openwrt系统 sysupgrade 命令执行过程分析

0：扯淡

对这个openwrt的细节方面了解的还比较欠缺，故从实际中的经常用的功能说起，研究研究，可以了解更多的细节。

在openwrt的页面中已经涉及到下面的内容如：



其中在更新系统时候有进行配置保存及恢复的功能。

1：sysupgrade是的交互式使用命令如下：



经过上面的系统更新之后，会保存上面显示的配置文件中的内容，故更新系统不会影响配置的丢失。

3：脚本分析

脚本有点多，其中分析主要的脚本就可以了，其他的加一些打印信息可以帮助分析执行流程。

上面就是通过openwrt系统提供的sysupgrade命令来对系统进行更新的。
root@OpenWrt:~# which sysupgrade
/sbin/sysupgrade
看看脚本中的主要内容，
include /lib/upgrade

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
}
其中run_hooks函数的定义如下，其主要是执行钩子函数，即，第一个参数为：函数参数，第二个参数之后为：调用函数。

run_hooks() {
	local arg="$1"; shift
	for func in "$@"; do
		eval "$func $arg"
	done
}
	run_hooks "$CONFFILES" $sysupgrade_init_conffiles 的作用就是将需要保存的文件名字保存到"$CONFFILES"文件中，保存那些文件了
	定义在add_uci_conffiles()和add_overlayfiles()函数中。
add_uci_conffiles() {
	local file="$1"
	( find $(sed -ne '/^[[:space:]]*$/d; /^#/d; p' \
		/etc/sysupgrade.conf /lib/upgrade/keep.d/* 2>/dev/null) \
		-type f 2>/dev/null;
	  opkg list-changed-conffiles ) | sort -u > "$file"
	return 0
}

add_overlayfiles() {
	local file="$1"
	find /overlay/etc/ -type f | sed \
		-e 's,^/overlay/,/,' \
		-e '\,/META_[a-zA-Z0-9]*$,d' \
		-e '\,/functions.sh$,d' \
		-e '\,/[^/]*-opkg$,d' \
	> "$file"
	return 0
}
默认保存的文件内容如下：如果需要对自定
etc/wifidog.conf
etc/sysctl.conf
etc/squid/squid.conf
etc/shells
etc/rc.local
etc/profile
etc/passwd
etc/inittab
etc/hosts
etc/group
etc/dropbear/dropbear_rsa_host_key
etc/dropbear/dropbear_dss_host_key
etc/crontabs/root
etc/config/wifidog
etc/config/uhttpd
etc/config/system
etc/config/redirect
etc/config/network
etc/config/ip
etc/config/firewall
etc/config/dropbear
etc/config/dhcp
函数ask_bool()实现是否与命令行进行交互式的处理。
	v "Saving config files..."
	[ "$VERBOSE" -gt 1 ] && TAR_V="v" || TAR_V=""
	tar c${TAR_V}zf "$conf_tar" -T "$CONFFILES" 2>/dev/null
实现对上面的数据文件进行压缩处理，其文件名称为：/tmp/sysupgrade.tgz

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 S***E_CONFIG=1
elif ask_bool $S***E_CONFIG "Keep config files over reflash"; then
        do_save_conffiles
        export S***E_CONFIG=1
else
        export S***E_CONFIG=0
fi
上面的条件判断执行的是elif,即默认是保存更改过的配置文件。 export S***E_CONFIG=1

其中语句
kill_remaining TERM
sleep 3
kill_remaining KILL
实现对进程的term和kill操作
kill_remaining() { # [ <signal> ]
	local sig="${1:-TERM}"
	echo -n "Sending $sig to remaining processes ... "

	local stat
	for stat in /proc/[0-9]*/stat; do
		[ -f "$stat" ] || continue

		local pid name state ppid rest
		read pid name state ppid rest < $stat
		name="${name#(}"; name="${name%)}"

		local cmdline
		read cmdline < /proc/$pid/cmdline

		# Skip kernel threads 
		[ -n "$cmdline" ] || continue

		case "$name" in
			# Skip essential services
			*ash*|*init*|*watchdog*|*ssh*|*dropbear*|*telnet*|*login*|*hostapd*|*wpa_supplicant*) : ;;

			# Killable process
			*)
				if [ $pid -ne $$ ] && [ $ppid -ne $$ ]; then
					echo -n "$name "
					kill -$sig $pid 2>/dev/null
				fi
			;;
		esac
	done
	echo ""
}

