OpenWRT按键

当按键时，则触发button_hotplug_event函数（gpio-button-hotplug.c）：调用button_hotplug_create_event产生uevent事件，调用button_hotplug_fill_even填充事件(JSON格式)，并最终调用button_hotplug_work发出uevent广播

上述广播，被procd进程中的hotplug_handler (procd/plug/hotplug.c) 收到，并根据etc/hotplug.json中预先定义的JSON内容匹配条件，定位到对应的执行函数，具体为：

[ "if",

[ "and",

[ "has", "BUTTON" ],

[ "eq", "SUBSYSTEM", "button" ],

],

[ "exec", "/etc/rc.button/%BUTTON%" ]

],

和

[ "if",

[ "eq", "SUBSYSTEM",

[ "net", "input", "usb", "ieee1394", "block", "atm", "zaptel", "tty", "button" ]

],

[ "exec", "/sbin/hotplug-call", "%SUBSYSTEM%" ]

],