[Yaffs] Make YAFFS2 work as a root FS, patch

[Sergey Kubushyn]

On Thu, 27 Oct 2005, Martin Fouts wrote:

First of all, please don't take it as an abuse.

> > > You were, by the way, mistaken.  Linux kernel will mount YAFFS2
> > > filesystem without it.  However, when the read of the mtd
> > super struct
> > > fails, the error returned (EPERM) will be confusing to the end
> user.
> >
> > No, it will not.
> >
> > All the filesystems known to the kernel at bootup are tried
> > in turn. YAFFS comes before YAFFS2 so before YAFFS2 is tried
> > kernel gets an error from YAFFS that is -1 i.e. -EPERM now.
> > That breaks the loop and make the kernel panic.
>
> Hi Sergey,
>
> Guess we got caught in the terminology thing.  To *me* YAFFS2 is
> version
> 2 of the YAFFS source code base, which works for both 512 byte and 2k
> byte page size file systems.  In that sense, YAFFS2 *will* work.

Yes, this is an acceptable excuse. Barely but acceptable.

> Also, it is possible to build for 2k devices without building for 512
> bytes pages.  In that sense, YAFFS2 *will* work.

Not with the current source. It does NOT build without YAFFS1 support (at
least it didn't a couple of weeks ago.) And no matter what they both are
registered with the kernel because of commented out conditionals in CVS
code.

Again, nice try but failed.

> But, you mention reading source code.  Perhaps you should read man
> pages.  If you specify the -t option to mount, it does not try all file
> system types, but tries the one you specify, so even if you've built a
> YAFFS2 file system that handles both 512 byte and 2k devices, you could
> still mount a 2k device, even with the bug in place.

OK, please explain how can one mount _ROOT_ filesystem with "mount -t". Try
to explain where that "mount" comes from if the root FS is not mounted.
Just to counter a possible excuse and to avoid emailing twice - you do NOT
mount a _ROOT_ YAFFS (or ext2 or whatever it is) filesystem when booting
with initrd. That's initrd that contains a root filesystem. You mount the
other filesystem elsewhere and only then you pivot_root() to it.

There is only one way to mount the root filesystem. And there is no way to
tell "-t yaffs2" to the kernel. At least without some unconventional
trickery.

> In fact, of the many ways to build and install YAFFS2, there is only
> one
> in which it won't mount a file system.  Had you put more information
> and
> less vitriol into your email, I would have realized that you were in
> that one circumstance.  It's hard to read your mind, and your attitude
> makes it undesirable to try.
>
> I mention this, Sergey, because it seems to be the root of your
> misunderstanding about how fragile YAFFS is.  You seem to think that
> there is only one way to use a file system -- yours -- and if it breaks
> when being used that way, it can't work any other way.

No, I don't. There is only one way to mount a _ROOT_ FS, yes. I simply don't
understand how else could've I made it more clear.

> So yes, Sergey, as things stood until your patch, if you tried to use
> YAFFS2 as the root file system on a 2k NAND device, your kernel
> wouldn't
> boot.  Too bad you hadn't thought to tell us that was the set of
> circumstances you were running under.  Among other things, it would
> have
> given me the basis for a test case to add to a regression suite for
> yaffs.

Eh... Prove me wrong, but the word "ROOT" is all over my email. And subject
says _root_ .

> The patch is in my tree.  As soon as I test it, it'll get pushed.  Now
> that you've taken the time to identify exactly what you were doing,
> I'll
> see about making it a test case.  (We don't have 2k parts here at
> PalmSource, so it will be difficult for me to test.)

This one is trivial. It DOES work. It doesn't even deserve any special
mentioning. There are much more serious bugs in YAFFS. Some of them are
probably fixable although requiring a rework, not just fix (those infamous
_padded_ structures casted to (char *), (__u8 *) etc. left and right), some
are probably not (logical errors, design flaws.)

It is downright stupid to get abused by someone's pushing. If I were so
easily abused by any rant I would've quit any programming long-long ago and
shot myself to death with a cucumber. You guys should've watched real rants
and holy wars in lkml, those are for real... VFS remodelling, DevFS, lot of
other stuff...

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