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Date: Mon, 28 Nov 2016 18:30:53 +0100
From: Silvio Fricke <silvio.fricke@...il.com>
To: linux-doc@...r.kernel.org
Cc: Jonathan Corbet <corbet@....net>,
Ming Lei <ming.lei@...onical.com>,
"Luis R . Rodriguez" <mcgrof@...nel.org>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
linux-kernel@...r.kernel.org,
Jani Nikula <jani.nikula@...ux.intel.com>,
Peter Zijlstra <peterz@...radead.org>,
Daniel Vetter <daniel@...ll.ch>,
Silvio Fricke <silvio.fricke@...il.com>
Subject: [PATCH v4 1/4] Documentation/assoc_array.txt: convert to ReST markup
... and move to Documentation/core-api folder.
Signed-off-by: Silvio Fricke <silvio.fricke@...il.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab@...pensource.com>
---
Documentation/assoc_array.txt => Documentation/core-api/assoc_array.rst | 639 ++++++++++++++++++++++++++++++++++--------------------------------------
Documentation/core-api/index.rst | 1 +-
2 files changed, 309 insertions(+), 331 deletions(-)
diff --git a/Documentation/assoc_array.txt b/Documentation/core-api/assoc_array.rst
similarity index 46%
rename from Documentation/assoc_array.txt
rename to Documentation/core-api/assoc_array.rst
index 2f2c6cd..dcda7c6 100644
--- a/Documentation/assoc_array.txt
+++ b/Documentation/core-api/assoc_array.rst
@@ -1,67 +1,46 @@
- ========================================
- GENERIC ASSOCIATIVE ARRAY IMPLEMENTATION
- ========================================
+========================================
+Generic Associative Array Implementation
+========================================
-Contents:
-
- - Overview.
-
- - The public API.
- - Edit script.
- - Operations table.
- - Manipulation functions.
- - Access functions.
- - Index key form.
-
- - Internal workings.
- - Basic internal tree layout.
- - Shortcuts.
- - Splitting and collapsing nodes.
- - Non-recursive iteration.
- - Simultaneous alteration and iteration.
-
-
-========
-OVERVIEW
+Overview
========
This associative array implementation is an object container with the following
properties:
- (1) Objects are opaque pointers. The implementation does not care where they
- point (if anywhere) or what they point to (if anything).
-
- [!] NOTE: Pointers to objects _must_ be zero in the least significant bit.
+1. Objects are opaque pointers. The implementation does not care where they
+ point (if anywhere) or what they point to (if anything).
+.. note:: Pointers to objects _must_ be zero in the least significant bit.**
- (2) Objects do not need to contain linkage blocks for use by the array. This
- permits an object to be located in multiple arrays simultaneously.
- Rather, the array is made up of metadata blocks that point to objects.
+2. Objects do not need to contain linkage blocks for use by the array. This
+ permits an object to be located in multiple arrays simultaneously.
+ Rather, the array is made up of metadata blocks that point to objects.
- (3) Objects require index keys to locate them within the array.
+3. Objects require index keys to locate them within the array.
- (4) Index keys must be unique. Inserting an object with the same key as one
- already in the array will replace the old object.
+4. Index keys must be unique. Inserting an object with the same key as one
+ already in the array will replace the old object.
- (5) Index keys can be of any length and can be of different lengths.
+5. Index keys can be of any length and can be of different lengths.
- (6) Index keys should encode the length early on, before any variation due to
- length is seen.
+6. Index keys should encode the length early on, before any variation due to
+ length is seen.
- (7) Index keys can include a hash to scatter objects throughout the array.
+7. Index keys can include a hash to scatter objects throughout the array.
- (8) The array can iterated over. The objects will not necessarily come out in
- key order.
+8. The array can iterated over. The objects will not necessarily come out in
+ key order.
- (9) The array can be iterated over whilst it is being modified, provided the
- RCU readlock is being held by the iterator. Note, however, under these
- circumstances, some objects may be seen more than once. If this is a
- problem, the iterator should lock against modification. Objects will not
- be missed, however, unless deleted.
