[TUHS] Re: SCO's "evidence" (was: RIP Darl McBride former CEO of SCO)

[Warner Losh <imp@bsdimp.com>]

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On Tue, Nov 5, 2024 at 10:55 AM Noel Chiappa <jnc@mercury.lcs.mit.edu>
wrote:

>     > From: Warner Losh
>
>     >> On Mon, Nov 4, 2024 at 8:14PM Larry McVoy wrote:
>
>     >> The bmap implementations I saw were bit for bit identical, same
> code,
>     >> same variables, same style, same indentation. I'm 100% sure they
> were
>     >> not independent.
>
>     > They are different in 4.3BSD. They are different in 4.2BSD (but less
>     > different). The underlying filesystems are different on disk, so they
>     > routines have to be different.
>
> That last sentence points out something important that people need to
> remember
> in this discussion: in between 4.1 and 4.2 (technically, in 4.1B), BSD
> switched to the BSD Fast File System, so I very much doubt that the
> low-level
> (i.e. logical file block to disk block) file system code in anything after
> 4.1A looks much like the AT+T low-level file system code. (I have no idea
> how
> the BSD code compares to the Linux file system code, but that's between the
> Linux people, and Berkeley.)
>

Yes. The original unix code was copied and redone somewhat. It was still
likely
a derivative work (which is why AT&T forced Berkeley to redo it for
4.4-lite), but
it was like 25% the same, 25% similar but functionally identical and 50%
new for
UFS, but filesystem layout is file system layout and some similarities
persisted.
3bsd added dtofsb() calls. 4bsd added code to make accessing the indirect
blocks
more reliable and made writing directories more reliable.  4.1 was
identical to 4bsd.
4.2 changed a lot. the 32V bmap was 112 lines long, while 4.2 was 196 lines
with
the following diffstat:
 1 file changed, 141 insertions(+), 57 deletions(-)
So by this measure, over half of the new function was new (though most of
the
comments were still the same). It did have the same structure, but
structure isn't
necessarily copyrightable since filesystem layout code will be similar
between
filesystems that are write-in-place. Looking at the diff, there's one
stretch of 15
lines that are identical, but otherwise there's changes (mostly additions)
every
few lines. A substantial re-write. These days, most open source authors
would
replace the copyright statement with their own for such an extensive rewrite
since the diff was over 2x the size of the original file (another very
imperfect
measure). Though the comments remaining identical is troublesome because
they are the parts of the code that are the most creative and subject to the
most freedom while the for loops and such are largely dictated by the
problem
or C language and customary style.

Between 4.2 and 4.3, the changes were around the edges of this function
though not in this function (I was remiss in not chasing down the bare diff
I did last night). By net.2 it was re-written again, moving most of the
function
of bmap elsewhere, so that almost nothing remained from the original 32V
in the original bmap function (though a quick grep shows that parts did move
elsewhere). In net.2 it's back down to 75 lines. shorter even than in 32V
(but
it's a bit deceptive since the code was elsewhere, though also largely
reworked).
diff reports only lines '{', '}', '/*', '*/' and a few simple assignments
(bap = bp->b_un.b_daddr;) and function calls (brelse(bp)) being the same and
all the comments different / gone from this function. Though a fair number
of
the diffs were due to changes in the "buffer cache" interface, some
formatting
changes and some substitution of #defines (like NIADDR) for bare constants
(3
in this case). These changes were also due to the role of bmap being reduced
and things like balloc being used to handle the details a fair bit
differently. And
bits of balloc do resemble bits of the original bmap, but again the
structure
had changed somewhat.

The numbers for my diffs and such are based on Krik's disks, but can also
be tested by looking at the links I posted earlier or downloading and
extracting
the sources from the TUHS archive.

The bmap() function I've extracted from different versions:

https://people.freebsd.org/~imp/pmap/pmap.32v
https://people.freebsd.org/~imp/pmap/pmap.4.2
https://people.freebsd.org/~imp/pmap/pmap.4.3
https://people.freebsd.org/~imp/pmap/pmap.net.2

Warner

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