The conditions got reserved. Also make rb_next() and rb_prev() check
for the empty condition.
Signed-off-by: NJens Axboe <axboe@suse.de>

Since rb_insert_color() is part of the _public_ API, while the others are
purely internal, switch to be consistent with that.
Signed-off-by: NDavid Woodhouse <dwmw2@infradead.org>

We only used a single bit for colour information, so having a whole
machine word of space allocated for it was a bit wasteful. Instead,
store it in the lowest bit of the 'parent' pointer, since that was
always going to be aligned anyway.
Signed-off-by: NDavid Woodhouse <dwmw2@infradead.org>

Observe rb_erase(), when the victim node 'old' has two children so
neither of the simple cases at the beginning are taken.

Observe that it effectively does an 'rb_next()' operation to find the
next (by value) node in the tree. That is; we go to the victim's
right-hand child and then follow left-hand pointers all the way
down the tree as far as we can until we find the next node 'node'. We
end up with 'node' being either the same immediate right-hand child of
'old', or one of its descendants on the far left-hand side.

For a start, we _know_ that 'node' has a parent. We can drop that check.

We also know that if 'node's parent is 'old', then 'node' is the
right-hand child of its parent. And that if 'node's parent is _not_
'old', then 'node' is the left-hand child of its parent.

So instead of checking for 'node->rb_parent == old' in one place and
also checking 'node's heritage separately when we're trying to change
its link from its parent, we can shuffle things around a bit and do
it like this...
Signed-off-by: NDavid Woodhouse <dwmw2@infradead.org>

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!