+9. The array can be iterated over whilst it is being modified, provided the
+ RCU readlock is being held by the iterator. Note, however, under these
+ circumstances, some objects may be seen more than once. If this is a
+ problem, the iterator should lock against modification. Objects will not
+ be missed, however, unless deleted.
-(10) Objects in the array can be looked up by means of their index key.
+10. Objects in the array can be looked up by means of their index key.
-(11) Objects can be looked up whilst the array is being modified, provided the
- RCU readlock is being held by the thread doing the look up.
+11. Objects can be looked up whilst the array is being modified, provided the
+ RCU readlock is being held by the thread doing the look up.
The implementation uses a tree of 16-pointer nodes internally that are indexed
on each level by nibbles from the index key in the same manner as in a radix
@@ -71,25 +50,26 @@ pack leaf object pointers into spare space in the node rather than making an
extra branch until as such time an object needs to be added to a full node.
+The Public API
==============
-THE PUBLIC API
-==============
-The public API can be found in <linux/assoc_array.h>. The associative array is
-rooted on the following structure:
+The public API can be found in ``<linux/assoc_array.h>``. The associative
+array is rooted on the following structure::
+
+ struct assoc_array {
+ ...
+ };
- struct assoc_array {
- ...
- };
+The code is selected by enabling ``CONFIG_ASSOCIATIVE_ARRAY`` with::
-The code is selected by enabling CONFIG_ASSOCIATIVE_ARRAY.
+ ./script/config -e ASSOCIATIVE_ARRAY
-EDIT SCRIPT
+Edit Script
-----------
The insertion and deletion functions produce an 'edit script' that can later be
-applied to effect the changes without risking ENOMEM. This retains the
+applied to effect the changes without risking ``ENOMEM``. This retains the
preallocated metadata blocks that will be installed in the internal tree and
keeps track of the metadata blocks that will be removed from the tree when the
script is applied.
@@ -99,246 +79,245 @@ script has been applied so that they can be freed later. The freeing is done
after an RCU grace period has passed - thus allowing access functions to
proceed under the RCU read lock.
-The script appears as outside of the API as a pointer of the type:
+The script appears as outside of the API as a pointer of the type::
- struct assoc_array_edit;
+ struct assoc_array_edit;
There are two functions for dealing with the script:
- (1) Apply an edit script.
+1. Apply an edit script::
- void assoc_array_apply_edit(struct assoc_array_edit *edit);
+ void assoc_array_apply_edit(struct assoc_array_edit *edit);
- This will perform the edit functions, interpolating various write barriers
- to permit accesses under the RCU read lock to continue. The edit script
- will then be passed to call_rcu() to free it and any dead stuff it points
- to.
+This will perform the edit functions, interpolating various write barriers
+to permit accesses under the RCU read lock to continue. The edit script
+will then be passed to ``call_rcu()`` to free it and any dead stuff it points
+to.
- (2) Cancel an edit script.
+2. Cancel an edit script::
- void assoc_array_cancel_edit(struct assoc_array_edit *edit);
+ void assoc_array_cancel_edit(struct assoc_array_edit *edit);
- This frees the edit script and all preallocated memory immediately. If
- this was for insertion, the new object is _not_ released by this function,
- but must rather be released by the caller.
+This frees the edit script and all preallocated memory immediately. If
+this was for insertion, the new object is _not_ released by this function,
+but must rather be released by the caller.
These functions are guaranteed not to fail.
-OPERATIONS TABLE
+Operations Table
----------------
-Various functions take a table of operations:
+Various functions take a table of operations::
- struct assoc_array_ops {
- ...
- };
+ struct assoc_array_ops {
+ ...
