JFFS2: file contents in case of data CRC error

Korolev, Alexey alexey.korolev at intel.com
Fri Feb 1 10:53:42 EST 2008


>> Could you please give information about how you can get this error? I
>> need to know use case. 
> The issue has been reported by a customer working on PPC405EP-based 
> system running linux 2.4.20.
> The device under test has run a temperature cycle test. The
> has been varied in the whole industrial range (-40/+85 deg C). After 
> completing the test, the files stored on NAND have been read back and 
> compared to the original ones - written on NAND before starting the 
> temperature test - and the difference in the file f.img previously 
> described arose.

Ahh. The temperature tests. That explains a lot. 
Probably device worked improperly in the test but test did not turn off
device when NAND become unworkable. As result JFFS2 did not detect the
problem of broken CRC on mount but did it on attempt to read the broken
data and printed error message. 

So JFFS2 performed scan on read - found CRC error in node 
-> JFFS2 marked node to be obsolete
-> As result hole in the file has been formed. 
-> You read 0x0 in the middle of the file. 

I think nobody considered such tests before. I am not sure if any file
system may be reliable in such a case with temperature tests.

Unfortunately I have no idea how this issue could be solved :).

>>> to NAND. In fact, in the middle of the file, I see a 4-kByte "hole" 
>>> where all bytes are 0.
>> It is Ok. NAND error correction could return that data is correct
>> if it is not correct. It finds the issues with guarantee only in case
>> 1 or 2 bits errors.  
> About this point I agree with catboat 
> (http://article.gmane.org/gmane.linux.drivers.mtd/19463). In my
> in this case JFFS2 should report an error code != 0 in order to warn
> userland that something did not work perfectly.
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