mirror of
https://github.com/MintCN/linux-insides-zh.git
synced 2026-04-25 19:20:28 +08:00
mudongliang
@@ -3,13 +3,15 @@ Linux内核中的数据结构
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基数树
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--------------------------------------------------------------------------------
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As you already know linux kernel provides many different libraries and functions which implement different data structures and algorithms. In this part we will consider one of these data structures - [Radix tree](http://en.wikipedia.org/wiki/Radix_tree). There are two files which are related to `radix tree` implementation and API in the linux kernel:
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正如你所知道的 Linux 内核通过许多不同库以及函数提供各种数据结构以及算法实现。
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这个部分我们将介绍其中一个数据结构 [Radix tree](http://en.wikipedia.org/wiki/Radix_tree)。Linux 内核中有两个文件与 `radix tree` 的实现和API相关：
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* [include/linux/radix-tree.h](https://github.com/torvalds/linux/blob/master/include/linux/radix-tree.h)
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* [lib/radix-tree.c](https://github.com/torvalds/linux/blob/master/lib/radix-tree.c)
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Lets talk about what a `radix tree` is. Radix tree is a `compressed trie` where a [trie](http://en.wikipedia.org/wiki/Trie) is a data structure which implements an interface of an associative array and allows to store values as `key-value`. The keys are usually strings, but any data type can be used. A trie is different from an `n-tree` because of its nodes. Nodes of a trie do not store keys; instead, a node of a trie stores single character labels. The key which is related to a given node is derived by traversing from the root of the tree to this node. For example:
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首先说明一下什么是 `radix tree` 。Radix tree 是一种 `压缩 trie`，其中 [trie](http://en.wikipedia.org/wiki/Trie) 是一种通过保存关联数组（associative array）来提供 `关键字-值（key-value）` 存储与查找的数据结构。通常关键字是字符串，不过也可以是其他数据类型。
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trie 结构的节点与 `n-tree` 不同，其节点中并不存储关键字，取而代之的是存储单个字符标签。关键字查找时，通过从树的根开始遍历关键字相关的所有字符标签节点，直至到达最终的叶子节点。下面是个例子：
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```
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@@ -41,9 +43,9 @@ Lets talk about what a `radix tree` is. Radix tree is a `compressed trie` where
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+-----------+
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```
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So in this example, we can see the `trie` with keys, `go` and `cat`. A compressed trie or `radix tree` differs from a `trie` in that all intermediates nodes which have only one child are removed.
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这个例子中，我们可以看到 `trie` 所存储的关键字信息 `go` 与 `cat`，压缩 trie 或 `radix tree` 与 `trie` 所不同的是，所有只存在单个孩子的中间节点将被压缩。
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Radix tree in linux kernel is the data structure which maps values to the integer key. It is represented by the following structures from the file [include/linux/radix-tree.h](https://github.com/torvalds/linux/blob/master/include/linux/radix-tree.h):
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Linux 内核中的 Radix 树将值映射为整型关键字，Radix 的数据结构定义在 [include/linux/radix-tree.h](https://github.com/torvalds/linux/blob/master/include/linux/radix-tree.h) 文件中 :
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```C
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struct radix_tree_root {
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@@ -53,17 +55,18 @@ struct radix_tree_root {
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};
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```
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This structure presents the root of a radix tree and contains three fields:
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上面这个是 radix 树的 root 节点的结构体，它包括三个成员：
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* `height` - height of the tree;
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* `gfp_mask` - tells how memory allocations are to be performed;
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* `rnode` - pointer to the child node.
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* `height` - 从叶节点向上计算出的树高度。
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* `gfp_mask` - 内存分配标识。
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* `rnode` - 子节点指针。
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The first structure we will discuss is `gfp_mask`:
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这里我们先讨论的结构体成员是 `gfp_mask` :
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Low-level kernel memory allocation functions take a set of flags as - `gfp_mask`, which describes how that allocation is to be performed. These `GFP_` flags which control the allocation process can have following values: (`GF_NOIO` flag) means sleep and wait for memory, (`__GFP_HIGHMEM` flag) means high memory can be used, (`GFP_ATOMIC` flag) means the allocation process has high-priority and can't sleep etc.
