From: Linus Torvalds <torvalds@linux-foundation.org>
Newsgroups: fa.linux.kernel
Subject: Re: [PATCH RFC] struct list_node
Date: Sun, 10 Jun 2007 17:20:52 UTC
Message-ID: <fa.a/11Kt9Yh0aIA5HSukjqnJvfpsQ@ifi.uio.no>

On Sun, 10 Jun 2007, Rusty Russell wrote:
>
> The current list.h has the same type for list elements and list heads
> even though most code and coders treat them as distinct.

I think the old list.h is technically superior to yours.

Exactly *because* nodes and heads are interchangeable.

In fact, you are incorrect that "most code" treat them as distinct. Most
code that uses list.h in fact uses it as a list of entries, often without
any head at all (and each *entry* is a point of removal), because the way
to actually *find* the structure that contains the lists is separate from
the lists themselves.

In other words, I think your patch is HORRIBLY BAD, because it totally
obscures the beauty of the current list.h implementation, and makes it be
something *average*.

The Linux kernel list.h is _better_ than most stupid list implementations
that think that a head node is different from the list node. Exactly
because it very naturally supports the notion of "this structure exists in
a 'ring of entries'" where each node is 100% equivalent to any other node,
and there _is_ no head.

And your patch totally misunderstands that, and breaks it.

Nack.

		Linus

From: Linus Torvalds <torvalds@linux-foundation.org>
Newsgroups: fa.linux.kernel
Subject: Re: [PATCH RFC] struct list_node
Date: Sun, 10 Jun 2007 20:20:06 UTC
Message-ID: <fa.AkE8GwKi0Fv42u3B2VggoFLMwXs@ifi.uio.no>

On Sun, 10 Jun 2007, Linus Torvalds wrote:
>
> The Linux kernel list.h is _better_ than most stupid list implementations
> that think that a head node is different from the list node. Exactly
> because it very naturally supports the notion of "this structure exists in
> a 'ring of entries'" where each node is 100% equivalent to any other node,
> and there _is_ no head.

Btw, to extend a bit on this: there actually *is* a "list with a head"
implementation in <linux/list.h>, called "hlist".

Now, the "h" actually historically stands for "hash", but if you prefer,
you can think of it as standing for "head", and be happy.

And if you want a head, you really do want to use "hlist", since the head
is smaller than a list entry (a single pointer rather than two).

And yes, I'm sure we could change some "struct list" users to "struct
hlist" if you wanted to.

		Linus