What is the format of Android M1 Initial Preview system.img?

Question

I download Android Emulator M1 Initial Preview from https://github.com/google/android-emulator-m1-preview/releases

Inside the .app file I found api30-gphone-arm64-v8a/system.img which isn't a yaffs2 nor sparse file:

./unyaffs2 /tmp/android-wip/system.img /tmp/android-wip/system-img/

unyaffs2-0.2.8: image extracting tool for YAFFS2

image size (3232759808) is NOT a mutiple of 2048 + 64



operation incomplete

files contents may be broken

simg2img system.img.ext4 system.img

Invalid sparse file format at header magic

Failed to read sparse file

So what is the format of such file?

Updates:
Based on the direction from @Robert, I can see that the file is an fdisk image:

$ fdisk -lu system.img

Disk system.img: 3,1 GiB, 3232759808 bytes, 6313984 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: 41F73643-DBCB-41A1-A27E-9FDB53578618



Device

Start
  End Sectors Size Type

system.img1  2048
 4095
 2048
1M Linux filesystem

system.img2  4096 6311935 6307840
3G Linux filesystem

Now, it's unclear what format of the partition inside, because mount it as a regular linux partition fails:

$ sudo mount -o loop,offset=1048576 system.img /mnt/android-1

mount: /mnt/android-1: wrong fs type, bad option, bad superblock on /dev/loop17, missing codepage or helper program, or other error.

gparted also doesn't understand the partition:

— PhÆ°Æ¡ng Nguyá»…n | Sources

Answer

wrong offset, partition start at sector 4096. you can use kpartx instead

newer android running dynamic partitions. the super partition can be unpacked with Dynamic Partition Tools

furthermore partitions are flagged as read-only, therefore mount -r flag is required

sudo -i



git clone https://github.com/AndroidDumps/Firmware_extractor.git

PATH=$PATH:$(realpath Firmware_extractor/tools/Linux/bin)



mkdir -p /mnt/android-1/system_root ../extracted

kpartx -av system.img

lpunpack -p system /dev/mapper/loop2p2 ../extracted



mount -t ext4 -o loop,ro,noexec,noload,noatime ../extracted/system.img /mnt/android-1/system_root

thunar /mnt/android-1/system_root

(or whatever kpartx tell you 2nd partition is mapped)

in case you need to make ext4-dedup/logical partition writeable, increase partition first, then duplicate shared blocks

cd ../extracted

dd if=/dev/zero bs=1G seek=1 count=0 of=system.img

resize2fs system.img 1G

e2fsck -E unshare_blocks system.img

you should be able to mount -w afterwards

re-packing requires new vbmeta signature with avbtool.py stored in first partition system.img1 start at sector 2048 (which goes too far here)

superrepack third-party cross-platform tool for easy unpack/repack system.img2 is recommended to automatize the whole re-packing process

you can however do it manually with lpmake (requires all partitions to be unpacked into ../extracted see above step lpunpack)

source

resize2fs -M system.img

e2fsck -yf system.img

lpmake --metadata-size 65536 --super-name super --metadata-slots 1 --device super:3229614080 --group main:2369171456 --partition system:readonly:787050496:main --image system=system.img --partition vendor:readonly:83619840:main --image vendor=vendor.img --partition product:readonly:1366814720:main --image product=product.img --partition system_ext:readonly:131686400:main --image system=system_ext.img --sparse --output super.img

— alecxs | Sources

What is the format of Android M1 Initial Preview system.img?

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