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Linux 底层的内存申请接口需要提供一类标识（flag） - `gfp_mask` ，用于描述内存申请的行为。这个以 `GFP_` 前缀开头的内存申请控制标识主要包括，`GFP_NOIO` 禁止所有IO操作但允许睡眠等待内存，`__GFP_HIGHMEM` 允许申请内核的高端内存，`GFP_ATOMIC` 高优先级申请内存且操作不允许被睡眠。
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The next structure is `rnode`:
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接下来说的结构体成员是`rnode`：
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```C
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struct radix_tree_node {
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@@ -83,29 +86,32 @@ struct radix_tree_node {
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};
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```
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This structure contains information about the offset in a parent and height from the bottom, count of the child nodes and fields for accessing and freeing a node. The fields are described below:
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这个结构体中包括这几个内容，节点与父节点的偏移以及到树底端的高度，子节点的个数，节点的存储数据域，具体描述如下：
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* `path` - offset in parent & height from the bottom;
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* `count` - count of the child nodes;
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* `parent` - pointer to the parent node;
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* `private_data` - used by the user of a tree;
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* `rcu_head` - used for freeing a node;
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* `private_list` - used by the user of a tree;
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* `path` - 从叶节点
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* `count` - 子节点的个数。
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* `parent` - 父节点的指针。
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* `private_data` - 存储数据内容缓冲区。
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* `rcu_head` - 用于节点释放的RCU链表。
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* `private_list` - 存储数据。
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The two last fields of the `radix_tree_node` - `tags` and `slots` are important and interesting. Every node can contains a set of slots which are store pointers to the data. Empty slots in the linux kernel radix tree implementation store `NULL`. Radix trees in the linux kernel also supports tags which are associated with the `tags` fields in the `radix_tree_node` structure. Tags allow individual bits to be set on records which are stored in the radix tree.
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结构体 `radix_tree_node` 的最后两个成员 `tags` 与 `slots` 是非常重要且需要特别注意的。每个 Radix 树节点都可以包括一个指向存储数据指针的 slots 集合，空闲 slots 的指针指向 NULL。 Linux 内核的 Radix 树结构体中还包含用于记录节点存储状态的标签 `tags` 成员，标签通过位设置指示 Radix 树的数据存储状态。
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Now that we know about radix tree structure, it is time to look on its API.
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至此，我们了解到 radix 树的结构，接下来看一下 radix 树所提供的 API。
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Linux kernel radix tree API
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Linux 内核基数树 API
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---------------------------------------------------------------------------------
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We start from the data structure intialization. There are two ways to initialize new radix tree. The first is to use `RADIX_TREE` macro:
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我们从数据结构的初始化开始看，radix 树支持两种方式初始化。
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第一个是使用宏 `RADIX_TREE` ：
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```C
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RADIX_TREE(name, gfp_mask);
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````
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As you can see we pass the `name` parameter, so with the `RADIX_TREE` macro we can define and initialize radix tree with the given name. Implementation of the `RADIX_TREE` is easy:
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正如你看到，只需要提供 `name` 参数，就能够使用 `RADIX_TREE` 宏完成 radix 的定义以及初始化，`RADIX_TREE` 宏的实现非常简单：
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```C
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#define RADIX_TREE(name, mask) \
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@@ -118,16 +124,14 @@ As you can see we pass the `name` parameter, so with the `RADIX_TREE` macro we c
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}
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```
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At the beginning of the `RADIX_TREE` macro we define instance of the `radix_tree_root` structure with the given name and call `RADIX_TREE_INIT` macro with the given mask. The `RADIX_TREE_INIT` macro just initializes `radix_tree_root` structure with the default values and the given mask.
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The second way is to define `radix_tree_root` structure by hand and pass it with mask to the `INIT_RADIX_TREE` macro:
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`RADIX_TREE` 宏首先使用 `name` 定义了一个 `radix_tree_root` 实例并用 `RADIX_TREE_INIT` 宏带参数 `mask` 进行初始化。宏 `RADIX_TREE_INIT` 将 `radix_tree_root` 初始化为默认属性并将 gfp_mask 初始化为入参 `mask` 。
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第二种方式是手工定义 `radix_tree_root` 变量，之后再使用 `mask` 调用 `INIT_RADIX_TREE` 宏对变量进行初始化。
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```C
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struct radix_tree_root my_radix_tree;
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INIT_RADIX_TREE(my_tree, gfp_mask_for_my_radix_tree);
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```
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where:
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`INIT_RADIX_TREE` 宏定义：
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```C
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#define INIT_RADIX_TREE(root, mask) \
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@@ -137,34 +141,36 @@ do { \
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(root)->rnode = NULL; \
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} while (0)
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```
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宏 `INIT_RADIX_TREE` 所初始化的属性与 `RADIX_TREE_INIT` 一致
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makes the same initialziation with default values as it does `RADIX_TREE_INIT` macro.