+ };
This points to a number of methods, all of which need to be provided:
- (1) Get a chunk of index key from caller data:
+1. Get a chunk of index key from caller data::
- unsigned long (*get_key_chunk)(const void *index_key, int level);
+ unsigned long (*get_key_chunk)(const void *index_key, int level);
- This should return a chunk of caller-supplied index key starting at the
- *bit* position given by the level argument. The level argument will be a
- multiple of ASSOC_ARRAY_KEY_CHUNK_SIZE and the function should return
- ASSOC_ARRAY_KEY_CHUNK_SIZE bits. No error is possible.
+This should return a chunk of caller-supplied index key starting at the
+*bit* position given by the level argument. The level argument will be a
+multiple of ``ASSOC_ARRAY_KEY_CHUNK_SIZE`` and the function should return
+``ASSOC_ARRAY_KEY_CHUNK_SIZE bits``. No error is possible.
- (2) Get a chunk of an object's index key.
+2. Get a chunk of an object's index key::
- unsigned long (*get_object_key_chunk)(const void *object, int level);
+ unsigned long (*get_object_key_chunk)(const void *object, int level);
- As the previous function, but gets its data from an object in the array
- rather than from a caller-supplied index key.
+As the previous function, but gets its data from an object in the array
+rather than from a caller-supplied index key.
- (3) See if this is the object we're looking for.
+3. See if this is the object we're looking for::
- bool (*compare_object)(const void *object, const void *index_key);
+ bool (*compare_object)(const void *object, const void *index_key);
- Compare the object against an index key and return true if it matches and
- false if it doesn't.
+Compare the object against an index key and return ``true`` if it matches and
+``false`` if it doesn't.
- (4) Diff the index keys of two objects.
+4. Diff the index keys of two objects::
- int (*diff_objects)(const void *object, const void *index_key);
+ int (*diff_objects)(const void *object, const void *index_key);
- Return the bit position at which the index key of the specified object
- differs from the given index key or -1 if they are the same.
+Return the bit position at which the index key of the specified object
+differs from the given index key or -1 if they are the same.
- (5) Free an object.
+5. Free an object::
- void (*free_object)(void *object);
+ void (*free_object)(void *object);
- Free the specified object. Note that this may be called an RCU grace
- period after assoc_array_apply_edit() was called, so synchronize_rcu() may
- be necessary on module unloading.
+Free the specified object. Note that this may be called an RCU grace period
+after ``assoc_array_apply_edit()`` was called, so ``synchronize_rcu()`` may be
+necessary on module unloading.
-MANIPULATION FUNCTIONS
+Manipulation Functions
----------------------
There are a number of functions for manipulating an associative array:
- (1) Initialise an associative array.
+1. Initialise an associative array::
- void assoc_array_init(struct assoc_array *array);
+ void assoc_array_init(struct assoc_array *array);
- This initialises the base structure for an associative array. It can't
- fail.
+This initialises the base structure for an associative array. It can't fail.
- (2) Insert/replace an object in an associative array.
+2. Insert/replace an object in an associative array::
- struct assoc_array_edit *
- assoc_array_insert(struct assoc_array *array,
- const struct assoc_array_ops *ops,
- const void *index_key,
- void *object);
+ struct assoc_array_edit *
+ assoc_array_insert(struct assoc_array *array,
+ const struct assoc_array_ops *ops,
+ const void *index_key,
+ void *object);
- This inserts the given object into the array. Note that the least
- significant bit of the pointer must be zero as it's used to type-mark
- pointers internally.
+This inserts the given object into the array. Note that the least
+significant bit of the pointer must be zero as it's used to type-mark
+pointers internally.
- If an object already exists for that key then it will be replaced with the
- new object and the old one will be freed automatically.
+If an object already exists for that key then it will be replaced with the
+new object and the old one will be freed automatically.
- The index_key argument should hold index key information and is
- passed to the methods in the ops table when they are called.
+The ``index_key`` argument should hold index key information and is
+passed to the methods in the ops table when they are called.
- This function makes no alteration to the array itself, but rather returns
- an edit script that must be applied. -ENOMEM is returned in the case of
- an out-of-memory error.
