linux-kernel - MTD: How to get actual image size from MTD partition

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Message-ID: <CAOuPNLjzyG_2wGDYmwgeoQuuQ7cykJ11THf8jMrOFXZ7vXheJQ@mail.gmail.com>
Date:   Fri, 16 Jul 2021 12:12:41 +0530
From:   Pintu Agarwal <pintu.ping@...il.com>
To:     open list <linux-kernel@...r.kernel.org>,
        linux-mtd <linux-mtd@...ts.infradead.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Phillip Lougher <phillip@...ashfs.org.uk>,
        Sean Nyekjaer <sean@...nix.com>,
        Kernelnewbies <kernelnewbies@...nelnewbies.org>,
        Richard Weinberger <richard@....at>
Subject: MTD: How to get actual image size from MTD partition

Hi,

Our ARM32 Linux embedded system consists of these:
* Linux Kernel: 4.14
* Processor: Qualcomm Arm32 Cortex-A7
* Storage: NAND 512MB
* Platform: Simple busybox
* Filesystem: UBIFS, Squashfs
* Consists of nand raw partitions, squashfs ubi volumes.

My requirement:
To find the checksum of a real image in runtime which is flashed in an
MTD partition.

Problem:
Currently, to find the checksum, we are using:
$ md5sum /dev/mtd14
This returns the proper checksum of the entire partition.
But we wanted to find the checksum only for the actual image data
which will be used by our C utility to validate the image.
Here, we don't know the actual image size.
We only know the "partition-size" and "erasesize".

So, is there a mechanism to somehow find the image size at runtime?

Regards,
Pintu