Query: UBIFS: How to detect empty volumes

[Pintu Agarwal]

Hi,

I have one basic query related to UBIFS volumes on a system with NAND
partition.
In short, how to detect a particular empty volume inside a system partition
while flashing the partition image?

Suppose I have one big system partition that consists of 4-5 ubi volumes
inside it with varying sizes.
Lets say:
-- System Partition (ubi image)
    - rootfs volume (ro, squashfs)
    - data volume (rw, ubifs)
    - firmware volume (ro, ubifs)
    - some-other volume (ro, squashfs)

Consider that all these could be flashed together as part of system.ubi
image in a single shot from the bootloader.
Now, suppose, one of the volume image (say firmware) is missing or remains
empty (as you know we can have empty volumes).

So, during system image flashing, we wanted to detect if one of the volume
(firmware) is empty.
Since this is an important volume, so we wanted to detect if this volume is
empty/missing we will abort flashing the system partition.
As there is no point in booting the system without this partition.

So, I am exploring options, how can this be detected ?
I mean is there any kind of magic number or header information which we can
read to detect a particular empty volume ?
Can we get any information from just "system.ubi" image to indicate about
the volume information ?
Also it could be possible that 2 or more volumes are empty, but we are only
concerned about one particular volume (firmware), so how to detect
particular volume ?

If anyone has any thoughts about this requirement, please share your
opinion.


Thanks,
Pintu
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