+This function makes no alteration to the array itself, but rather returns
+an edit script that must be applied. ``-ENOMEM`` is returned in the case of
+an out-of-memory error.
- The caller should lock exclusively against other modifiers of the array.
+The caller should lock exclusively against other modifiers of the array.
- (3) Delete an object from an associative array.
+3. Delete an object from an associative array::
- struct assoc_array_edit *
- assoc_array_delete(struct assoc_array *array,
- const struct assoc_array_ops *ops,
- const void *index_key);
+ struct assoc_array_edit *
+ assoc_array_delete(struct assoc_array *array,
+ const struct assoc_array_ops *ops,
+ const void *index_key);
- This deletes an object that matches the specified data from the array.
+This deletes an object that matches the specified data from the array.
- The index_key argument should hold index key information and is
- passed to the methods in the ops table when they are called.
+The ``index_key`` argument should hold index key information and is
+passed to the methods in the ops table when they are called.
- This function makes no alteration to the array itself, but rather returns
- an edit script that must be applied. -ENOMEM is returned in the case of
- an out-of-memory error. NULL will be returned if the specified object is
- not found within the array.
+This function makes no alteration to the array itself, but rather returns
+an edit script that must be applied. ``-ENOMEM`` is returned in the case of
+an out-of-memory error. ``NULL`` will be returned if the specified object is
+not found within the array.
- The caller should lock exclusively against other modifiers of the array.
+The caller should lock exclusively against other modifiers of the array.
- (4) Delete all objects from an associative array.
+4. Delete all objects from an associative array::
- struct assoc_array_edit *
- assoc_array_clear(struct assoc_array *array,
- const struct assoc_array_ops *ops);
+ struct assoc_array_edit *
+ assoc_array_clear(struct assoc_array *array,
+ const struct assoc_array_ops *ops);
- This deletes all the objects from an associative array and leaves it
- completely empty.
+This deletes all the objects from an associative array and leaves it
+completely empty.
- This function makes no alteration to the array itself, but rather returns
- an edit script that must be applied. -ENOMEM is returned in the case of
- an out-of-memory error.
+This function makes no alteration to the array itself, but rather returns
+an edit script that must be applied. ``-ENOMEM`` is returned in the case of
+an out-of-memory error.
- The caller should lock exclusively against other modifiers of the array.
+The caller should lock exclusively against other modifiers of the array.
- (5) Destroy an associative array, deleting all objects.
+5. Destroy an associative array, deleting all objects::
- void assoc_array_destroy(struct assoc_array *array,
- const struct assoc_array_ops *ops);
+ void assoc_array_destroy(struct assoc_array *array,
+ const struct assoc_array_ops *ops);
- This destroys the contents of the associative array and leaves it
- completely empty. It is not permitted for another thread to be traversing
- the array under the RCU read lock at the same time as this function is
- destroying it as no RCU deferral is performed on memory release -
- something that would require memory to be allocated.
+This destroys the contents of the associative array and leaves it
+completely empty. It is not permitted for another thread to be traversing
+the array under the RCU read lock at the same time as this function is
+destroying it as no RCU deferral is performed on memory release -
+something that would require memory to be allocated.
- The caller should lock exclusively against other modifiers and accessors
- of the array.
+The caller should lock exclusively against other modifiers and accessors
+of the array.
- (6) Garbage collect an associative array.
+6. Garbage collect an associative array::
- int assoc_array_gc(struct assoc_array *array,
- const struct assoc_array_ops *ops,
- bool (*iterator)(void *object, void *iterator_data),
- void *iterator_data);
+ int assoc_array_gc(struct assoc_array *array,
+ const struct assoc_array_ops *ops,
+ bool (*iterator)(void *object, void *iterator_data),
+ void *iterator_data);
- This iterates over the objects in an associative array and passes each one
- to iterator(). If iterator() returns true, the object is kept. If it
- returns false, the object will be freed. If the iterator() function
- returns true, it must perform any appropriate refcount incrementing on the
- object before returning.
