Block based OTA update needs mtdblock

[Pintu Agarwal]

Hi All,

For one of our automotive products we have the following configuration:
QC chipset, arm64, Kernel-5.15, NAND Flash 1GB, A/B system, UBI
volumes (squashfs, ubifs), DM-verity for rootfs (squashfs), simple
busybox platform.

For OTA updates we have a strong dependency with MTD_BLOCK.

Till now, we were using ubiblock for mounting squashfs volumes and
completely got rid of mtd_block by configuring it as a loadable
module.
But, we also need to support OTA updates (Full, Incremental) on A/B
volumes using the same Android OTA framework.
https://source.android.com/docs/core/ota/nonab/block

OTA update will be applied to the B (inactive) partition.
OTA updates prefer block based update over file based especially for
dm-verity enabled devices.

Now, the problem is, on MTD we only have 2 options for block based
updates; ubi_block or mtd_block.
We cannot use ubiblock for OTA updates as it is read only.
For full update volume, we can use "ubiupdatevol" interface to
completely replace the volume content, but for partial or incremental
update we need to update only specific blocks and not entire
partitions.
Thus, we have to use the MTD_BLOCK (/dev/mtdblock) interface to
support block based OTA updates on UBI volumes.
Thus, during ota updates (only) we need to install the mtdblock
module, perform the update and then uninstall the module.

That means, we cannot completely get rid of MTD_BLOCK from our product
especially for OTA use cases.

Is this the only way, or do we have any other option to support OTA
updates over UBI volumes ?


Thank you,
Regards,
Pintu