Re: UBIFS: recovery of master node

[Richard Weinberger <richard@nod.at>]

Am 17.07.2015 um 08:58 schrieb Andrea Scian:
> Il 16/07/2015 17:29, Richard Weinberger ha scritto:
>> Andrea,
>>
>> On Thu, Jul 16, 2015 at 3:22 PM, Andrea Scian <rnd4@dave-tech.it> wrote:
>>>
>>> If I bypass that check too, I can mount UBIFS and everything inside the FS
>>> is there but, of course, I'm sure I'm doing something that may be wrong..
>>>
>>> WDYT?
>>
>> So, you're facing bitflips on empty space?
> 
> Another UBI/UBIFS "implementation" question: are there some other places, apart from get_master_node(), where UBIFS check empty space corruption and fails badly if something wrong?

Having non-corrupted empty space is a fundamental requirement of UBIFS.
If you patch it out you'll hurt UBIFS's ability to recover from a power cut.
Someone tried to do so already.

I know, cheap modern NAND, especially MLC seems to show bitflips also on empty pages.
Not all NAND controllers can deal with that and will just return an uncorrectable ECC error
upon reading.
IMHO the right place to deal with that is MTD core.
Please search the archives, Brian posted some patches some time ago.

Thanks,
//richard