Nerveware

Disk/Image tricks
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Disk/Image tricks

Created by Bayou.

Clone disk and install onto another device

$ dd if=/dev/mmcblk0 of=mmcblk0-copy.img conv=fsync

Boot other device to NFS root file system and write to disk

$ dd if=mmcblk0-copy.img of=/dev/mmcblk0

Make sure no errors exist on the new partitions

$ for i in /dev/mmcblk0p*; do
fsck -f $i
done

Disk has problems

It might occur that the last partition is too large/small.

$ resize2fs /dev/mmcblk0p5

But if the system complains about a partition table that's corrupt, it must be solved otherwise.

$ e2fsck -f /dev/mmcblk0p5
e2fsck 1.42.5 (29-Jul-2012)
The filesystem size (according to the superblock) is 3061504 blocks
The physical size of the device is 3040000 blocks
Either the superblock or the partition table is likely to be corrupt!
$ mke2fs -S /dev/mmcblk0p5
$ fsck -y /dev/mmcblk0p5

Shrink root file system

This is kind of sketchy and you need to pay attention!

The disk /dev/mmcblk0 has a GUID partition table. EFI is on 0p1, the root file systen is on 0p2 and uses 12GB from its 23GB in size. I want to cut it somewhat in half (15GB).

$ df -h /
Filesystem      Size  Used Avail Use% Mounted on
/dev/mmcblk0p2  28.6G  13G 15.6G  45% /

Boot into Debian Live from USB (or whatever) and prepare the partition.

$ e2fsck -f /dev/mmcblk0p2
$ resize2fs /dev/mmcblk0p2 15G

The resize2fs command says how much blocks are in use.

The filesystem on /dev/mmcblk0p2 is now 3932160 (4k) blocks long.

Now we have to adjust the parition table to 3932160*4=15728640K. First check the start sector.

$ fdisk /dev/mmcblk0
p
q

As shown below, the start sector is 1050624.

Disk /dev/mmcblk0: 29,14 GiB, 31293702144 bytes, 61120512 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: gpt Disk identifier: CDF8E75B-369C-4C5E-90F6-019A7AEFE6EA Device Start End Sectors Size Type /dev/mmcblk0p1 2048 1050623 1048576 512M EFI System /dev/mmcblk0p2 1050624 61120478 60069855 28.6G Linux filesystem

Reopen fdisk and change the partition table. Make SURE that you DON'T overwrite the ext4 signature.

$ fdisk /dev/mmcblk0
d
2
n
2
1050624
+15728640K
N
w
q

Mount partition in an image

If an entire disk is copied and the data of a single partition must be checked, use the following commands to mount the specifi partition.

$ fdisk -l core-image-rpi-base-raspberrypi4-64.rpi-sdimg
Disk core-image-rpi-base-raspberrypi4-64.rpi-sdimg: 1008 MiB, 1056964608 bytes, 2064384 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x51c3f431

Device                                         Boot  Start     End Sectors  Size Id Type
core-image-rpi-base-raspberrypi4-64.rpi-sdimg1 *      8192  106495   98304   48M  c W95 FAT32 (LBA)
core-image-rpi-base-raspberrypi4-64.rpi-sdimg2      106496 2064383 1957888  956M 83 Linux
$ mount -o loop,offset=$(( 8192 * 512 )) core-image-rpi-base-raspberrypi4-64.rpi-sdimg /mnt/

Mount a jffs2 image

$ modprobe -r block2mtd

$ modprobe loop
$ A=$(losetup -f)
$ losetup $A /path/to/image.jffs2

$ modprobe block2mtd block2mtd=${A},128ki
$ B=$(cat /proc/mtd | grep $A | grep -Eo '^[^:]+')

$ C=/dev/${B/mtd/mtdblock}
$ mknod ${C} b 31 0
$ mount -tjffs2 ${C} /mnt

Mount a ubifs image

# 1GiB partition
$ modprobe nandsim first_id_byte=0xec second_id_byte=0xd3 third_id_byte=0x51 fourth_id_byte=0x95
$ ubiformat /dev/mtd0 -s 2048 -O 2048; flash_erase /dev/mtd0 0 0
$ modprobe ubi; ubiattach -m 0 -d 0 -O 2048

# 512MiB ubifs device
$ ubimkvol /dev/ubi0 -N volname -s 512MiB; ubiupdatevol /dev/ubi0_0 
$ ubiupdatevol /dev/ubi0_0 /path/to/image

$ mount /dev/ubi0_0 /mnt

Extract, change, and create uRamdisk

Note that the xz command uses 32bit crc. Use `file rootfs.xz` to determine crc32 or crc64.

mount nand1.img mnt/

#tail -c+65 mnt/rootfs.img > ./rootfs.xz
dd if=mnt/rootfs.img of=./rootfs.xz bs=64 skip=1

mkdir tmp
cd tmp
xzcat ../rootfs.xz | cpio -id

# do something with the rootfs.

find | cpio -ovH newc | xz -C crc32 > ../rootfs.new
cd ..

mkimage -A arm -T ramdisk -C none -d rootfs.new rootfs.img

Extract and check dts in HABv4 (i.MX8MP)

In flash.bin the U-Boot's device tree is the last one. The one located on 0x58000 is the ATF before u-boot.

$ mkdir tmp
$ cp /path/to/flash.bin tmp/
$ cd tmp
$ binwalk flash.bin

DECIMAL       HEXADECIMAL     DESCRIPTION
--------------------------------------------------------------------------------
37690         0x933A          Android bootimg, kernel size: 1229148160 bytes, kernel addr: 0x4C435F65, ramdisk size: 1363497547 bytes, ramdisk addr: 0x6D654D00, product name: "(4G)"
360448        0x58000         Flattened device tree, size: 863 bytes, version: 17
374640        0x5B770         CRC32 polynomial table, little endian
936789        0xE4B55         Android bootimg, kernel size: 1684947200 bytes, kernel addr: 0x64696F72, ramdisk size: 1763734311 bytes, ramdisk addr: 0x6567616D, product name: "oo long!"
943118        0xE640E         gzip compressed data, maximum compression, from Unix, last modified: 1970-01-01 00:00:00 (null date)
1143168       0x117180        Flattened device tree, size: 32886 bytes, version: 17

$ dd if=flash.bin of=dtb bs=1 skip=1143168
$ dtc -I dtb -o dts dtb

# do something

$ dd if=flash.bin of=dtb bs=1 skip=360448 count=$((374640-360448))
$ dtc -I dtb -o dts dtb
$ head -1 dts 
/dts-v1/;

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