Re: jffs2, mtd, mtd-utils and ancient kernels

[Richard Weinberger <richard.weinberger@xxxxxxxxx>]

Don,

On Tue, Oct 15, 2019 at 3:01 AM <don311@xxxxxx> wrote:
>
> Greetings,
>
> I apologize for writing my first post here on a topic you've made
> abundantly clear, for a long _long_ time now, that you have no interest
> in: support for ancient kernels.  If it helps, let me be clear that I'm
> not looking for "support" in quite the usual sense, but I have what I
> think are a couple pretty basic questions.  I've tried downloading and
> searching through the mailing list archives going back to the era that
> the device I'm working on was originally developed (2004) without much
> luck.  Google hasn't been much help with this either.  Of course it's
> possible I just wasn't searching for the right things.
>
> Basic questions:
>
> Q1/ From what I've read, before MTD, JFFS2, and mtd-utils source code
>     moved to Git in 2006, it was in CVS, and snapshots were available
>     here:
>         ftp://ftp.uk.linux.org/pub/people/dwmw2/mtd/...
>     That doesn't seem to work any more (hardly surprising, I guess,
>     after so long), but I'm wondering: Might those old snapshot archives
>     still be available somewhere else?  I don't see any mention of it on
>     the current web site.

Maybe David knows. CC'ed.

For kernel stuff, see:
https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/

> Q2/ Is there anything you can point me to that shows which versions of
>     MTD, JFFS2, and mtd-utils were delivered for use with each Linux
>     kernel release?  In my case, I have particular interest in kernel
>     2.4.26 -- so would it be possible to, say, find the mtd-utils
>     version that corresponds to the version of MTD and JFFS2 used in
>     2.4.26?

Usually Debian is a good source for such an information.
...or any other Linux distro with long term archives.

> Slightly more detailed historical questions -- if any of you are still
> reading, and happen to remember back that far:
>
> Q3/ The JFFS2 code in 2.4 is referred to in several places (web site and
>     mailing list) as stable, but does anyone here know/remember whether
>     its "on-disc" (er, "on-flash") format continued to stay stable after
>     2.4?  Put another way, how compatible (forwards and backwards) are
>     JFFS2 images between 2.4 and later?
>       - On the forward side, if one upgraded the kernel on a device that
>         had been running 2.4.x (x >= 26) to something later, could the
>         file system be used as-is?  (I mean, without risk of an ensuing
>         mess?)

We try hard to stay compatible and use versioning. So I'd assume that a
recent kernel still can mount an old filesystem.
If not, please report.

>       - On the backward side, how dangerous would it be to use a 2.4.26
>         kernel with a new (never mounted) JFFS2 image built with a later
>         version of mkfs.jffs2?  (Not that one would deliberately choose
>         such to do a thing, of course.)  I've built 2 or 3 different
>         versions and found that they generate much different images from
>         a constant "source" directory tree, but I haven't yet tried to
>         dissect the images to understand the differences.

As long you don't enable newer features in mkfs, it should work too.

> Q4/ The JFFS2 code in 2.4 is also referred to as well tested.  Is anyone
>     here aware of whether that extends to the area of random hardware
>     resets / power cuts, such as might be experienced on embedded
>     devices without reliable power sources?  I see there were many
>     performance improvements and bug fixes over the years, but are you
>     aware of any data about relative reliability -- on the same hardware
>     -- of JFFS2 in 2.4 vs much later / current, say?  (I believe "on the
>     same hardware" would imply nor flash here, since 2.4 didn't support
>     nand.)

You *really* don't want to use a 2.4 kernel.

> I'd be happy to explain what sorts of colorful pharmaceuticals I've been
> into that could cause me to ask such questions, but I suspect the above
> may be enough flame-inducing stuff for one post.

I'm all ear. :-)

-- 
Thanks,
//richard

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