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The next are two functions for the inserting and deleting records to/from a radix tree:
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接下来是 radix 树的节点插入以及删除，这两个函数：
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* `radix_tree_insert`;
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* `radix_tree_delete`.
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The first `radix_tree_insert` function takes three parameters:
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第一个函数 `radix_tree_insert` 需要三个入参：
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* root of a radix tree;
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* index key;
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* data to insert;
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* radix 树 root 节点结构
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* 索引关键字
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* 需要插入存储的数据
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The `radix_tree_delete` function takes the same set of parameters as the `radix_tree_insert`, but without data.
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第二个函数 `radix_tree_delete` 除了不需要存储数据参数外，其他与 `radix_tree_insert` 一致。
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The search in a radix tree implemented in two ways:
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radix 树的查找实现有以下几个函数：The search in a radix tree implemented in two ways:
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* `radix_tree_lookup`;
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* `radix_tree_gang_lookup`;
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* `radix_tree_lookup_slot`.
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The first `radix_tree_lookup` function takes two parameters:
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第一个函数 `radix_tree_lookup` 需要两个参数：
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* root of a radix tree;
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* index key;
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* radix 树 root 节点结构
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* 索引关键字
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This function tries to find the given key in the tree and return the record associated with this key. The second `radix_tree_gang_lookup` function have the following signature
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这个函数通过给定的关键字查找 radix 树，并返关键字所对应的结点。
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第二个函数 `radix_tree_gang_lookup` 具有以下特征：
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```C
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unsigned int radix_tree_gang_lookup(struct radix_tree_root *root,
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@@ -173,12 +179,15 @@ unsigned int radix_tree_gang_lookup(struct radix_tree_root *root,
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unsigned int max_items);
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```
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and returns number of records, sorted by the keys, starting from the first index. Number of the returned records will be not greater than `max_items` value.
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函数返回查找到记录的条目数，并根据关键字进行排序，返回的总结点数不超过入参 `max_items` 的大小。
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And the last `radix_tree_lookup_slot` function will return the slot which will contain the data.
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最后一个函数 `radix_tree_lookup_slot` 返回结点 slot 中所存储的数据。
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Links
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链接
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---------------------------------------------------------------------------------
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* [Radix tree](http://en.wikipedia.org/wiki/Radix_tree)
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* [Trie](http://en.wikipedia.org/wiki/Trie)
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71
README.md
71
README.md
@@ -1,4 +1,4 @@
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linux-insides
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Linux Insides
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===============
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一系列关于Linux内核和其内在机理的帖子。
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@@ -7,19 +7,62 @@ linux-insides
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**问题/建议**: 通过在twitter上[@0xAX](https://twitter.com/0xAX)，直接添加[issue](https://github.com/0xAX/linux-internals/issues/new)或者直接给我发[邮件](mailto:anotherworldofworld@gmail.com),请自由地向我提出任何问题或者建议。
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LICENSE
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-------------
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##翻译进度
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| 章节|译者|翻译进度|
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| ------------- |:-------------:| -----:|
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|Booting||正在进行|
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||||
|├1.1|[@xinqiu](https://github.com/xinqiu)|正在进行|
|
||||
|├1.2||未开始|
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||||
|├1.3||未开始|
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||||
|├1.4||未开始|
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||||
|└1.5||未开始|
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|Initialization||未开始|
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|Interrupts||未开始|
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|System calls||未开始|
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|Timers and time management||未开始|
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|Memory management||未开始|
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|Concepts||未开始|
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|DataStructures||正在进行|
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|├9.1|[@mudongliang](https://github.com/mudongliang)|正在进行|
|
||||
|└9.2|[Alick Guo](https://github.com/a1ickgu0)|正在进行|
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|Theory||正在进行|
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||||
|├10.1|[@mudongliang](https://github.com/mudongliang)|正在进行|
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||||
|└10.2|[@mudongliang](https://github.com/mudongliang)|已完成|
|
||||
|Misc||正在进行|
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||||
|├12.1|[@oska874](https://github.com/oska874)|已完成|
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||||
|├12.2||未开始|
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||||
|└12.3||未开始|
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||||
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##翻译认领规则
|
||||
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||||
为了避免多个译者同时翻译相同章节的情况出现， 请按照以下规则认领自己要翻译的章节：
|
||||
|
||||
* 开一个 issue ，告诉大家你想翻译哪一章或者哪一节，并且确保 issue 页面里面没有其他人在翻译相同的章节。
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||||
* 开始翻译你认领的章节。
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||||
* 完成翻译之后，关闭 issue 。
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||||
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||||
翻译前建议看 `TRANSLATION_NOTES.md` 翻译约定，有任何问题或建议也请开 issue 讨论。
|
||||
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||||
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||||
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||||
##作者
|
||||
|
||||
[@0xAX](https://twitter.com/0xAX)
|
||||
|
||||
|
||||
##贡献者
|
||||
|
||||
[@xinqiu](https://github.com/xinqiu)
|
||||
|
||||
[@oska874](https://github.com/oska874)
|
||||
|
||||
[@mudongliang](https://github.com/mudongliang)
|
||||
|
||||
[@Alick Guo](https://github.com/a1ickgu0)
|
||||
|
||||
##LICENSE
|
||||
|
||||
Licensed [BY-NC-SA Creative Commons](http://creativecommons.org/licenses/by-nc-sa/4.0/).
