docs: networking: convert fib_trie.txt to ReST

- add SPDX header;
- adjust title markup;
- adjust identation, whitespaces and blank lines;
- add to networking/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 0 insertions, 145 deletions

diff --git a/Documentation/networking/fib_trie.txt b/Documentation/networking/fib_trie.txt
deleted file mode 100644
index fe719388518b..000000000000
--- a/Documentation/networking/fib_trie.txt
+++ /dev/null
@@ -1,145 +0,0 @@
-			LC-trie implementation notes.
-
-Node types
-----------
-leaf 
-	An end node with data. This has a copy of the relevant key, along
-	with 'hlist' with routing table entries sorted by prefix length.
-	See struct leaf and struct leaf_info.
-
-trie node or tnode
-	An internal node, holding an array of child (leaf or tnode) pointers,
-	indexed	through a subset of the key. See Level Compression.
-
-A few concepts explained
-------------------------
-Bits (tnode) 
-	The number of bits in the key segment used for indexing into the
-	child array - the "child index". See Level Compression.
-
-Pos (tnode)
-	The position (in the key) of the key segment used for indexing into
-	the child array. See Path Compression.
-
-Path Compression / skipped bits
-	Any given tnode is linked to from the child array of its parent, using
-	a segment of the key specified by the parent's "pos" and "bits" 
-	In certain cases, this tnode's own "pos" will not be immediately
-	adjacent to the parent (pos+bits), but there will be some bits
-	in the key skipped over because they represent a single path with no
-	deviations. These "skipped bits" constitute Path Compression.
-	Note that the search algorithm will simply skip over these bits when
-	searching, making it necessary to save the keys in the leaves to
-	verify that they actually do match the key we are searching for.
-
-Level Compression / child arrays
-	the trie is kept level balanced moving, under certain conditions, the
-	children of a full child (see "full_children") up one level, so that
-	instead of a pure binary tree, each internal node ("tnode") may
-	contain an arbitrarily large array of links to several children.
-	Conversely, a tnode with a mostly empty	child array (see empty_children)
-	may be "halved", having some of its children moved downwards one level,
-	in order to avoid ever-increasing child arrays.
-
-empty_children
-	the number of positions in the child array of a given tnode that are
-	NULL.
-
-full_children
-	the number of children of a given tnode that aren't path compressed.
-	(in other words, they aren't NULL or leaves and their "pos" is equal
-	to this	tnode's "pos"+"bits").
-
-	(The word "full" here is used more in the sense of "complete" than
-	as the opposite of "empty", which might be a tad confusing.)
-
-Comments
----------
-
-We have tried to keep the structure of the code as close to fib_hash as 
-possible to allow verification and help up reviewing. 
-
-fib_find_node()
-	A good start for understanding this code. This function implements a
-	straightforward trie lookup.
-
-fib_insert_node()
-	Inserts a new leaf node in the trie. This is bit more complicated than
-	fib_find_node(). Inserting a new node means we might have to run the
-	level compression algorithm on part of the trie.
-
-trie_leaf_remove()
-	Looks up a key, deletes it and runs the level compression algorithm.
-
-trie_rebalance()
-	The key function for the dynamic trie after any change in the trie
-	it is run to optimize and reorganize. It will walk the trie upwards
-	towards the root from a given tnode, doing a resize() at each step
-	to implement level compression.
-
-resize()
-	Analyzes a tnode and optimizes the child array size by either inflating
-	or shrinking it repeatedly until it fulfills the criteria for optimal
-	level compression. This part follows the original paper pretty closely
-	and there may be some room for experimentation here.
-
-inflate()
-	Doubles the size of the child array within a tnode. Used by resize().
-
-halve()
-	Halves the size of the child array within a tnode - the inverse of
-	inflate(). Used by resize();
-
-fn_trie_insert(), fn_trie_delete(), fn_trie_select_default()
-	The route manipulation functions. Should conform pretty closely to the
-	corresponding functions in fib_hash.
-
-fn_trie_flush()
-	This walks the full trie (using nextleaf()) and searches for empty
-	leaves which have to be removed.
-
-fn_trie_dump()
-	Dumps the routing table ordered by prefix length. This is somewhat
-	slower than the corresponding fib_hash function, as we have to walk the
-	entire trie for each prefix length. In comparison, fib_hash is organized
-	as one "zone"/hash per prefix length.
-
-Locking
--------
-
-fib_lock is used for an RW-lock in the same way that this is done in fib_hash.
-However, the functions are somewhat separated for other possible locking
-scenarios. It might conceivably be possible to run trie_rebalance via RCU
-to avoid read_lock in the fn_trie_lookup() function.
-
-Main lookup mechanism
----------------------
-fn_trie_lookup() is the main lookup function.
-
-The lookup is in its simplest form just like fib_find_node(). We descend the
-trie, key segment by key segment, until we find a leaf. check_leaf() does
-the fib_semantic_match in the leaf's sorted prefix hlist.
-
-If we find a match, we are done.
-
-If we don't find a match, we enter prefix matching mode. The prefix length,
-starting out at the same as the key length, is reduced one step at a time,
-and we backtrack upwards through the trie trying to find a longest matching
-prefix. The goal is always to reach a leaf and get a positive result from the
-fib_semantic_match mechanism.
-
-Inside each tnode, the search for longest matching prefix consists of searching
-through the child array, chopping off (zeroing) the least significant "1" of
-the child index until we find a match or the child index consists of nothing but
-zeros.
-
-At this point we backtrack (t->stats.backtrack++) up the trie, continuing to
-chop off part of the key in order to find the longest matching prefix.
-
-At this point we will repeatedly descend subtries to look for a match, and there
-are some optimizations available that can provide us with "shortcuts" to avoid
-descending into dead ends. Look for "HL_OPTIMIZE" sections in the code.
-
-To alleviate any doubts about the correctness of the route selection process,
-a new netlink operation has been added. Look for NETLINK_FIB_LOOKUP, which
-gives userland access to fib_lookup().