Here is simple step to create a custom partition with AVB.
Tested by i.MX8MN EVK and Android P9.0.0_2.3.1.
Create image for xyz partition in 1024MB in Android build output folder
# cd $OUT
# mkdir xyz
# echo "This is test txt file" > xyz/Readme.txt
# make_ext4fs -l 1073672192 -s -a xyz xyz.ext4.img xyz
Apply the attached patch. uboot patch corrects the reading problem on avb footer.
Flash images by uuu
# cd $OUT
# sudo ./uuu_imx_android_flash.sh -f imx8mn
Check result.
Boot up and mount xyz partition
# cd /data
# mount /dev/block/mmcblk2p14 xyz
# cat xyz/Readme.txt
This is test txt file
