JFFS2: checking CRCs twice!?

[Artem B. Bityuckiy]

On Wed, 12 Jan 2005, Steven Scholz wrote:

> 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 ...
This seems to be true for NOR. But  chrcking CRC helps at least *detect* 
and *report* media problems.

> 
> -- 
> Steven Scholz
> 
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> 

--
Best Regards,
Artem B. Bityuckiy,
St.-Petersburg, Russia.