A good all-round advice would be to start by looking at recent commits about adding a new device, to see what files where changed and how. Many files try to be as self-explanatory as possible, most of the times just opening them will be enough to understand their function.
A good method is learn by example, so you can do:
grep -lri mt300a target/
The result is minimal list of files required to add a new board:
target/linux/ramips/base-files/etc/board.d/01_leds target/linux/ramips/base-files/etc/board.d/02_network target/linux/ramips/base-files/lib/upgrade/platform.sh target/linux/ramips/base-files/lib/ramips.sh target/linux/ramips/dts/GL-MT300A.dts target/linux/ramips/image/mt7620.mk
Browse the source filtered by "add support for" and checkout the diff for newly added device
This is a general map of where most important files are located:
This folder contains files and folders that will be integrated in the firmware’s /etc folder.
These are its subfolders and files:
Note that some of these functions are now done in the DTS for the board.
This folder contains files and folders that will be integrated in the firmware’s /lib folder.
These are its subfolders and files:
This folder contains files and folders that will be integrated in the firmware’s /sbin folder, usually common <arch_name> sbin scripts and tools.
Device tree source files, or dts for short.
Certain architectures have the DTS directory deeper down. ARM devices, for example, typically have it located at files-X.yy/arch/arm/boot/dts/
If the DTS or DTSI file is already present in upstream Linux, they will usually not be present in the OpenWrt source. Configuring for the target and running make target/linux/{clean,prepare} will download and patch Linux, allowing the resulting file to be found in the build_dir
Configuration needed to build device-specific flashable images.
Board-specific configuration.
Arch-specific kernel module config file for menuconfig
After edit the files above, you need to touch the makefiles
touch target/linux/*/Makefile
The patches-* subdirectories contain the kernel patches applied for every target.
All patches should be named ‘NNN-lowercase_shortname.patch‘ and sorted into the following categories:
0xx - upstream backports
1xx - code awaiting upstream merge
2xx - kernel build / config / header patches
3xx - architecture specific patches
4xx - mtd related patches (subsystem and drivers)
5xx - filesystem related patches
6xx - generic network patches
7xx - network / phy driver patches
8xx - other drivers
9xx - uncategorized other patches
All patches must be written in a way that they are potentially upstreamable, meaning:
Test firmware images without writing them to flash by using ramdisk images.
In make menuconfig select Target Images and then you can select the ramdisk option.
This will create an image with kernel + initramfs, that will have initramfs in the name. The resulting image can be loaded in the device through the bootloader‘s tftp function and should boot to a prompt without relying on flash/filesystem support.
In order to collect relevant data for a port of OpenWrt to the device of interest one wants shell access. Most devices though do not offer a way to get a shell with telnet or ssh.
Some router offers ping test or NTP server configuration and may not properly sanitize user input. Try to enter shell script and see if you are lucky. You may need some javascript knowledges to disable client-side input validation.
$( /bin/busybox telnetd -l/bin/sh -p23 & )
$( cp /etc/shadow /www )
$( cp /etc/passwd /www )
Then try to download them to your computer and crack the hash
Some router may try to download a firmware file (e.g. TP-Link Archer C2 AC750) from specific private IP at the beginning of booting, which allow user to downgrade to older firmware
Serial access may allow you to enter console mode of u-boot for flashing/loading other firmware. Usually soldering is required. See Generic flashing over the Serial port
Some routers may be running outdated/insecure HTTP server and may be vulnerable to buffer overflow or other attack
With netgear-telnetenable many Netgear devices can be opened up for telnet access. Also see GitHub: insanid/NetgearTelnetEnable. When such means cannot be used, one could try to flash an image build from the sources published by the vendor with telnetd enabled.
With nmrpflash many Netgear devices can be flashed. Devices that are compatible with this tool become effectively unbrickable.
On WikiDevi lots of information can be found, e.g. the FCC ID is very useful when searching for documentation, datasheets and internal photo‘s (to be able to distinguish used chips without having to open the casing).
Typically one can use the following commands:
dmesg # log buffer might be to small, see note 1.
cat /proc/cmdline
cat /proc/cpuinfo
cat /proc/meminfo
cat /proc/devices
ls /sys/devices/platform
cat /proc/mtd
cat /sys/class/mtd/mtd*/offset # Linux 4.1 and newer, see note 2.
ifconfig -a
ls /sys/class/net
brctl show
cat /sys/kernel/debug/gpio # GPIO information
Note 1: Often the log buffer is to small and the earliest messages may be missing from the information retrieved with dmesg. If one build a stock image from the sources the vendor has published, a larger buffer size can be set within the kernel config.
Note 2: http://lxr.free-electrons.com/source/Documentation/ABI/testing/sysfs-class-mtd
Another useful tool for getting information for setting LEDs might be gpiodump, a MT7620 GPIOMODE register dumper (RAMIPS).
Because of the limited space, common file transfer utilities such as rsync/curl/ssh/scp/ftp/http/tftp may not be available, a stripped down version/applet may be available from busybox.
Assume the router ip is 192.168.0.123, and the file to be transfer located at /tmp/important-data.txt.
If the web interface are served from /www.
mount -o bind /tmp /www
wget http://192.168.0.123/important-data.txt
Setup an FTP server. Add an anonymous account with write permission
python -m pyftpdlib -w -p 21
busybox ftpput 192.168.0.123 important-data.txt /tmp/important-data.txt
busybox nc -l -p 12345 > important-data.txt
cat /tmp/important-data.txt | busybox nc 192.168.0.123:12345
Setup a tftp server
busybox tftp -p -l /tmp/important-data.txt -r important-data.txt 192.168.0.123
If all of the above tools/applets are unavailable, you may copy from telnet terminal but it may not work for binary file
原文：https://www.cnblogs.com/sudochen/p/12030212.html