Re: [PATCH 4/5] UBI: introduce attach ioctls

[Artem Bityutskiy <dedekind@infradead.org>]

On Wed, 2007-12-19 at 16:57 +0100, Arnd Bergmann wrote:
> > 
> > If the MTD device is already UBI-formatted, the numbers may be read from
> > the media. Otherwise, not.
> 
> Ok, let me suggest an idea, it probably needs more refinement, but maybe we
> can come up with something better based on this:
> 
> You can have a simple attribute named 'ubi-probe' in each MTD device in sysfs.

Err, why should MTD know something about what sits on top of it? Today
it is UBI, tommorrow it is something new and better, e.g., more
scalable.

> this is only readable, and contains either '0' or '1' in ascii, telling you
> whether a UBI device could be found for this device.

So MTD maintains ubi-probe attribute, and has some knowlege about UBI.
Well, it is technically possible, but I do not think it would be good
design. The same way we could teach MTD to probe if it has JFFS2 on it,
or something else...

> This only works for UBI formatted media, and the kernel does not format the
> media itself.
> IF you want to UBI-format a medium, use a user space tool that writes the
> appropriate blocks directly to the /dev/mtd* character device.

Yeah, user-space tools could format media. But it is so much appropriate
facility to have UBI being able to format it itself. It is really very
convenient. Flashes have special state - empty flash, and if the flash
is empty - UBI make it UBI-formatted. If the flash has some garbage -
UBI does not format it. 

-- 
Best regards,
Artem Bityutskiy (Битюцкий Артём)