+This iterates over the objects in an associative array and passes each one to
+``iterator()``. If ``iterator()`` returns ``true``, the object is kept. If it
+returns ``false``, the object will be freed. If the ``iterator()`` function
+returns ``true``, it must perform any appropriate refcount incrementing on the
+object before returning.
- The internal tree will be packed down if possible as part of the iteration
- to reduce the number of nodes in it.
+The internal tree will be packed down if possible as part of the iteration
+to reduce the number of nodes in it.
- The iterator_data is passed directly to iterator() and is otherwise
- ignored by the function.
+The ``iterator_data`` is passed directly to ``iterator()`` and is otherwise
+ignored by the function.
- The function will return 0 if successful and -ENOMEM if there wasn't
- enough memory.
+The function will return ``0`` if successful and ``-ENOMEM`` if there wasn't
+enough memory.
- It is possible for other threads to iterate over or search the array under
- the RCU read lock whilst this function is in progress. The caller should
- lock exclusively against other modifiers of the array.
+It is possible for other threads to iterate over or search the array under
+the RCU read lock whilst this function is in progress. The caller should
+lock exclusively against other modifiers of the array.
-ACCESS FUNCTIONS
+Access Functions
----------------
There are two functions for accessing an associative array:
- (1) Iterate over all the objects in an associative array.
+1. Iterate over all the objects in an associative array::
- int assoc_array_iterate(const struct assoc_array *array,
- int (*iterator)(const void *object,
- void *iterator_data),
- void *iterator_data);
+ int assoc_array_iterate(const struct assoc_array *array,
+ int (*iterator)(const void *object,
+ void *iterator_data),
+ void *iterator_data);
- This passes each object in the array to the iterator callback function.
- iterator_data is private data for that function.
+This passes each object in the array to the iterator callback function.
+``iterator_data`` is private data for that function.
- This may be used on an array at the same time as the array is being
- modified, provided the RCU read lock is held. Under such circumstances,
- it is possible for the iteration function to see some objects twice. If
- this is a problem, then modification should be locked against. The
- iteration algorithm should not, however, miss any objects.
+This may be used on an array at the same time as the array is being
+modified, provided the RCU read lock is held. Under such circumstances,
+it is possible for the iteration function to see some objects twice. If
+this is a problem, then modification should be locked against. The
+iteration algorithm should not, however, miss any objects.
- The function will return 0 if no objects were in the array or else it will
- return the result of the last iterator function called. Iteration stops
- immediately if any call to the iteration function results in a non-zero
- return.
+The function will return ``0`` if no objects were in the array or else it will
+return the result of the last iterator function called. Iteration stops
+immediately if any call to the iteration function results in a non-zero
+return.
- (2) Find an object in an associative array.
+2. Find an object in an associative array::
- void *assoc_array_find(const struct assoc_array *array,
- const struct assoc_array_ops *ops,
- const void *index_key);
+ void *assoc_array_find(const struct assoc_array *array,
+ const struct assoc_array_ops *ops,
+ const void *index_key);
- This walks through the array's internal tree directly to the object
- specified by the index key..
+This walks through the array's internal tree directly to the object
+specified by the index key..
- This may be used on an array at the same time as the array is being
- modified, provided the RCU read lock is held.
+This may be used on an array at the same time as the array is being
+modified, provided the RCU read lock is held.
- The function will return the object if found (and set *_type to the object
- type) or will return NULL if the object was not found.
+The function will return the object if found (and set ``*_type`` to the object
+type) or will return ``NULL`` if the object was not found.
-INDEX KEY FORM
+Index Key Form
--------------
The index key can be of any form, but since the algorithms aren't told how long
@@ -364,8 +343,7 @@ unlikely that more than one word of any particular index key will have to be
used.
-=================
-INTERNAL WORKINGS
+Internal Workings
=================
The associative array data structure has an internal tree. This tree is
@@ -373,82 +351,80 @@ constructed of two types of metadata blocks: nodes and shortcuts.
