嵌入式

arm linux下使用mdev vs udev

2019-07-12 18:52发布

站内文章 / 嵌入式Linux
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我要啦免费统计 udev 和mdev 是两个使用uevent 机制处理热插拔问题的用户空间程序，两者的实现机理不同。udev 是基于netlink 机制的，它在系统启动时运行了一个deamon 程序udevd，通过监听内核发送的uevent 来执行相应的热拔插动作，包括创建/删除设备节点，加载/卸载驱动模块等等。mdev 是基于uevent_helper 机制的，它在系统启动时修改了内核中的uevnet_helper 变量（通过写/proc/sys/kernel/hotplug），值为“/sbin/mdev”。这样内核产生uevent 时会调用uevent_helper 所指的用户级程序，也就是mdev，来执行相应的热拔插动作。udev 使用的netlink 机制在有大量uevent 的场合效率高，适合用在PC 机上；而mdev 使用的uevent_helper 机制实现简单，适合用在嵌入式系统中。另外要说明的一点是,uevent_helper 的初始值在内核编译时时可配置的，默认值为/sbin/hotplug。如果想修改它的值，写/proc/sys/kernel/hotplug 文件就可以了，例如： echo “/sbin/mdev” > /proc/sys/kernel/hotplug 补充一点：如果使用的是udevd,那么uevent_helper变量应为空，即 echo “ ” > /proc/sys/kernel/hotplug refer to
http://sxw0624.blog.163.com/blog/static/200168038201272451049893/
http://bbs.csdn.net/topics/300056887
http://blog.csdn.net/walkingman321/article/details/5917737

1.udev

1.启动方式
一般是在inittab的rcS的服务启动列表里面去启动
/etc/
root@freescale /etc/rc.d$ cat rcS #!/bin/sh # minimal startup script, will work with msh (this is best available in # MMUless format). # load the configuration information . /etc/rc.d/rc.conf //服务配置文件 mode=${1:-start} if [ $mode = "start" ] then     services=$cfg_services else     services=$cfg_services_r fi cfg_services=${2:-$services} echo "cfg:" echo $cfg_services # run the configured sequence for i in $cfg_services do     if [ -x /etc/rc.d/init.d/$i ]     then                                                                                 /etc/rc.d/init.d/$i $mode //调用各个服务     fi                                                                           done if [ $# -ge 2 ] then      exit 0 fi # show all kernel log messages #echo 8 >  /proc/sys/kernel/printk # run rc.local if present and executable if [ -x /etc/rc.d/rc.local ] then      /etc/rc.d/rc.local $mode fi
root@freescale /etc/rc.d$ cat rc.conf all_services="mount-proc-sys mdev udev hostname devfsd depmod modules filesystems syslog network inetd portmap dropbear sshd boa smb dhcpd settime fslgnome watchdog bluetooth gtk2 pango" all_services_r="pango gtk2 bluetooth watchdog fslgnome settime dhcpd smb boa sshd dropbear portmap inetd network syslog filesystems modules depmod devfsd hostname udev mdev mount-proc-sys" cfg_services="mount-proc-sys hostname depmod modules filesystems inetd " cfg_services_r=" inetd filesystems modules depmod hostname mount-proc-sys" export HOSTNAME="freescale" export NTP_SERVER="" export MODLIST="" export RAMDIRS="/tmp /var" export TMPFS="tmpfs" export TMPFS_SIZE="512k" export READONLY_FS="" export INETD_ARGS="" export BOA_ARGS="" export SMBD_ARGS="" export NMBD_ARGS="" export DHCP_ARG="" export DEPLOYMENT_STYLE="JFFS2" export SYSCFG_DHCPC_CMD="udhcpc -b -i " export DROPBEAR_ARGS=""
root@freescale /etc/rc.d/init.d$ cat udev #!/bin/sh PATH=$PATH:/sbin:/bin if [ ! -x /sbin/udevd ] then exit 0 fi case "$1" in start) echo "" > /proc/sys/kernel/hotplug mount -n -o mode=0755 -t tmpfs tmpfs /dev # Create static device nodes in /dev mknod /dev/console c 5 1 mknod /dev/null c 1 3 echo "Starting the hotplug events dispatcher udevd" udevd --daemon echo "Synthesizing initial hotplug events" udevtrigger udevsettle --timeout=300 mkdir /dev/pts mount -n -t devpts devpts /dev/pts mkdir /dev/shm ;; stop) ;; reload) udevcontrol --reload_rules ;; *) echo "Usage: /etc/rc.d/init.d/udev {start|stop|reload}" echo exit 1 ;; esac exit 0