在升级操作之前有一个run_ramfs()，将一个最小能运行的系统mount到内存中去。为后的操作提供运行环境。
run_ramfs() { # <command> [...]
	install_bin /bin/busybox /bin/ash /bin/sh /bin/mount /bin/umount        \
		/sbin/pivot_root /usr/bin/wget /sbin/reboot /bin/sync /bin/dd   \
		/bin/grep /bin/cp /bin/mv /bin/tar /usr/bin/md5sum "/usr/bin/[" \
		/bin/vi /bin/ls /bin/cat /usr/bin/awk /usr/bin/hexdump          \
		/bin/sleep /bin/zcat /usr/bin/bzcat /usr/bin/printf /usr/bin/wc

	install_bin /sbin/mtd
	for file in $RAMFS_COPY_BIN; do
		install_bin $file
	done
	install_file /etc/resolv.conf /lib/functions.sh /lib/functions.sh /lib/upgrade/*.sh $RAMFS_COPY_DATA

	pivot $RAM_ROOT /mnt || {
		echo "Failed to switch over to ramfs. Please reboot."
		exit 1
	}

	mount -o remount,ro /mnt
	umount -l /mnt

	grep /overlay /proc/mounts > /dev/null && {
		mount -o remount,ro /overlay
		umount -l /overlay
	}

	# spawn a new shell from ramdisk to reduce the probability of cache issues
	exec /bin/busybox ash -c "$*"
}
在整整操作之前先看看 mtd,sysupgrade 更新过程实际使用的就是mtd命令
root@OpenWrt:/overlay/etc#mtd 
Usage: mtd [<options> ...] <command> [<arguments> ...] <device>[:<device>...]

The device is in the format of mtdX (eg: mtd4) or its label.
mtd recognizes these commands:
        unlock                  unlock the device
        refresh                 refresh mtd partition
        erase                   erase all data on device
        write <imagefile>|-     write <imagefile> (use - for stdin) to device
        jffs2write <file>       append <file> to the jffs2 partition on the device
Following options are available:
        -q                      quiet mode (once: no [w] on writing,
                                           twice: no status messages)
        -n                      write without first erasing the blocks
        -r                      reboot after successful command
        -f                      force write without trx checks
        -e <device>             erase <device> before executing the command
        -d <name>               directory for jffs2write, defaults to "tmp"
        -j <name>               integrate <file> into jffs2 data when writing an image
        -p                      write beginning at partition offset

Example: To write linux.trx to mtd4 labeled as linux and reboot afterwards
         mtd -r write linux.trx linux

do_upgrade() {
	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
	[ "$S***E_CONFIG" -eq 1 -a -n "$USE_REFRESH" ] && {
		v "Refreshing partitions"
		if type 'platform_refresh_partitions' >/dev/null 2>/dev/null; then
			platform_refresh_partitions
		else
			refresh_mtd_partitions
		fi
		if type 'platform_copy_config' >/dev/null 2>/dev/null; then
			platform_copy_config
		else
			jffs2_copy_config
		fi
	}
	v "Upgrade completed"
	[ -n "$DELAY" ] && sleep "$DELAY"
	ask_bool 1 "Reboot" && {
		v "Rebooting system..."
		reboot -f
		sleep 5
		echo b 2>/dev/null >/proc/sysrq-trigger
	}
}

default_do_upgrade() {
	sync
	if [ "$S***E_CONFIG" -eq 1 -a -z "$USE_REFRESH" ]; then
		get_image "$1" | mtd -j "$CONF_TAR" write - "${PART_NAME:-image}"
	else
		get_image "$1" | mtd write - "${PART_NAME:-image}"
	fi
}

platform_do_upgrade() {
	local rootfs="$(x86_get_rootfs)"
	local rootfsdev="${rootfs##*:}"

	sync
	[ -b ${rootfsdev%[0-9]} ] && get_image "$@" | dd of=${rootfsdev%[0-9]} bs=4096 conv=fsync
	sleep 1
}

x86_get_rootfs() {
	local rootfsdev
	local rootfstype
	
	rootfstype="$(awk 'BEGIN { RS=" "; FS="="; } ($1 == "rootfstype") { print $2 }' < /proc/cmdline)"
	case "$rootfstype" in
		squashfs|jffs2)
			rootfsdev="$(awk 'BEGIN { RS=" "; FS="="; } ($1 == "block2mtd.block2mtd") { print substr($2,1,index($2, ",")-1) }' < /proc/cmdline)";;
		ext4)
			rootfsdev="$(awk 'BEGIN { RS=" "; FS="="; } ($1 == "root") { print $2 }' < /proc/cmdline)";;
	esac
		
	echo "$rootfstype:$rootfsdev"
}

jffs2_copy_config() {
	if grep rootfs_data /proc/mtd >/dev/null; then
		# squashfs+jffs2
		mtd -e rootfs_data jffs2write "$CONF_TAR" rootfs_data
	else
		# jffs2
		mtd jffs2write "$CONF_TAR" rootfs
	fi
}
refresh_mtd_partitions() {
	mtd refresh rootfs
}

其中需要注意的是不同的平台如，Atheros和x86的各个平台的执行过程有所不同，最终一点是需要将$CONF_TAR保存到系统的rootfs_data或者rootfs_data分区数据中去。