On Thu, Jul 22, 2021 at 1:11 PM Pintu Agarwal [off-list ref] wrote:

On Thu, 22 Jul 2021 at 02:24, Richard Weinberger [off-list ref] wrote:

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But let me advertise ubiblock a second time.

Sorry, I could not understand about the ubiblock request. Is it
possible to elaborate little more ?
We are already using squashfs on top of our UBI volumes (including
rootfs mounting).
This is the kernel command line we pass:
rootfstype=squashfs root=/dev/mtdblock44 ubi.mtd=40,0,30
And CONFIG_MTD_UBI_BLOCK=y is already enabled in our kernel.
Do we need to do something different for ubiblock ?

From that command line I understand that you are *not* using squashfs on top of UBI.
You use mtdblock. ubiblock is a mechanism to turn an UBI volume into a read-only
block device.
See: http://www.linux-mtd.infradead.org/doc/ubi.html#L_ubiblock

Okay, you mean to say, we should use this ?
ubi.mtd=5 ubi.block=0,0 root=/dev/ubiblock0_0
Instead of this:
root=/dev/mtdblock44 ubi.mtd=40,0,30

Yes. But it is not only about a different command line. It is a
different concept.
You use a emulated block device on top of UBI, and not directly on top
of an MTD part.

Sorry, I could not get this part. How static volume can give image len ?
You mean there is some interface available in kernel to get actual image len ?

use the ubinfo tool. Static volumes know exactly how much they are filled.

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Also, how can we get the checksum of the entire UBI volume content
(ignoring the erased/empty/bad block content) ?

Just read from the volume. /dev/ubiX_Y.

I think this also will give the entire volume size, but we still don't know how
many pages have real data ?

"ubiinfo /dev/ubiX_Y" will tell you if the volume is of type static.

For example:
Suppose, my raw partition/volume is of size 10MB
But my actual data inside it is of size ~3MB (may be split across?)
Then, how can we get the actual size of the data content ?

See above.

You mean to say: /dev/ubiX_Y should contain only data blocks ?

Yes. An UBI volume contains only "user data".

-- 
Thanks,
//richard

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