Revisit doubly linked list implementation

[rdmark]

There is a doubly linked list implementation in include/atalk/list.h ostensibly borrowed from the Linux kernel and lacking proper attribution. At a glance only a few functions are used in only a few spots: in cnid.c and the Spotlight code.

This is to look into other libraries or perhaps rewriting the essential functions.

[rdmark]

There are strong similarities to this early version of include/linux/list.h from the Linux kernel:

https://elixir.bootlin.com/linux/2.1.45/source/include/linux/list.h

[rdmark]

Even better comparison is this very first revision (April 2005) of list.h from the official kernel git mirror:

https://github.com/torvalds/linux/blob/1da177e4c3f41524e886b7f1b8a0c1fc7321cac2/include/linux/list.h

The logic is practically identical to our version, albeit with slightly different interfaces. Ours has less features too.

Discarding for now. I feel more comfortable now that the code we're using is indeed originating with the Linux kernel and can be redistributed under the GNU GPL v2

[rdmark]

Going even further back, this June 2002 revision is almost entirely identical.

https://github.com/tbodt/linux-history/blob/b9a78e5991e18eb4c5f93d2d58e19f1708528dae/include/linux/list.h

[rdmark]

For future consideration: util-linux has a mostly compatible reimplementation which has clearer attribution, and seeing active development. This could be an option for forking.

https://github.com/util-linux/util-linux/blob/master/include/list.h