In part 1 Debian Buster was installed on the Western Digital My Cloud Home. Unfortunately the default Kernel lacks quite a bit of features. Compiling our own kernel is desirable. Before we getting started to compile away, some base understanding of the device's boot process is required.
Boot considerations
When booting into Rescue mode (pressing the Reset button on Power-up) the system seems to look for the following files on an external USB stick:
- bluecore.audio (some sort of firmware for the RTD1295)
- sata.uImage (Kernel)
- rescue.sata.dtb (Kernel device tree)
- rescue.root.sata.cpio.gz_pad.img (Root-fs - padded to 4096kBytes)
The original software runs Android. That's the reason why you'll find 24+ partitions on the harddisk:
parted -l Model: ATA WDC WD80EFAX-68L (scsi) Disk /dev/sataa: 8002GB Sector size (logical/physical): 512B/4096B Partition Table: gpt Disk Flags: Number Start End Size File system Name Flags 1 34s 2047s 2014s FW_TABLE msftdata 2 2048s 67583s 65536s KERNEL_A msftdata 3 67584s 133119s 65536s ROOTFS_A msftdata 4 133120s 198655s 65536s ROOTFS_B msftdata 5 198656s 200703s 2048s FDT_A msftdata 6 200704s 202751s 2048s FDT_B msftdata 7 202752s 210943s 8192s AFW_A msftdata 8 210944s 276479s 65536s KERNEL_B msftdata 9 276480s 342015s 65536s ROOTFS_GOLD msftdata 10 342016s 344063s 2048s FDT_GOLD msftdata 11 344064s 352255s 8192s AFW_B msftdata 12 352256s 354303s 2048s BOOTCODE32 msftdata 13 354304s 356351s 2048s BOOTCODE64 msftdata 14 356352s 358399s 2048s BL31 msftdata 15 358400s 360447s 2048s BL32 msftdata 16 360448s 425983s 65536s KERNEL_GOLD msftdata 17 425984s 434175s 8192s AFW_GOLD msftdata 18 434176s 499711s 65536s fat32 CONFIG msftdata 19 499712s 2138111s 1638400s ext4 SYSTEM_A msftdata 20 2138112s 3776511s 1638400s ext4 SYSTEM_B msftdata 21 3776512s 5414911s 1638400s ext4 CACHE msftdata 22 5414912s 9609215s 4194304s ext4 DATA msftdata 23 9609216s 13803519s 4194304s linux-swap(v1) SWAP msftdata 24 13803520s 15628053163s 15614249644s ext4 DISKVOLUME1 msftdataIf you ran the original install from the Russian site, your bootConfig on partition 18 looks something like this:
2:B:2:;
The first column is the BOOT_STATE, the second the A or B
type partitions, and the last is the number of boot attempts. Further
reading on this can be done in the bootloader (cmd_boot.c) source code
supplied by Western Digital. Since the install leaves most partitions
untouched, setting the first to 5 would probably perform a factory reset
if you ever wanted to go back (haven't tried that!!!)
For anything permanent we should therefore choose the B marked partitions, also occasionally refernced as Rescue.
The
first partition is somewhat special as it contains information for the
bootloader from which sector to load firmware, kernel, and dtb. I
believe uBoot would be able to operate on files in partitions, which
would've been more hacker-friendly - in this case we have to supply a
valid firmware table (map). To make matters worse there is some checksum
over each referenced partition included in the map data. Hence every
time a modification to a partition is made the FW_TABLE needs updating.