|
||||
|
||||
作者
|
||||
---------------
|
||||
[@0xAX](https://twitter.com/0xAX)
|
||||
|
||||
译者
|
||||
---------------
|
||||
[@xinqiu](http://xinqiu.me)
|
||||
|
||||
[@oska874](ezio_zhang@outlook.com)
|
||||
|
||||
[@mudongliang](https://github.com/mudongliang)
|
||||
|
||||
49
TRANSLATION_NOTES.md
Normal file
49
TRANSLATION_NOTES.md
Normal file
@@ -0,0 +1,49 @@
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||||
#翻译约定
|
||||
|
||||
## 基本要求
|
||||
|
||||
* 准确表述原文的意思；
|
||||
* 中文应该意思清晰且符合中文表达习惯；
|
||||
* 原文如果表达不清晰，中文应该意译，并且应根据上下文和注释进行推断并填补相应的信息；
|
||||
* 情况 `3` 不能太多；
|
||||
* 对同样短语的翻译，前后必须一致；
|
||||
* 在没有其它影响的情况下，英文“you”统一翻译为“你”。如果原文中“you”的出现过于频繁，可以在译文中适当减少“你”，或将部分“你”用“我们”替代，但应考虑如下原则：
|
||||
|
||||
* 保证句子主语明确、主谓一致。
|
||||
* “你”与“我们”的表述不必严格统一，优先考虑行文的流畅。
|
||||
* 某些可以根据上下文确定主语的场景，可以省略“你”或“我们”，但不宜滥用。
|
||||
|
||||
* 不要使用机器翻译的成果来提交，也就是说您可以使用 `Google Translate` 来帮助您理解内容，但是不能不经考虑就把其自动翻译的结果放在翻译里；
|
||||
|
||||
## 格式要求
|
||||
|
||||
### 标点的使用
|
||||
|
||||
一般的原则是：除了小括号、省略号和破折号保留不变以外，都应该使用中文(全角)标点符号。英文标点符号后方常常跟随有一个半角空格，请在翻译成中文标点符号时将其去除。另外，标点两侧不应有空格，输出、引用除外。
|
||||
|
||||
### 关于空格
|
||||
|
||||
为了美观，通常建议在中文与英文、中文与阿拉伯数字、英文与阿拉伯数字之间加入一个半角空格。如果英文、数字的前后是标点，则不需再添加空格。例如：
|
||||
|
||||
英文：Installing driver for %1
|
||||
中文：正在安装 %1 的驱动程序
|
||||
|
||||
英文：
|
||||
Parameter start_num specifies the character at which to start the search.
|
||||
The first character is character number 1. If start_num is omitted, it is
|
||||
assumed to be 1.
|
||||
中文：
|
||||
参数 start_num 指定开始搜索的字符位置。第一个字符序号为 1。如果省略 "
|
||||
"start_num，默认它为 1。"
|
||||
|
||||
不过，有时候有例如：“2013年6月5日”的视觉效果就比“2013 年 6 月 5 日”好。
|
||||
|
||||
### 其他
|
||||
|
||||
* 所有的英文人名统一不译，保留原文。
|
||||
* 章节标题只能出现中文字样；如有必要说明术语原文，在正文中第一次出现处注明，不应重复。
|
||||
|
||||
#参见
|
||||
- [Ubuntu 简体中文小组工作指南](http://wiki.ubuntu.org.cn/Ubuntu_%E7%AE%80%E4%BD%93%E4%B8%AD%E6%96%87%E5%B0%8F%E7%BB%84%E5%B7%A5%E4%BD%9C%E6%8C%87%E5%8D%97)
|
||||
- [Markdown基础](https://help.github.com/articles/markdown-basics/)
|
||||
- [Markdown 语法说明 (简体中文版)](http://wowubuntu.com/markdown/index.html)
|
||||
Reference in New Issue
Block a user