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节省固件空间

对于仅有4M闪存的设备,闪存空间是稀有的。您在使用imagebuilder编译自己的固件镜像文件时,可以移除一些不会使用到的软件包来节省一些空间。如想完全移除IPv6支持和相关的软件包,您可以在imagebuilder的make命令中通过“CONFIG_IPV6=n”来实现。

作用 相关软件包
移除pppoe -ppp -ppp-mod-pppoe
移除IPv6 -ip6tables -odhcp6c -kmod-ipv6 -kmod-ip6tables -odhcpd-ipv6only
移除dhcp server -odhcpd
移除iptables -iptables
移除opkg -opkg
添加精减的LuCIuhttpd uhttpd-mod-ubus libiwinfo-lua luci-base luci-app-firewall luci-mod-admin-full luci-theme-bootstrap
添加zram¹ zram-swap

¹ 备注: 4M闪存的设备请不要使用 zram-swap,因为这会增加固件所需的闪存空间。这里之所以会列出,是因为它对于低内存设备很有用。

镜像构建命令行示例
备注: 您需要根据设备修改下方命令行中的PROFILE=tl-wr941nd-v6,使用make info命令可显示可用的设备清单。

是否集成LuCI 作用 Imagebuilder命令行
集成LuCI 移除pppoe和IPv6,包含必需的LuCI组件而非完整的LuCI软件包 make image PROFILE=tl-wr941nd-v6 \ PACKAGES=“uhttpd uhttpd-mod-ubus libiwinfo-lua luci-base luci-app-firewall luci-mod-admin-full luci-theme-bootstrap \ -ppp -ppp-mod-pppoe -ip6tables -odhcp6c -kmod-ipv6 -kmod-ip6tables -odhcpd-ipv6only”
不集成LuCI 移除pppoe和IPv6 make image PROFILE=tl-wr941nd-v6 PACKAGES=“-ppp -ppp-mod-pppoe -ip6tables -odhcp6c -kmod-ipv6 -kmod-ip6tables -odhcpd-ipv6only”

相关资源:

If the device has 16MB or less of RAM, then it should only be used as Internal AP (e.g. to extend Wi-Fi coverage).

Example image builder command line
Note: In the command line shown below, you need to adjust PROFILE=tl-wr941nd-v6 to your device. Use make info to list possibilities.

RAM Action Imagebuilder commandline
16MB - remove pppoe and IPv6
- remove all related elements to iptables
- remove dhcp servers
+ add LUCI
+ add zram-swap
- remove opkg - not needed after making these adjustments
make image PROFILE=tl-wr941nd-v6 \ PACKAGES=“uhttpd uhttpd-mod-ubus libiwinfo-lua luci-base luci-app-firewall luci-mod-admin-full luci-theme-bootstrap zram-swap \ -ppp -ppp-mod-pppoe -iptables -ip6tables -odhcp6c -kmod-ipv6 -kmod-ip6tables -odhcpd-ipv6only -odhcpd -opkg”
32MB - remove pppoe and IPv6
+ add LUCI
+ add zram-swap
- remove opkg - not needed after making these adjustments
make image PROFILE=tl-wr941nd-v6 \ PACKAGES=“uhttpd uhttpd-mod-ubus libiwinfo-lua luci-base luci-app-firewall luci-mod-admin-full luci-theme-bootstrap zram-swap \ -ppp -ppp-mod-pppoe -ip6tables -odhcp6c -kmod-ipv6 -kmod-ip6tables -odhcpd-ipv6only -opkg”

Resources:

This option compiles the kernel modules inside the kernel, you can either pick what modules you think can be integrated and make them built-in by pressing “y” on them when in the menuconfig, or do a quick-and-dirty change of the kernel config with (adjust the path in this example to point to your target's actual kernel config)

sed -i -e "s/=m/=y/g" build_dir/target-mipsel_24kc_musl/linux-ramips_mt7620/linux-4.14.63/.config

This will work only if your device's kernel partition is big enough to accomodate the slightly larger kernel, or if the device is using dynamic partitions.

This was reported by Daniel Santos in an email in the OpenWrt Devel mailing list, 30 Oct 2018 (currently the mailing list archive server is unavailable so I cannot link directly to the mail in the archive).

His comments:

I did a quick experiment of this and instead of saving 4k, my *image* is a full 256k smaller. I haven't analysed the specifics, but also this means less RAM consumed because squashfs uses the page cache for uncompressed files. Further, modules inherently have greater overhead, even after __init sections have been discarded. The only downside is that built-ins cannot be unloaded and will always occupy a portion of RAM. But having them built into the kernel is far more efficient.

(The “surprising” change in image size may be due to the block size of the squashfs image. See, for example include/image-commands.mk and include/image.mk in November, 2018 sources)

In a follow up mail by Phillip Prindeville pointed out the main drawback of this method.

