linux-kernel - Re: Bug in mtd_get_device

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Date:	Mon, 11 Mar 2013 10:08:51 +0200
From:	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
To:	Richard Genoud <richard.genoud@...il.com>,
	"Velykokhatko, Sergey" <Sergey.Velykokhatko@...-med.de>
Cc:	Brian Norris <computersforpeace@...il.com>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ricard Wanderlof <ricard.wanderlof@...s.com>
Subject: Re: Bug in mtd_get_device_size()?

On Fri, 2013-03-01 at 15:29 +0100, Richard Genoud wrote:
> > Unfortunately I have no additional information why it happened, but
> anyway is it really necessary to runs ubiformat+ubimkvol for such
> cases? Or is it possible to recover data?
> I honestly don't know, but I'm sure Artem has some idea on that.

Everything should work in theory. If there are issues, they should be
looked at and investigated. I do not have any better suggestion off the
top of my head.

> >Since my solution for this case is to put the device data in separate MTD with one single UBI volume. But you know how much space I should reserve on NAND MTD for single XML-File with 200Bytes :-).
> I've got the same problem with uboot environment for example. It's
> only some hundred bytes, and still I have to reserve the maximum bad
> blocks number + 1 for the environment itself (so for your device 41).
> I know, this looks overkill...
> For 200bytes, I would try to store them elsewhere (spi dataflash,
> eeprom...) if there's such devices on your board.
> There's also the 1st block of the nand device which is guaranteed to
> be "valid" for 1000 erase cycles (valid with 1-bit ECC per 528 bytes)

The ideal solution would be to not partition the chip at all, of course.

BTW, if we ara talking about a device for medicine with tens of years of
lifetime, you need to be careful about read disturb issues. In the MTD
web site we discuss them - and there is a suggestion to read whole UBI
device from time to time to force scrubbing.

> > Alternative is to try to mount only device volume, copy data in tmpfs, run ubiformat+ubimkvol+mount and copy the data back to the device volume. Or you have other idea?

Not sure why this would be needed. We did not do any on-flash format
breakage AFAIK. But I admit I did not read this thread carefully.

Sergey, feel free to ask specific questions in separate threads, to make
it easier to answer them.

-- 
Best Regards,
Artem Bityutskiy

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