For UBIFS users: be aware of write-back!

[David Woodhouse]

On Fri, 2008-10-03 at 10:45 +0300, Artem Bityutskiy wrote:
> "In contrast, JFFS2 does not have write-back support and all the JFFS2
> file system changes go the flash synchronously. Well, this is not
> completely true and JFFS2 does have a small buffer of a NAND page
> size, but it is small and we may treat JFFS2 as completely
> synchronous."

That's quite poorly phrased. You may _not_ treat JFFS2 as completely
synchronous. You treat it like a normal file system, or it's going to
eat your babies.

There was a reason I was perfectly happy to make the change which made
JFFS2 start requiring fsync() like normal file systems -- it was because
people should have been doing it _anyway_.

Anyone who was skipping the required sync handling because they 'knew'
that it didn't matter on JFFS2, even though it didn't cost them anything
anyway -- and who didn't wake up at 3am every morning in a cold sweat,
worrying that it might have broken today -- deserves to be taken out
back and shot.

When it comes to correctness, people shouldn't have to do anything
special for different file systems. If there is _anything_ fs-specific
about the correctness issues, you are doing something WRONG (cf. NFS).

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse at intel.com                              Intel Corporation