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From: Richard Weinberger <richard@nod.at>
To: Pintu Agarwal <pintu.ping@gmail.com>
Cc: Greg KH <greg@kroah.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-mtd <linux-mtd@lists.infradead.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Phillip Lougher <phillip@squashfs.org.uk>,
	Sean Nyekjaer <sean@geanix.com>,
	Kernelnewbies <kernelnewbies@kernelnewbies.org>
Subject: Re: MTD: How to get actual image size from MTD partition
Date: Wed, 21 Jul 2021 22:54:28 +0200 (CEST)	[thread overview]
Message-ID: <2132615832.4458.1626900868118.JavaMail.zimbra@nod.at> (raw)
In-Reply-To: <CAOuPNLhti3tocN-_D7Q0QaAx5acHpb3AQyWaUKgQPNW3XWu58g@mail.gmail.com>

----- Ursprüngliche Mail -----
>> 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

>> If you place your squashfs on a UBI static volume, UBI knows the exact length
>> and you can checksum it
>> more easily.
> Yes, we use squashfs on UBI volumes, but our volume type is still dynamic.
> Also, you said, UBI knows the exact length, you mean the whole image length ?
> How can we get this length at runtime ?

You need a static volume for that. If you update a static volume the length is
known by UBI.

> 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.

> Or, you mean to say, the whole checksum logic is in-built inside the
> UBI layer and users don't need to worry about the integrity at all ?

Static volumes have a crc32 checksum over the whole content.
Of course this offers no cryptographic integrity.
See: http://www.linux-mtd.infradead.org/doc/ubi.html#L_overview

Thanks,
//richard

  reply	other threads:[~2021-07-21 20:54 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-16  6:42 Pintu Agarwal
2021-07-16  7:16 ` Richard Weinberger
2021-07-16 15:41 ` Greg KH
2021-07-16 16:26   ` Richard Weinberger
2021-07-19  9:09     ` Pintu Agarwal
2021-07-19  9:28       ` Richard Weinberger
2021-07-20  6:17         ` Pintu Agarwal
2021-07-20  6:40           ` Richard Weinberger
2021-07-20  8:01             ` Pintu Agarwal
2021-07-21 20:54               ` Richard Weinberger [this message]
2021-07-22 11:10                 ` Pintu Agarwal
2021-07-27 21:16                   ` Richard Weinberger
2021-07-29 11:17                     ` Ezequiel Garcia
2021-07-29 11:45                       ` Richard Weinberger
2021-07-29 12:03                         ` Ezequiel Garcia
2021-07-29 17:11                           ` Pintu Agarwal
2021-08-20 18:24                             ` Pintu Agarwal
2021-08-22 14:21                               ` Ezequiel Garcia
2021-08-30 15:58                                 ` Pintu Agarwal
2021-10-29 16:12                                   ` Pintu Agarwal
2021-10-29 16:48                                     ` Ezequiel Garcia
2021-11-08 13:51                                       ` Pintu Agarwal
2021-11-12 13:58                                         ` Ezequiel Garcia

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