JFFS3 & performance

[Artem B. Bityuckiy]

On Thu, 13 Jan 2005, [iso-8859-1] Jörn Engel wrote:

> On Thu, 13 January 2005 15:05:16 +0000, Artem B. Bityuckiy wrote:
> > On Thu, 13 Jan 2005, Artem B. Bityuckiy wrote:
> > 
> > > See the benefits:
> > > 1. We are able to use weaker then CRC32 checksums and still be good in 
> > > detecting wrong due to unclean reboot nodes.
> > > 2. We have principal ability to distingush between nodes corrupted due to 
> > > flash problems and due to unclean reboots.
> > > This is extreemly good do be able to distinguish. (JFFS2 has no such 
> > > ability). 
> 
> Right, very nice attributes.
> 
> > > Thoughts?
> > Hmm, only one small note, putting CRC to the end does not allow us to 
> > recognize unclean reboots and flash media corruptions :-) But we still may 
> > do this putting some majic bitmask to the end of nodes.
> 
> static uint32_t jffs3_checksum(...)
> {
> 	static uint32_t ret = do_jffs3_checksum(...);
> 	if (ret == 0xffffffff)
> 		return 0;
> 	return ret;
> }
> 
> When reading the node, simply compare the checksum to 0xffffffff.  If
> it matches, we know that
> a) the checksum is wrong and 
> b) it was due to incomplete write, not flash corruption.
> 
> Adler32 has the nice property that 0xffffffff is an impossible
> checksum by design already, so the above code wouldn't be necessary.
Yes, I thought so either. But imagine due to unclean reboot the last CRC 
was not written completely. this is the problem.
> 
> Jörn
> 
> -- 
> ...one more straw can't possibly matter...
> -- Kirby Bakken
> 

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