JFFS2: checking CRCs twice!?

[Steven Scholz]

Hi Ferenc,

Ferenc Havasi wrote:

> If I am right there are two kind of CRC: hdr_crc and node_crc. At 
> mounting time only the hdr_crc is checked which depends on only the 
> header. (using summary there is only one summary CRC check)
> 
> Later (when the data is readed or in the background by GC) the node_crc 
> will also be checked. GC is running on a "niced" (10) priority, so it 
> should not disturb any other process.
Well, it does. On small, slow systems.

> If I am right the CRC protects against unclean reboots and hardware 
> corruptions. If you need we can modify the summary patch not to check 
> node_crc for summarized nodes (where the unclean reboots is no problem), 
That would be nice.

> but if we do it you lose the ability to detect the hardware corruption 
> (flash errors). Unfortunatelly NOR flash doesn't have any error detection.
Well. I think when a sectors gots written correctly (and summary is correct), I 
have to assume that the sector stay intact. So no need for checks.

If a sector got broken just by reading it then the whole embedded system is 
broken and has to be replaced ...

-- 
Steven Scholz