[RFC] read-only filesystem support for NAND flash devices

[Josh Boyer]

On 5/10/06, Atsushi Nemoto <anemo at mba.ocn.ne.jp> wrote:
> On Wed, 10 May 2006 06:00:57 -0500, "Josh Boyer" <jwboyer at gmail.com> wrote:
> > Not quite the case.  You need bad block skipping, yes.  But NAND can
> > get bit flips in good blocks still.  How do you deal with that?  You
> > can't leave the block in that state forever because it will continue
> > to get bit flips and then your data will be unusable.
>
> If I mounted a JFFS2 filesystem on NAND and _never_ write anything (or
> mounted read-only), does current MTD/NAND/JFFS2 layer handle those bit
> flips?  I've thought JFFS2 only reassign blocks on writing, so JFFS2
> also suffer those "bit flips on read" problem, is it right?

If you truly never write anything, then yes it probably suffers from
the same problem.  In a typical JFFS2 setup where writes do occur, the
theory is that garbage collection will eventually reclaim that block. 
Whether that actually happens or not is largely determined on a per
use case basis.

josh