A node is an array of slots. Each slot can contain one of four things:
- (*) A NULL pointer, indicating that the slot is empty.
-
- (*) A pointer to an object (a leaf).
-
- (*) A pointer to a node at the next level.
-
- (*) A pointer to a shortcut.
+* A NULL pointer, indicating that the slot is empty.
+* A pointer to an object (a leaf).
+* A pointer to a node at the next level.
+* A pointer to a shortcut.
-BASIC INTERNAL TREE LAYOUT
+Basic Internal Tree Layout
--------------------------
Ignoring shortcuts for the moment, the nodes form a multilevel tree. The index
key space is strictly subdivided by the nodes in the tree and nodes occur on
-fixed levels. For example:
-
- Level: 0 1 2 3
- =============== =============== =============== ===============
- NODE D
- NODE B NODE C +------>+---+
- +------>+---+ +------>+---+ | | 0 |
- NODE A | | 0 | | | 0 | | +---+
- +---+ | +---+ | +---+ | : :
- | 0 | | : : | : : | +---+
- +---+ | +---+ | +---+ | | f |
- | 1 |---+ | 3 |---+ | 7 |---+ +---+
- +---+ +---+ +---+
- : : : : | 8 |---+
- +---+ +---+ +---+ | NODE E
- | e |---+ | f | : : +------>+---+
- +---+ | +---+ +---+ | 0 |
- | f | | | f | +---+
- +---+ | +---+ : :
- | NODE F +---+
- +------>+---+ | f |
- | 0 | NODE G +---+
- +---+ +------>+---+
- : : | | 0 |
- +---+ | +---+
- | 6 |---+ : :
- +---+ +---+
- : : | f |
- +---+ +---+
- | f |
- +---+
+fixed levels. For example::
+
+ Level: 0 1 2 3
+ =============== =============== =============== ===============
+ NODE D
+ NODE B NODE C +------>+---+
+ +------>+---+ +------>+---+ | | 0 |
+ NODE A | | 0 | | | 0 | | +---+
+ +---+ | +---+ | +---+ | : :
+ | 0 | | : : | : : | +---+
+ +---+ | +---+ | +---+ | | f |
+ | 1 |---+ | 3 |---+ | 7 |---+ +---+
+ +---+ +---+ +---+
+ : : : : | 8 |---+
+ +---+ +---+ +---+ | NODE E
+ | e |---+ | f | : : +------>+---+
+ +---+ | +---+ +---+ | 0 |
+ | f | | | f | +---+
+ +---+ | +---+ : :
+ | NODE F +---+
+ +------>+---+ | f |
+ | 0 | NODE G +---+
+ +---+ +------>+---+
+ : : | | 0 |
+ +---+ | +---+
+ | 6 |---+ : :
+ +---+ +---+
+ : : | f |
+ +---+ +---+
+ | f |
+ +---+
In the above example, there are 7 nodes (A-G), each with 16 slots (0-f).
-Assuming no other meta data nodes in the tree, the key space is divided thusly:
-
- KEY PREFIX NODE
- ========== ====
- 137* D
- 138* E
- 13[0-69-f]* C
- 1[0-24-f]* B
- e6* G
- e[0-57-f]* F
- [02-df]* A
+Assuming no other meta data nodes in the tree, the key space is divided
+thusly::
+
+ KEY PREFIX NODE
+ ========== ====
+ 137* D
+ 138* E
+ 13[0-69-f]* C
+ 1[0-24-f]* B
+ e6* G
+ e[0-57-f]* F
+ [02-df]* A
So, for instance, keys with the following example index keys will be found in
-the appropriate nodes:
-
- INDEX KEY PREFIX NODE
- =============== ======= ====
- 13694892892489 13 C
- 13795289025897 137 D
- 13889dde88793 138 E
- 138bbb89003093 138 E
- 1394879524789 12 C
- 1458952489 1 B
- 9431809de993ba - A
- b4542910809cd - A
- e5284310def98 e F
- e68428974237 e6 G
- e7fffcbd443 e F
- f3842239082 - A
+the appropriate nodes::
+
+ INDEX KEY PREFIX NODE
+ =============== ======= ====
+ 13694892892489 13 C
+ 13795289025897 137 D
+ 13889dde88793 138 E
+ 138bbb89003093 138 E
+ 1394879524789 12 C
+ 1458952489 1 B
+ 9431809de993ba - A
+ b4542910809cd - A
+ e5284310def98 e F
+ e68428974237 e6 G
+ e7fffcbd443 e F
+ f3842239082 - A
To save memory, if a node can hold all the leaves in its portion of keyspace,
then the node will have all those leaves in it and will not have any metadata
@@ -462,23 +438,23 @@ metadata pointer. If the metadata pointer is there, any leaf whose key matches
the metadata key prefix must be in the subtree that the metadata pointer points
to.
