Configuring kexec

I have a working kexeced system on a TP-Link TL-WR741ND. After making the USB mod, and additional experimenting, I ended up with a working kexeced system.

1. Download sources:

   svn checkout svn://svn.openwrt.org/openwrt/branches/backfire

2. Change directory to bildroot, then update & install feeds:

   cd backfire && ./scripts/feeds update && ./scripts/feeds install -a

3. Create defconfig and enter MenuConfig:

   make V=s defconfig && make menuconfig

   1. Select the following:
      1. Target System → Atheros AR71xx/AR7240/AR913x
      2. Target Profile → TP-LINK TL-WR741ND v1
      3. Target Images → ramdisk → Compression → lzma
      4. Target Images → tar.gz
         
         
      5. Kernel modules → Filesystems →
         1. kmod-fs-ext2
         2. kmod-fs-ext3
            
            
      6. Kernel modules → USB Support → kmod-usb-core
         1. kmod-usb-ohci
         2. kmod-usb-storage
            
            
      7. Utilities → kexec tools → Configuration → (mips) Target name for kexec kernel
         
         
   2. Exit from menu and save configuration
      
      

4. make V=s

5. Modify:
   1. ./build_dir/linux-ar71xx/linux-2.6.32.27/arch/mips/kernel/machine_kexec.c
      1. Change Line 55 to: kexec_start_address = (unsigned long) phys_to_virt(image→start);
         
         
   2. ./build_dir/toolchain-mips_r2_gcc-4.3.3+cs_uClibc-0.9.30.1/linux-2.6.32.27/arch/mips/kernel/machine_kexec.c
      1. Change Line 55 to: kexec_start_address = (unsigned long) phys_to_virt(image→start);
         
         
   3. For USB support:
      1. ./target/linux/ar71xx/files/arch/mips/ar71xx/Kconfig
         1. Add new line 176 (under config AR71XX_MACH_TL_WR741ND): select AR71XX_DEV_USB
            
            
      2. ./target/linux/ar71xx/files/arch/mips/ar71xx/mach-tl-wr741nd.c
         1. Add Line 22 (under includes): #include “dev-usb.h”
         2. Add line 102 (under static void __init tl_wr741nd_setup(void)): ar71xx_add_device_usb();
            
            

6. make kernel_menuconfig

   1. Select the following:
      1. Kernel type → Kexec system call
         
         
      2. General setup → Support initial ramdisks compressed using LZMA
         1. Built-in initramfs compression mode → LZMA
            
            
      3. Device Drivers → SCSI device support → M SCSI device support
         1. M SCSI disk support
         2. Probe all LUNs on each SCSI device
            
            
      4. Device Drivers → USB support → M Support for Host-side USB
         1. M OHCI HCD support → USB OHCI support for Atheros AR71xx
            1. M USB Mass Storage support
            2. USB announce new devices
               
               
      5. Kernel hacking → Default kernel command string → rootfstype=ext2 noinitrd console=ttyS0,115200 board=TL-WR741ND
         
         
7. Modify: ./package/base-files/files/etc/preinit
   1. Below . /etc/diag.sh, add line: rootfs=/dev/sda1
      
      
   2. Optionally you can modify: ./target/linux/generic-2.6/base-files/init
      1. Change line 50 to: mount $rootfs /mnt -o noatime
         • Blocks wear out faster if written to every time a file is accessed
           
           

8. make clean && make V=s

9. Repeat Step 5
   • Clean operation creates issues, however it's necessary for the USB patch to work
     
     

10. make V=s

11. Partition external storage, then format first partition as ext2
    
    
12. Extract contents of ./bin/ar71xx/openwrt-ar71xx-rootfs.tar.gz to root of file system
    
    
13. Copy ./bin/ar71xx/openwrt-ar71xx-vmlinux-initramfs.elf to root of file system

(to be continued)