mount time (was Re: Fwd: Hello -- NAND/NOR Flash design for GTA02)

[Werner Almesberger]

Andy Green wrote:
> You're right... I don't know if we already run sumtool as part of
> generating the FS image.  It's possible since we have the config option
> enabled.

Seems that we don't use it. One more thing to try.

> It seems from Googling around that it is a one-off advantage that will
> degrade as files get updated, but that doesn't mean it isn't worth having.

As far as I understand the mechanism, performance should be good
if we have only few changes. Eventually, one would have to run
"sumtool" again. A bit like defragmentation under Windows :-)

I'm not sure yet if it is compatible with writing the rootfs as an
image, though. The issue is as follows:

We generate the rootfs as an image on "perfect" storage. We then copy
it to NAND skipping bad blocks. Thus, blocks at positions X and Y in
the original image will end up at positions X' and Y', with |X-Y| =
|X'-Y'|+N where N is the number of bad blocks between X' and Y'.

Thus any use of some sort of "pointer" isn't trivially compatible
with this.

In HXD8, which uses YAFFS2 for the large data partitions, we avoid
this problem by bringing up Linux and writing the files through the
filesystem, on the actual device.

This may also be an option for GTA02, but it would change a few
rather well-established processes.

- Werner