-In the above example list of index keys, node A will contain:
+In the above example list of index keys, node A will contain::
- SLOT CONTENT INDEX KEY (PREFIX)
- ==== =============== ==================
- 1 PTR TO NODE B 1*
- any LEAF 9431809de993ba
- any LEAF b4542910809cd
- e PTR TO NODE F e*
- any LEAF f3842239082
+ SLOT CONTENT INDEX KEY (PREFIX)
+ ==== =============== ==================
+ 1 PTR TO NODE B 1*
+ any LEAF 9431809de993ba
+ any LEAF b4542910809cd
+ e PTR TO NODE F e*
+ any LEAF f3842239082
-and node B:
+and node B::
- 3 PTR TO NODE C 13*
- any LEAF 1458952489
+ 3 PTR TO NODE C 13*
+ any LEAF 1458952489
-SHORTCUTS
+Shortcuts
---------
Shortcuts are metadata records that jump over a piece of keyspace. A shortcut
@@ -486,12 +462,13 @@ is a replacement for a series of single-occupancy nodes ascending through the
levels. Shortcuts exist to save memory and to speed up traversal.
It is possible for the root of the tree to be a shortcut - say, for example,
-the tree contains at least 17 nodes all with key prefix '1111'. The insertion
-algorithm will insert a shortcut to skip over the '1111' keyspace in a single
-bound and get to the fourth level where these actually become different.
+the tree contains at least 17 nodes all with key prefix ``1111``. The
+insertion algorithm will insert a shortcut to skip over the ``1111`` keyspace
+in a single bound and get to the fourth level where these actually become
+different.
-SPLITTING AND COLLAPSING NODES
+Splitting And Collapsing Nodes
------------------------------
Each node has a maximum capacity of 16 leaves and metadata pointers. If the
@@ -508,7 +485,7 @@ fewer, then the subtree will be collapsed down to a single node - and this will
ripple towards the root if possible.
-NON-RECURSIVE ITERATION
+Non-Recursive Iteration
-----------------------
Each node and shortcut contains a back pointer to its parent and the number of
@@ -519,55 +496,55 @@ make sure progress is made without the need for a stack.
The backpointers, however, make simultaneous alteration and iteration tricky.
-SIMULTANEOUS ALTERATION AND ITERATION
+Simultaneous Alteration And Iteration
-------------------------------------
There are a number of cases to consider:
- (1) Simple insert/replace. This involves simply replacing a NULL or old
- matching leaf pointer with the pointer to the new leaf after a barrier.
- The metadata blocks don't change otherwise. An old leaf won't be freed
- until after the RCU grace period.
-
- (2) Simple delete. This involves just clearing an old matching leaf. The
- metadata blocks don't change otherwise. The old leaf won't be freed until
- after the RCU grace period.
-
- (3) Insertion replacing part of a subtree that we haven't yet entered. This
- may involve replacement of part of that subtree - but that won't affect
- the iteration as we won't have reached the pointer to it yet and the
- ancestry blocks are not replaced (the layout of those does not change).