Some hardware (it’s rare but not unheard of) can only be reset by unloading and reloading the module that controls it. Otherwise, you have to reboot the box. If you build all of your drivers in, then rebooting is all you have.

You can also save space by changing configuration variables using make menuconfig. In addition to the ones mentioned here you can save a tiny bit of space by disabling commands in busybox.

Options that can be disabled to save space.

Config variable Menu path Estimated savings
CONFIG_KERNEL_PRINTK Global build settings / Kernel build options / Enable support for printk
CONFIG_KERNEL_CRASHLOG Global build settings / Kernel build options / Crash logging
CONFIG_KERNEL_SWAP Global build settings / Kernel build options / Support for paging of anonymous memory (swap)
CONFIG_KERNEL_KALLSYMS Global build settings / Kernel build options / Compile the kernel with symbol table information
CONFIG_KERNEL_DEBUG_INFO Global build settings / Kernel build options / Compile the kernel with debug information
CONFIG_KERNEL_ELF_CORE Global build settings / Kernel build options / Enable process core dump support
CONFIG_IPV6 Global build settings / Enable IPv6 support in packages
CONFIG_KERNEL_MAGIC_SYSRQ Global build settings / Kernel build options / Compile the kernel with SysRq support
CONFIG_KERNEL_PRINTK_TIME Global build settings / Kernel build options / Enable printk timestamps
CONFIG_PACKAGE_MAC80211_DEBUGFS Kernel modules / Wireless Drivers / kmod-mac80211 / Export mac80211 internals in DebugFS 21 KB
CONFIG_PACKAGE_MAC80211_MESH Kernel modules / Wireless Drivers / kmod-mac80211 / Enable 802.11s mesh support 29 KB

Options that can be enabled to save space.

Config variable Menu path
CONFIG_STRIP_KERNEL_EXPORTS Global build settings / Strip unnecessary exports from the kernel image
CONFIG_USE_MKLIBS Global build settings / Strip unnecessary functions from libraries

make kernel_menuconfig options that can save space.

Config variable Menu path Comments
CONFIG_SERIAL_8250 Device Drivers / Character devices / Serial drivers / 8250/16550 and compatible serial support This will also save RAM by preventing /sbin/askfirst from running
CONFIG_EARLY_PRINTK Kernel hacking / Early printk

To build a kernel that only works with a specific device, run make kernel_menuconfig CONFIG_TARGET=subtarget to edit target/linux/<platform>/*/config-default and go to Machine selection / <Platform> machine selection and disable all devices except for the specific device. This can save some disk space and RAM.

Increase block size from the default 256 KB to improve compression. Warning: By default 3 blocks will be cached so this will also make the router use more RAM (if 3 blocks are cached, and a block size of 1024 KB is used, this will use 2,304 KB more RAM (3 * 1024 KB - 3 * 256 KB)). It may also make the router use more CPU to decompress the larger blocks.

Config variable Menu path
TARGET_SQUASHFS_BLOCK_SIZE Target Images / squashfs / Block size

Options that can be enabled to save RAM.

Config variable Menu path
PACKAGE_zram-swap Base system
PROCD_ZRAM_TMPFS Base system / procd Configuration

Reduce the number of cached blocks by running make kernel_menuconfig.

Config variable Menu path
CONFIG_SQUASHFS_FRAGMENT_CACHE_SIZE File systems / Miscellaneous filesystems / Additional option for memory-constrained systems / Number of fragments cached

The icons in LuCI are not strictly necessary and replacing them with a blank image will save about 15 KB. This bash script will take an OpenWrt git path as parameter and replace the images with a blank using the files path:

Click to display ⇲

Click to hide ⇱

#!/bin/sh
if [ -z "$1" ]; then echo Need git path as parameter; exit 1; fi
cd "$1" || exit 1
gitpath=`pwd`
echo Installing to $gitpath
mkdir -p files/www/luci-static/resources/icons/
mkdir -p files/www/luci-static/resources/cbi/
wget -O files/www/luci-static/resources/cbi/blank.gif 'https://raw.githubusercontent.com/mathiasbynens/small/master/gif-transparent.gif'
wget -O files/www/luci-static/resources/cbi/blank.png 'https://raw.githubusercontent.com/mathiasbynens/small/master/png-transparent.png'
cd feeds/luci/modules/luci-base/htdocs/luci-static/resources/cbi
for a in *.gif; do ln -s blank.gif "$gitpath"/files/www/luci-static/resources/cbi/$a; done
cd ../icons
for a in *.gif; do ln -s ../cbi/blank.gif "$gitpath"/files/www/luci-static/resources/icons/$a; done
for a in *.png; do ln -s ../cbi/blank.png "$gitpath"/files/www/luci-static/resources/icons/$a; done
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  • Last modified: 2021/10/15 08:26
  • by bobafetthotmail