
/home/zhangshaoyan/ftpdir # cat /proc/bus/input/devices
I: Bus=0000 Vendor=0000 Product=0000 Version=0000
N: Name="da9052-onkey"
P: Phys=da9052-onkey/input0
S: Sysfs=/devices/platform/imx-i2c.0/i2c-0/0-0048/da9052-onkey/input/input0
U: Uniq=
H: Handlers=kbd event0
B: EV=3
B: KEY=100000 0 0 0

I: Bus=0000 Vendor=0000 Product=0000 Version=0000
N: Name="imx6_key_drv"
P: Phys=
S: Sysfs=/devices/virtual/input/input2
U: Uniq=
H: Handlers=kbd event1
B: EV=3
B: KEY=281 0 0 0

/home/zhangshaoyan/ftpdir #