安全模式作用:
只加载基本的文件系统,可以修改密码,网络配置等,可以进行升级系统,Uboot等操作;
依赖hotplug机制;
procd中进行preinit初始化;同时注册hotplug 事件;
文件/etc/hotplug-preinit.json
[ [ "case", "ACTION", { "add": [ [ "if", [ "has", "FIRMWARE" ], [ [ "exec", "/sbin/hotplug-call", "%SUBSYSTEM%" ], [ "load-firmware", "/lib/firmware" ], [ "return" ] ] ], ], }, ], [ "if", [ "and", [ "eq", "SUBSYSTEM", "button" ], ], [ "exec", "/etc/rc.button/failsafe" ] ], ]
即[ "exec", "/etc/rc.button/failsafe" ],检测到按键运行此脚本
#!/bin/sh [ "${TYPE}" = "switch" ] || echo ${BUTTON} > /tmp/failsafe_button return 0
只要按键引脚有状态变化,即创建/tmp/failsafe_button 文件,将被脚本/lib/preinit/30_failsafe_wait用到
failsafe_wait() { FAILSAFE= grep -q 'failsafe=' /proc/cmdline && FAILSAFE=true && export FAILSAFE if [ "$FAILSAFE" != "true" ]; then pi_failsafe_net_message=true preinit_net_echo "Please press button now to enter failsafe" pi_failsafe_net_message=false <span style="color:#CC0000;">fs_wait_for_key</span> f 'to enter failsafe mode' $fs_failsafe_wait_timeout && FAILSAFE=true <span style="color:#FF6600;">[ -f "/tmp/failsafe_button" ]</span> && FAILSAFE=true && echo "- failsafe button "`cat /tmp/failsafe_button`" was pressed -" [ "$FAILSAFE" = "true" ] && export FAILSAFE && touch /tmp/failsafe fi } boot_hook_add preinit_main failsafe_wait
fs_wait_for_key 函数处理按键 ' f ' 消息以及设定调试信息输出等级,此方式是通过系统调试串口进行;
[ -f "/tmp/failsafe_button" ] && FAILSAFE=true &&echo "- failsafe button "`cat /tmp/failsafe_button`" was pressed -"
此处 判断failsafe_button文件存在,即进入安全模式;
需要注意的是:procd 捕获按键信息,然后调用hotplug脚本,是在preinit阶段,此时overlay文件系统还未加载,使用的romfs,因此如果想禁用安全模式,不能在系统启动完后修改/etc/rc.button/failsafe脚本。因此preinit阶段,使用的romfs,用户修改的文件在overlayfs中,还未被加载;
So,禁用按键进入安全模式的方法是:在sysupgrade.bin固件编译阶段,修改/etc/rc.button/failsafe脚本,不创建/tmp/failsafe_button 文件即可;
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