Besides using the obscure Russian fwtutil-1d it is probably wiser to use Silvio Gissi's fwtablectl. Here the first partition is decoded as follows:
Firmware 1: GoldKernel RO:true Compressed:false Version: 0 Size: 12727296 (12727296 with padding) Disk Offset: 184549376 (sector 360448) Load Address: 0x03000000 Checksum: 0x4b610726 Firmware 2: GoldRescueDeviceTree RO:true Compressed:false Version: 0 Size: 61199 (61440 with padding) Disk Offset: 175112192 (sector 342016) Load Address: 0x01f00000 Checksum: 0x001eb5dc Firmware 3: GoldRescueRootfs RO:true Compressed:false Version: 0 Size: 12582912 (12582912 with padding) Disk Offset: 141557760 (sector 276480) Load Address: 0x02200000 Checksum: 0x3fff93a7 Firmware 4: GoldAudio RO:true Compressed:false Version: 0 Size: 3243056 (3243520 with padding) Disk Offset: 218103808 (sector 425984) Load Address: 0x01b00000 Checksum: 0x0dd71a22 Firmware 5: uBoot RO:true Compressed:false Version: 0 Size: 0 (0 with padding) Disk Offset: 181403648 (sector 354304) Load Address: 0x00000000 Checksum: 0x00000000 Firmware 6: Kernel RO:true Compressed:false Version: 0 Size: 12710400 (12710400 with padding) Disk Offset: 1048576 (sector 2048) Load Address: 0x03000000 Checksum: 0x4b571cf5 Firmware 7: RescueDeviceTree RO:true Compressed:false Version: 0 Size: 62778 (62976 with padding) Disk Offset: 102760448 (sector 200704) Load Address: 0x01f00000 Checksum: 0x001ff85e Firmware 8: KernelDeviceTree RO:true Compressed:false Version: 0 Size: 62778 (62976 with padding) Disk Offset: 101711872 (sector 198656) Load Address: 0x01f00000 Checksum: 0x001ff85e Firmware 9: RescueRootFS RO:true Compressed:false Version: 0 Size: 4194304 (4194304 with padding) Disk Offset: 68157440 (sector 133120) Load Address: 0x02200000 Checksum: 0x0df89573 Firmware 10: KernelRootFS RO:true Compressed:false Version: 0 Size: 4194304 (4194304 with padding) Disk Offset: 34603008 (sector 67584) Load Address: 0x02200000 Checksum: 0x14169514 Firmware 11: Audio RO:true Compressed:false Version: 0 Size: 3243056 (3243520 with padding) Disk Offset: 103809024 (sector 202752) Load Address: 0x01b00000 Checksum: 0x0dd71a22 Firmware 12: RescueAudio RO:true Compressed:false Version: 0 Size: 3243056 (3243520 with padding) Disk Offset: 176160768 (sector 344064) Load Address: 0x01b00000 Checksum: 0x0dd71a22 Firmware 13: RescueKernel RO:true Compressed:false Version: 0 Size: 8983912 (8984064 with padding) Disk Offset: 108003328 (sector 210944) Load Address: 0x03000000 Checksum: 0x37f0c764
Building the Kernel
In the same WD source package referenced above, a working 4.1.17 Kernel tree can be found at linux-kernel/linux-kernel/. To get it to compile I had to install an old gcc-4.8 from Jessie
echo "deb http://archive.debian.org/debian jessie main contrib non-free" > /etc/apt/sources.list.d/jessie.list apt-get update && apt-get install gcc-4.8
Some components of the provided Kernel are very verbose by default - namely the RTC driver and the network driver. This patch comments a bunch of verbose outputs.
I also created a .config file which includes all modules to get Docker running along with NFS+CIFS filesystem modules.
The build process is no different than any other Kernel compile:
make menuconfig make -j4 Image make -j4 modules dtbs DTC_FLAGS="-p 8192" make modules_install
Before a Kernel is made permanent in the boot FW_TABLE it is advisable to copy everything to a USB stick and see if the Kernel actually boots. (e.g. using the original install USB stick without!!! the OMV directory as we don't want to re-install)
cp arch/arm64/boot/Image /dev/sda1/sata.uImage cp arch/arm64/boot/dts/realtek/wd-monarch-1GB.SATA.dtb /dev/sda1/rescue.sata.dtb
NOTE: in some cases I had to unplug the device for the boot to succeed - a reboot didn't get the device up! I Believe having seen some similar remarks in the community forum.
Installing the Kernel
To permanently install the Kernel it has to be copied to the appropriate partition along with the device tree config. The above mentioned fwtablectl will then fix the checksums in the FW_TABLE.
dd if=arch/arm64/boot/Image of=/dev/sataa8 dd if=arch/arm64/boot/dts/realtek/wd-monarch-1GB.SATA.dtb of=/dev/sataa6 fwtablectl-arm64 firmware update /dev/sataa1 RescueKernel arch/arm64/boot/Image fwtablectl-arm64 firmware update /dev/sataa1 RescueDeviceTree arch/arm64/boot/dts/realtek/wd-monarch-1GB.SATA.dtb
Known Limitations
- As of now I didn't get the PWM device to work that controls the LED