如果不需要启动时启动，需要在rc.conf中删除掉对应的服务项目
手动启动udev：
/etc/rc.d/init.d/udev start

启动时，主要启动了
        udevd --daemon
        udevtrigger

2.mdev
busybox带一个简化版，mdev ，通过mdev -s扫描设备文件，相当于sbin/udevstart；通过echo /sbin/mdev > /proc/sys/kernel/hotplug启用自动扫描，相当于/sbin/udevd --daemon

[root@hemei]# cat /etc/init.d/rcS #! /bin/sh PATH=/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/bin: runlevel=S prevlevel=N umask 022 export PATH runlevel prevlevel # #       Trap CTRL-C &c only in this shell so we can interrupt subprocesses. # trap ":" INT QUIT TSTP /bin/hostname hemei /bin/mount -n -t proc none /proc /bin/mount -n -t sysfs none /sys /bin/mount -n -t usbfs none /proc/bus/usb /bin/mount -t ramfs none /dev
echo /sbin/mdev > /proc/sys/kernel/hotplug /sbin/mdev -s /bin/hotplug # mounting file system specified in /etc/fstab mkdir -p /dev/pts mkdir -p /dev/shm /bin/mount -n -t devpts none /dev/pts -o mode=0622 /bin/mount -n -t tmpfs tmpfs /dev/shm /bin/mount -n -t ramfs none /tmp #/bin/mount -n -t ramfs none /var mkdir -p /var/empty mkdir -p /var/log mkdir -p /var/log/boa mkdir -p /var/lock mkdir -p /var/run mkdir -p /var/tmp /sbin/hwclock -s -f /dev/rtc syslogd /sbin/ifconfig lo 127.0.0.1 ifconfig eth0 hw ether 10:23:45:67:89:ab /sbin/ifconfig eth0 192.168.1.168 /sbin/route add default gw 192.168.1.1 sbin/telnetd -l /bin/login ip link set can0 up type can bitrate 125000 export PATH=$PATH:/usr/local/mysql/bin export LD_LIBRARY_PATH=/usr/local/mysql/lib/mysql:$LD_LIBRARY_PATH export LD_PRELOAD=/usr/lib/preloadable_libiconv.so /usr/local/mysql/bin/mysqld_safe --user=root &

[root@hemei]# 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
# misc devices mmcblk0p1       0:0     0600    =sdcard */bin/hotplug sda1            0:0     0600    =udisk * /bin/hotplug
# sound card controlC[0-9]   0:0     0664    =snd/ pcmC[0-9]D[0-9][cp]     0:0     0664    =snd/ timer           0:0     0664    =snd/ seq             0:0     0664    =snd/


[root@hemei]# cat /bin/hotplug #!/bin/sh case $MDEV in sda1)         DEVNAME=udisk         MOUNTPOINT=/udisk         ;; mmcblk0p1)         DEVNAME=sdcard         MOUNTPOINT=/sdcard         ;; *)         exit 0         ;; esac
case $ACTION in remove)         /bin/umount $MOUNTPOINT || true         rmdir $MOUNTPOINT >/dev/null 2>&1 || true         ;; *)         /bin/mkdir $MOUNTPOINT > /dev/null 2>&1 || true         /bin/mount -o sync -o noatime -o nodiratime -t vfat /dev/$DEVNAME $MOUNTPOINT > /dev/null 2>&1 || true         ;; esac
exit 0 http://www.embedu.org/Column/Column167.htm
 http://blog.csdn.net/hugerat/article/details/3437099

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