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转载至CSDN；Breathomn
udevmonitor 的原理也是捕捉 netlink 的 socket 消息，这个消息是内核发出的，打印出来的消息跟我上面的小程序一样，2.6内核支持udev，udev是在用户空间实现的程序，在终端输入 udevmonitor（有的版本或许是 udevadm -monitor） 然后插拔 USB 设备，可以看到提示信息。
转载至CSDN；erigido
无论如何都需要有一个线程来监控设备的状态。比如，插槽上或下位产生的中断，这个型号可以通过很多方式，如netlink、内存映射、软中断等等方式，让用户态线程能够感知是否有USB设备上线，如果有则调用mount函数，否则的话umonut。
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/
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 $MOUNTPOINT > /dev/null 2>&1 || true ;; esac
exit 0 http://www.embedu.org/Column/Column167.htm
http://blog.csdn.net/hugerat/article/details/3437099
arm linux下使用mdev vs udev
作者：songqqnew
udev 和mdev 是两个使用uevent 机制处理热插拔问题的用户空间程序，两者的实现机理不同。udev 是基于netlink 机制的，它在系统启动时运行了一个deamon 程序udevd，通过监听内核发送的uevent 来执行相应的热拔插动作，包括创建/删除设备节点，加载/卸载驱动模块等等。mdev 是基于uevent_helper 机制的，它在系统启动时修改了内核中的uevnet_helper 变量（通过写/proc/sys/kernel/hotplug），值为“/sbin/mdev”。这样内核产生uevent
时会调用uevent_helper 所指的用户级程序，也就是mdev，来执行相应的热拔插动作。udev 使用的netlink 机制在有大量uevent 的场合效率高，适合用在PC 机上；而mdev 使用的uevent_helper 机制实现简单，适合用在嵌入式系统中。另外要说明的一点是,uevent_helper 的初始值在内核编译时时可配置的，默认值为/sbin/hotplug。如果想修改它的值，写/proc/sys/kernel/hotplug 文件就可以了，例如：
echo “/sbin/mdev” > /proc/sys/kernel/hotplug
补充一点：如果使用的是udevd,那么uevent_helper变量应为空，即
echo “ ” > /proc/sys/kernel/hotplug
refer tohttp://sxw0624.blog.163.com/blog/static/200168038201272451049893/
http://bbs.csdn.net/topics/300056887
http://blog.csdn.net/walkingman321/article/details/5917737
1.udev
1.启动方式
一般是在inittab的rcS的服务启动列表里面去启动
/etc/
root@freescale /etc/rc.d$ 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