OpenWrt sysupgrade 升级原理

OpenWrt的升级是使用sysupgrade工具来升级的，该工具为/sbin/sysupgrade脚本，可以附带很多参数，但是我们一般就直接使用命令sysupgrade openwrt-ramips-mt7621-device-squashfs-sysupgrade.bin升级

参数

说明

-i

开启交互模式

-d

重启前延迟，延迟秒数是传进来的

-v

会打印sysupgrade脚本中的一些信息，脚本中默认打印

-q

与-v相反

-n

升级后不保存配置，默认保存配置

-c

保存所有的改动配置文件到/etc/

-b

用sysupgrade.conf中指定的文件，创建.tar.gz格式备份文件

-r

用上步创建的.tar.gz文件，恢复配置

-l

列出将会备份的文件列表

-f

从.tar.gz恢复配置

-F

即使升级文件检测失败，也要升级，这个参数是危险的，慎用

-T

验证升级文件和.tar.gz配置文件，但不升级

-h

打印帮助信息

脚本分析

sysupgrade的升级流程查看/sbin/sysupgrade脚本

  1. check校验固件合法性 sysupgrade的第一步就是校验固件合法性，如下判断platform_check_image函数存在则开始执行。

    type platform_check_image >/dev/null 2>/dev/null || {
	echo "Firmware upgrade is not implemented for this platform."
	exit 1
}

for check in $sysupgrade_image_check; do
        ( eval "$check \"\$1\"" ) || {             
                echo "Image check '$check' $1 failed."
                return 1
        }                         
done

    该函数位于lib/upgrade/platform.sh中，根据产品的型号来判断各自的magic值。

    platform_check_image() {
	local board=$(ramips_board_name)
	local magic="$(get_magic_long "$1")"

	[ "$#" -gt 1 ] && return 1

	case "$board" in

	br-6475nd)
		[ "$magic" != "43535953" ] && {
			echo "Invalid image type."
			return 1
		}
		return 0
		;;
	ubnt-erx)
		nand_do_platform_check "$board" "$1"
		return $?;
		;;
	mt7621-*)
		[ "$magic" != "d00dfeed" ] && {
			echo "Invalid image type."
			return 1
		}
		return 0;
		;;
	esac

	echo "Sysupgrade is not yet supported on $board."
	return 1
}

    我们一般会在该check函数下面添加私有的校验方式，如固件的验签等功能。

  2. 保存config配置文件

    export SAVE_CONFIG=1

    默认的SAVE_CONFIG标志为为1，所以默认要保存uci配置文件

    if [ -n "$CONF_IMAGE" ]; then
	case "$(get_magic_word $CONF_IMAGE cat)" in
		# .gz files
		1f8b) ;;
		*)
			echo "Invalid config file. Please use only .tar.gz files"
			exit 1
		;;
	esac
	get_image "$CONF_IMAGE" "cat" > "$CONF_TAR"
	export SAVE_CONFIG=1
elif ask_bool $SAVE_CONFIG "Keep config files over reflash"; then
	[ $TEST -eq 1 ] || do_save_conffiles
	export SAVE_CONFIG=1
else
	export SAVE_CONFIG=0
fi

    保存config文件函数如下：

    do_save_conffiles() {
	local conf_tar="${1:-$CONF_TAR}"

	[ -z "$(rootfs_type)" ] && {
		echo "Cannot save config while running from ramdisk."
		ask_bool 0 "Abort" && exit
		return 0
	}
	run_hooks "$CONFFILES" $sysupgrade_init_conffiles
	ask_bool 0 "Edit config file list" && vi "$CONFFILES"

	v "Saving config files..."
	[ "$VERBOSE" -gt 1 ] && TAR_V="v" || TAR_V=""
	tar c${TAR_V}zf "$conf_tar" -T "$CONFFILES" 2>/dev/null

	rm -f "$CONFFILES"
}

    如果sysupgrade的时候带参数-n，sysupgrade -n openwrt-ramips-mt7621-device-squashfs-sysupgrade. bin，则会将SAVE_CONFIG=0

  3. run_hooks “” $sysupgrade_pre_upgrade

    这句的意思是：运行函数sysupgrade_pre_upgrade。先介绍下run_hooks函数，定义在文件common.sh中。

    run_hooks() {
    localarg="$1"; shift
    forfunc in "$@"; do
    eval"$func $arg"
    done
}

    run_hooks函数是钩子函数，其中传过来的第一个参数是函数运行的参数，其余参数为要运行的函数。

    disable_watchdog() {
    killall watchdog
    ( ps | grep -v 'grep' | grep '/dev/watchdog' ) && {
        echo 'Could not disable watchdog'
        return 1
    }   
}

append sysupgrade_pre_upgrade disable_watchdog

    就是在升级前，去清除watchdog进程

  4. ubus call system upgrade

    调用注册到ubus进程的system路径下的update方法，update方法设置了upgrade_running变量值为1，使得在ubus上注册的服务退出时无需等待。

    root@zihome:/usr/sbin# ubus list system -v
'system' @3b46ff0c
        "board":{}
        "info":{}
        "upgrade":{}
        "watchdog":{"frequency":"Integer","timeout":"Integer","stop":"Boolean"}
        "signal":{"pid":"Integer","signum":"Integer"}
        "nandupgrade":{"path":"String"}

  5. do_upgrade升级

    if [ -n "$(rootfs_type)" ]; then              
    v "Switching to ramdisk..."                     
    (run_ramfs '. /lib/functions.sh; include /lib/upgrade; do_upgrade') &
else                                      
    (do_upgrade) &                     
fi

    vim /lib/upgrade/common.sh

    do_upgrade() {                                                    
    clear_caches
    v "Performing system upgrade..."
    if type 'platform_do_upgrade' >/dev/null 2>/dev/null; then
            platform_do_upgrade "$ARGV"
    else
            default_do_upgrade "$ARGV"
    fi
}

    image升级，保存到对应的mtd分区，这边的PART_NAME在头部会定义为fireware

    default_do_upgrade() {
    sync
    if [ "$SAVE_CONFIG" -eq 1 ]; then
        get_image "$1" "$2" | mtd $MTD_CONFIG_ARGS -j "$CONF_TAR" write - "${PART_NAME:-image}"
    else
        get_image "$1" "$2" | mtd write - "${PART_NAME:-image}"
    fi  
}

  6. config保存/删除

    保存完固件之后，就开始处理config配置文件

    if [ "$SAVE_CONFIG" -eq 1 ] && type 'platform_copy_config' >/dev/null 2>/dev/null; then
        platform_copy_config
fi

if [ "$SAVE_CONFIG" -eq 0 ] && type 'platform_remove_config' >/dev/null 2>/dev/null; then
        platform_remove_config
fi

    如果需要保存配置文件，则将config拷贝到/overlay下，`这边的$CONF_TAR压缩包就是上面第二步保存的配置文件

    platform_copy_config() {
    local board_flash=$(mtk_board_flash)

    case "$board_flash" in
    "nand"|"spi")
            upgrade_log "Save config"
            rm -rf $1/*
            cp -af "$CONF_TAR" $1/
            sync
            ;;
    esac
}

    如果不需要保存则删除/overlay下的config

    platform_remove_config() {
    local board_flash=$(mtk_board_flash)

    case "$board_flash" in
    "nand"|"spi")
            upgrade_log "Drop config"
            rm -rf $1/*
            ;;
    esac
}

  7. 重启

    v "Upgrade completed"
                              
[ -n "$DELAY" ] && sleep "$DELAY" 
v "Rebooting system..."          
upgrade_log_end                  
reboot -f                        
sleep 2                          
force_reboot