热插拔机制

热插拔：hotplug / uevent 机制

//一下内容来自为东山  二期  28课

class_device_create
         class_device_register
class_device_add
kobject_uevent(&class_dev->kobj, KOBJ_ADD);
kobject_uevent_env(kobj, action, NULL);


// action_string = "add";
action_string = action_to_string(action);


/* 分配保存环境变量的内存 */
/* environment values */
buffer = kmalloc(BUFFER_SIZE, GFP_KERNEL);

/* 设置环境变量 */
envp [i++] = scratch;
scratch += sprintf(scratch, "ACTION=%s", action_string) + 1;
envp [i++] = scratch;
scratch += sprintf (scratch, "DEVPATH=%s", devpath) + 1;
envp [i++] = scratch;
scratch += sprintf(scratch, "SUBSYSTEM=%s", subsystem) + 1;

/* 调用应用程序: 比如mdev */
/* 启动脚本 echo /sbin/mdev > /proc/sys/kernel/hotplug 
* 设置了uevent_helper为“/sbin/mdev“
*/

argv [0] = uevent_helper;  // = "/sbin/mdev"
argv [1] = (char *)subsystem;
argv [2] = NULL;
call_usermodehelper (argv[0], argv, envp, 0);

call_usermodehelper ：内核中直接运行用户空间程序

分析: busybox mdev.c  


100ask: uevent_helper = /sbin/mdev
envp[0] = HOME=/
envp[1] = PATH=/sbin:/bin:/usr/sbin:/usr/bin
envp[2] = ACTION=add
envp[3] = DEVPATH=/class/sixth_drv/buttons
envp[4] = SUBSYSTEM=sixth_drv
envp[5] = SEQNUM=720
envp[6] = MAJOR=252
envp[7] = MINOR=0


mdev_main
temp = /sys/class/sixth_drv/buttons
make_device(temp, 0);
/* 确定设备文件名,类型,主次设备号 */
device_name = bb_basename(path);  = "buttons"


'c' == > 字符设备节点
根据"/sys/class/sixth_drv/buttons/dev"的内容确定主次设备号

mknod(device_name, mode | type, makedev(major, minor)


我接上U盘，想自动挂载，怎么办？
mdev.conf的格式：
<device regex> <uid>:<gid> <octal permissions> [<@|$|*> <command>]


device regex：正则表达式，表示哪一个设备
uid: owner
gid: 组ID
octal permissions：以八进制表示的属性
@：创建设备节点之后执行命令
$：删除设备节点之前执行命令
*: 创建设备节点之后 和 删除设备节点之前 执行命令
command：要执行的命令


写mdev.conf
1.
leds 0:0 777
led1 0:0 777
led2 0:0 777
led3 0:0 777


2.
leds?[123]? 0:0 777


3.
leds?[123]? 0:0 777 @ echo create /dev/$MDEV > /dev/console


4.
leds?[123]? 0:0 777 * if [ $ACTION = "add" ]; then echo create /dev/$MDEV > /dev/console; else echo remove /dev/$MDEV > /dev/console; fi


5. 
leds?[123]? 0:0 777 * /bin/add_remove_led.sh


把命令写入一个脚本：
add_remove_led.sh


#!/bin/sh
if [ $ACTION = "add" ]; 
then 
echo create /dev/$MDEV > /dev/console; 
else 
echo remove /dev/$MDEV > /dev/console; 
fi


6. U盘自动加载
sda[1-9]+ 0:0 777 * if [ $ACTION = "add" ]; then mount /dev/$MDEV /mnt; else umount /mnt; fi


7.
sda[1-9]+ 0:0 777 * /bin/add_remove_udisk.sh


add_remove_udisk.sh
#!/bin/sh
if [ $ACTION = "add" ]; 
then 
mount /dev/$MDEV /mnt; 
else 
umount /mnt; 
fi