Get rid of crazy empty tag_list element at the start

[Linus Torvalds]

On Mon, Mar 10, 2014 at 11:28 AM, Dirk Hohndel <dirk at hohndel.org> wrote:
>
> Would you mind adding a commit message and SOB?

The first patch had it already, the second patch is identical except
for just the trivial fixes. But here does.

          Linus

---
Subject: Get rid of crazy empty tag_list element at the start

So this is totally unrelated to the git repository format, except for
the fact that I noticed it while writing the git saving code.

The subsurface divetag list handling is being stupid, and has a
initial dummy entry at the head of the list for no good reason.

I say "no good reason", because there *is* a reason for it: it allows
code to avoid the special case of empty list and adding entries to
before the first entry etc etc.  But that reason is a really *bad*
reason, because it's valid only because people don't understand basic
list manipulation and pointers to pointers.

So get rid of the dummy element, and do things right instead - by
passing a *pointer* to the list, instead of the list. And then when
traversing the list and looking for a place to insert things, don't go
to the next entry - just update the "pointer to pointer" to point to
the address of the next entry. Each entry in a C linked list is no
different than the list itself, so you can use the pointer to the
pointer to the next entry as a pointer to the list.

This is a pet peeve of mine. The real beauty of pointers can never be
understood unless you understand the indirection they allow. People
who grew up with Pascal and were corrupted by that mindset are
mentally stunted. Niklaus Wirth has a lot to answer for!

But never fear. You too can overcome that mental limitation, it just
needs some brain exercise. Reading this patch may help. In particular,
contemplate the new "taglist_add_divetag()".

Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>