JFFS2 Format Documentation?

JFFS2 Format Documentation?

[Phil Thompson]

Is there a document anywhere describing the format of a JFFS2 filesystem? 
Google didn't come up with anything.

I'm happy to write one if it doesn't already exist.

Thanks,
Phil

Re: JFFS2 Format Documentation?

[Henrik Nordstrom]

Maybe this is what you are looking for?

   http://sources.redhat.com/jffs2/

Regards
Henrik Nordström


tis 2003-01-28 klockan 10.56 skrev Phil Thompson:
> Is there a document anywhere describing the format of a JFFS2 filesystem? 
> Google didn't come up with anything.
> 
> I'm happy to write one if it doesn't already exist.
> 
> Thanks,
> Phil
> 
> ______________________________________________________
> Linux MTD discussion mailing list
> http://lists.infradead.org/mailman/listinfo/linux-mtd/
-- 
Henrik Nordstrom <hno@marasystems.com>
MARA Systems AB

Re: JFFS2 Format Documentation?

[Phil Thompson]

David's paper is a good start but I was after a lower level of detail. I need 
something from which I can implement a JFFS2 reader from scratch (ie. without 
any GPL code).

Phil

On Tuesday 28 January 2003 11:10 am, Henrik Nordstrom wrote:
> Maybe this is what you are looking for?
>
>    http://sources.redhat.com/jffs2/
>
> Regards
> Henrik Nordström
>
> tis 2003-01-28 klockan 10.56 skrev Phil Thompson:
> > Is there a document anywhere describing the format of a JFFS2 filesystem?
> > Google didn't come up with anything.
> >
> > I'm happy to write one if it doesn't already exist.
> >
> > Thanks,
> > Phil
> >
> > ______________________________________________________
> > Linux MTD discussion mailing list
> > http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: JFFS2 Format Documentation?

[Jörn Engel]

On Tue, 28 January 2003 12:35:27 +0000, Phil Thompson wrote:
> 
> David's paper is a good start but I was after a lower level of detail. I need 
> something from which I can implement a JFFS2 reader from scratch (ie. without 
> any GPL code).

Good luck! ;-)

Honestly, if that document does not exist (I bet you, it doesn't) you
will have to create it yourself, pay someone to do it or go through
some other pain. Plus you will end up with a possibly incompatible
version.

Do this only after you checked the possibilities of going GPL and
licensing the code for money, as a last resort. And even then, don't
feel happy about your choice.

Jörn

-- 
Don't worry about people stealing your ideas. If your ideas are any good,
you'll have to ram them down people's throats.
-- Howard Aiken quoted by Ken Iverson quoted by Jim Horning quoted by
   Raph Levien, 1979

Re: JFFS2 Format Documentation?

[David Woodhouse]

phil@river-bank.demon.co.uk said:
> David's paper is a good start but I was after a lower level of detail.
> I need  something from which I can implement a JFFS2 reader from
> scratch (ie. without  any GPL code). 

The on-medium format is very simple. The actual layout of the existing node 
types is detailed in full in include/linux/jffs2.h. In conjunction with the 
theory of operation described in the paper, these should be perfectly 
sufficient.

What exactly are you trying to achieve? Simple read-only operation or a 
fully-functional compatible file system?

--
dwmw2

Re: JFFS2 Format Documentation?

[Brian J. Fox]

   From: David Woodhouse <dwmw2@infradead.org>
   Date: Tue, 28 Jan 2003 13:44:46 +0000

   phil@river-bank.demon.co.uk said:
   > David's paper is a good start but I was after a lower level of detail.
   > I need  something from which I can implement a JFFS2 reader from
   > scratch (ie. without  any GPL code). 

   The on-medium format is very simple. The actual layout of the
   existing node types is detailed in full in include/linux/jffs2.h.
   In conjunction with the theory of operation described in the paper,
   these should be perfectly sufficient.

Perhaps he can't read that header file without "contaminating" his
clean-room implementation?

Phil?

Brian
--
More people use Apache than Word, and it does them more good.
  Kragen Sitaker, Mon, 04 Nov 2002 21:32:18 -0800

Re: JFFS2 Format Documentation?

[Phil Thompson]

On Tuesday 28 January 2003 1:44 pm, David Woodhouse wrote:
> phil@river-bank.demon.co.uk said:
> > David's paper is a good start but I was after a lower level of detail.
> > I need  something from which I can implement a JFFS2 reader from
> > scratch (ie. without  any GPL code).
>
> The on-medium format is very simple. The actual layout of the existing node
> types is detailed in full in include/linux/jffs2.h. In conjunction with the
> theory of operation described in the paper, these should be perfectly
> sufficient.
>
> What exactly are you trying to achieve? Simple read-only operation or a
> fully-functional compatible file system?

I need to modify a bootloader to load the kernel from a JFFS2 filesystem - so 
a simple read is all that is needed. Unfortunately the bootloader doesn't 
have a license that is compatible with the GPL.

Phil

Re: JFFS2 Format Documentation?

[David Woodhouse]

bfox@ua.com said:
>  Perhaps he can't read that header file without "contaminating" his
> clean-room implementation?

I don't think we can argue that the node layout on the medium, as described
in that file, could possibly be considered sufficient to 'contaminate' an
alternative implementation.

--
dwmw2

Re: JFFS2 Format Documentation?

[David Woodhouse]

phil@river-bank.demon.co.uk said:
>  I need to modify a bootloader to load the kernel from a JFFS2
> filesystem - so  a simple read is all that is needed. Unfortunately
> the bootloader doesn't  have a license that is compatible with the
> GPL.

Which bootloader, which licence?

Note http://sources.redhat.com/jffs2/jffs2-licence.html makes it more like 
the LGPL than GPL.

--
dwmw2

Re: JFFS2 Format Documentation?

[Henrik Nordstrom]

tis 2003-01-28 klockan 15.11 skrev Phil Thompson:

> I need to modify a bootloader to load the kernel from a JFFS2 filesystem - so 
> a simple read is all that is needed. Unfortunately the bootloader doesn't 
> have a license that is compatible with the GPL.

Another idea: You could do a two stage boot loader process.. the
(non-GPL) bootloader just loads another bootloader which knows how to
read JFFS2, or replace the bootloader entirely..

-- 
Henrik Nordstrom <hno@marasystems.com>
MARA Systems AB

Re: JFFS2 Format Documentation?

[David Woodhouse]

hno@marasystems.com said:
>  Another idea: You could do a two stage boot loader process.. the
> (non-GPL) bootloader just loads another bootloader which knows how to
> read JFFS2, or replace the bootloader entirely.. 

FWIW the eCos (and hence RedBoot) JFFS2 code was updated very recently, all 
that's preventing RedBoot from reading and writing JFFS2 file systems is 
the lack of a small wrapper to actually _ask_ it to mount/read/write from 
the RedBoot prompt. 

--
dwmw2