定制编译openwrt.
配置完openwrt之后，觉得实在是还不够。想装个tcpdump，结果发现没有空间了。看样子得想办法省出点空间。
仔细看了看openwrt的文件系统结构，发现openwrt是把编译出来的一份只读系统打包了，装载在/rom下，然后，修改新加的内容，单独放在另一个可读写的地方，装载在/overlay上。/rom和/overlay的文件都不是全部，两者结合，才真正形成了一个复合的文件系统，加载于/。对系统文件进行替换后，由于/rom不可写，不要的那个文件并没有真正删除，其空间也就浪费了。这在小小的路由器上，是不可接受的。因此对系统的修改，比如我重新弄了个改完BUG后的dropbear，就实在是大大的浪费。
而且/rom里的文件，实际存储是压缩了的，文件压缩自然可省空间。因此有必要编译一份openwrt。过程：
1. host安装必要的组件: apt-get install gawk flex unzip git subversion
2. 下载源代码。 svn co svn://svn.openwrt.org/openwrt 。从此trunk目录就成了build_root目录。
3. 更新feeds. ./scripts/feeds update -a
4. 安装必须的组件 ./scripts/feeds install tcpdump psmisc
5. make menuconfig，设置一些组件。使得Target System为Atheros AR71xx/AR7240/AR913x/AR934x。Target Profile为TP-LINK TL-WR841ND v7。
6. 继续设置menuconfig里的组件。完了后make defconfig检查，确保得到以下结果：
diff y kmod-ipt-nathelper-extra y kmod-mppe y kmod-pptp y pptp y uhttpd y tcpdump y psmisc m
注意psmisc用Module方式就可以了，因为里面有多个程序，我只需要最重要的pstree。
7. make
8. 修改dropbear bug。见： http://www.swigger.net/archives/291.html
cd ./build_dir/target-mips_r2_uClibc-0.9.32/dropbear-0.53.1
note @2012-01-22: this bug is fixed by dropbear.
9. 修改config.sh ./package/base-files-network/files/lib/network/config.sh
见 http://www.swigger.net/archives/316.html
- if [ -d /proc/sys/net/$fam ]; then
+ if ls /proc/sys/net/$fam/*/$ifn 2>/dev/null ; then
10. 修改package/base-files-network/files/sbin/ifdown . 见 http://www.swigger.net/archives/336.html
11. 修改 rcS
--- package/base-files/files/etc/init.d/rcS (revision 29839) +++ package/base-files/files/etc/init.d/rcS (working copy) @@ -4,15 +4,15 @@ run_scripts() { for i in /etc/rc.d/$1*; do [ -x $i ] && $i $2 2>&1 - done | $LOGGER + done } system_config() { config_get_bool foreground $1 foreground 0 } -LOGGER="cat" -[ -x /usr/bin/logger ] && LOGGER="logger -s -p 6 -t sysinit" +#LOGGER="cat" +#[ -x /usr/bin/logger ] && LOGGER="logger -s -p 6 -t sysinit" . /etc/functions.sh
12. 来到build_root目录，执行：
$ mkdir -p files/etc/config $ mkdir files/etc/ppp $ cp ./build_dir/target-mips_r2_uClibc-0.9.32/dropbear-0.53.1/ipkg-ar71xx/dropbear/etc/config/dropbear files/etc/config $ vim files/etc/config/dropbear + option GatewayPorts 1 $ cp ./build_dir/target-mips_r2_uClibc-0.9.32/pptp-1.7.1/ipkg-ar71xx/pptp/etc/ppp/options.pptp files/etc/ppp/ $ vim files/etc/ppp/options.pptp - defaultroute $ cp build_dir/target-mips_r2_uClibc-0.9.32/root-ar71xx/etc/shells files/etc/ $ vim files/etc/shells + /bin/false $ mkdir -p files/usr/bin $ cp build_dir/target-mips_r2_uClibc-0.9.32/psmisc-22.13/ipkg-ar71xx/psmisc/usr/bin/pstree files/usr/bin/ $ ./staging_dir/toolchain-mips_r2_gcc-4.5-linaro_uClibc-0.9.32/bin/mips-openwrt-linux-strip files/usr/bin/pstree $ make
13. 大功告成。使用 bin/ar71xx/openwrt-ar71xx-generic-tl-wr841nd-v7-squashfs-factory.bin 刷系统。
刷完系统再改改配置文件。(/rom/etc/config下的总是会copy到/overlay/etc/config中，预置配置文件省不了空间）组件就不用装了。
结果是嵌了tcpdump和其它我需要的几个组件，最后还剩下几百K的空间。总的来说成果很好。
root@OpenWrt:~# df Filesystem 1K-blocks Used Available Use% Mounted on /dev/root 1792 1792 0 100% /rom tmpfs 14780 84 14696 1% /tmp tmpfs 512 0 512 0% /dev /dev/mtdblock3 844 80 764 9% /overlay overlayfs:/overlay 844 80 764 9% / root@OpenWrt:~# mount rootfs on / type rootfs (rw) /dev/root on /rom type squashfs (ro,relatime) proc on /proc type proc (rw,noatime) sysfs on /sys type sysfs (rw,noatime) tmpfs on /tmp type tmpfs (rw,nosuid,nodev,noatime,size=14780k) tmpfs on /dev type tmpfs (rw,noatime,size=512k,mode=755) devpts on /dev/pts type devpts (rw,noatime,mode=600) /dev/mtdblock3 on /overlay type jffs2 (rw,noatime) overlayfs:/overlay on / type overlayfs (rw,noatime) debugfs on /sys/kernel/debug type debugfs (rw,relatime)
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Carefully looked at the openwrt file system structure, that openwrt is to build out a read-only system, packaged, and loaded in the / rom, and then modify the new additional content can be read separately in another place, mounted on / overlay on. / rom and / overlay file is not full, a combination of both, really form a complex file system, load on /. Replace the system files, due to / rom can not write, do not that does not really delete the file, its also a waste of space. This little router is unacceptable. Therefore, the system changes, such as I re-broke a complete change BUG after dropbear, it really is a big waste.Anyway, thanks for sharing.
Replace the system files, due to / rom can not write, do not that does not really delete the file, its also a waste of space. This little router is unacceptable. Therefore, the system changes, such as I re-broke a complete change BUG after dropbear, it really is a big waste.Anyway, thanks for sharing.