-
- (4) Insertion replacing nodes that we're actively processing. This isn't a
- problem as we've passed the anchoring pointer and won't switch onto the
- new layout until we follow the back pointers - at which point we've
- already examined the leaves in the replaced node (we iterate over all the
- leaves in a node before following any of its metadata pointers).
-
- We might, however, re-see some leaves that have been split out into a new
- branch that's in a slot further along than we were at.
-
- (5) Insertion replacing nodes that we're processing a dependent branch of.
- This won't affect us until we follow the back pointers. Similar to (4).
-
- (6) Deletion collapsing a branch under us. This doesn't affect us because the
- back pointers will get us back to the parent of the new node before we
- could see the new node. The entire collapsed subtree is thrown away
- unchanged - and will still be rooted on the same slot, so we shouldn't
- process it a second time as we'll go back to slot + 1.
-
-Note:
-
- (*) Under some circumstances, we need to simultaneously change the parent
- pointer and the parent slot pointer on a node (say, for example, we
- inserted another node before it and moved it up a level). We cannot do
- this without locking against a read - so we have to replace that node too.
-
- However, when we're changing a shortcut into a node this isn't a problem
- as shortcuts only have one slot and so the parent slot number isn't used
- when traversing backwards over one. This means that it's okay to change
- the slot number first - provided suitable barriers are used to make sure
- the parent slot number is read after the back pointer.
+1. Simple insert/replace. This involves simply replacing a NULL or old
+ matching leaf pointer with the pointer to the new leaf after a barrier.
+ The metadata blocks don't change otherwise. An old leaf won't be freed
+ until after the RCU grace period.
+
+2. Simple delete. This involves just clearing an old matching leaf. The
+ metadata blocks don't change otherwise. The old leaf won't be freed until
+ after the RCU grace period.
+
+3. Insertion replacing part of a subtree that we haven't yet entered. This
+ may involve replacement of part of that subtree - but that won't affect
+ the iteration as we won't have reached the pointer to it yet and the
+ ancestry blocks are not replaced (the layout of those does not change).
+
+4. Insertion replacing nodes that we're actively processing. This isn't a
+ problem as we've passed the anchoring pointer and won't switch onto the
+ new layout until we follow the back pointers - at which point we've
+ already examined the leaves in the replaced node (we iterate over all the
+ leaves in a node before following any of its metadata pointers).
+
+ We might, however, re-see some leaves that have been split out into a new
+ branch that's in a slot further along than we were at.
+
+5. Insertion replacing nodes that we're processing a dependent branch of.
+ This won't affect us until we follow the back pointers. Similar to (4).
+
+6. Deletion collapsing a branch under us. This doesn't affect us because the
+ back pointers will get us back to the parent of the new node before we
+ could see the new node. The entire collapsed subtree is thrown away
+ unchanged - and will still be rooted on the same slot, so we shouldn't
+ process it a second time as we'll go back to slot + 1.
+
+.. note::
+
+ Under some circumstances, we need to simultaneously change the parent
+ pointer and the parent slot pointer on a node (say, for example, we
+ inserted another node before it and moved it up a level). We cannot do
+ this without locking against a read - so we have to replace that node too.
+
+ However, when we're changing a shortcut into a node this isn't a problem
+ as shortcuts only have one slot and so the parent slot number isn't used
+ when traversing backwards over one. This means that it's okay to change
+ the slot number first - provided suitable barriers are used to make sure
+ the parent slot number is read after the back pointer.
Obsolete blocks and leaves are freed up after an RCU grace period has passed,
so as long as anyone doing walking or iteration holds the RCU read lock, the
diff --git a/Documentation/core-api/index.rst b/Documentation/core-api/index.rst
index f7ef7fd..480d9a3 100644
--- a/Documentation/core-api/index.rst
+++ b/Documentation/core-api/index.rst
@@ -7,6 +7,7 @@ Kernel and driver related documentation.
.. toctree::
:maxdepth: 1
+ assoc_array
workqueue
.. only:: subproject
--
git-series 0.9.1
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