Linux内核链表list_head扩展---klist
Linux内核链表list_head扩展---klist
看SPI驱动核心模块时，看到用到很多klist，之前没多深入理解，现在来一步步分析源码。klist是对list_head的扩展，实现代码很少。内核代码：
include/linux/klist.h
lib/klist.c
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先要有一点点预备知识——list_head
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先看看头文件如何定义klist，以及一些基本操作方法接口。
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klist头文件 /* 头文件 */
1/*
2 * klist.h - Some generic list helpers, extending struct list_head a bit.
3 *
4 * Implementations are found in lib/klist.c
5 *
6 *
7 * Copyright (C) 2005 Patrick Mochel
8 *
9 * This file is rleased under the GPL v2.
10 */
11
12#ifndef _LINUX_KLIST_H
13#define _LINUX_KLIST_H
14
/* 自旋锁，这个过几天认真看下实现，具体作用就是多处理器的临界操作锁
* 对于嵌入式单处理器比较少用到
*/
15#include <linux/spinlock.h>
/* 这个是内核引用次数的原子变量定义和原子操作
* 操作接口就是原子变量的增加get、减少put，以此实现内核对象引用次数操作
*/
16#include <linux/kref.h>
/* 内核链表list_head */
17#include <linux/list.h>
18
/* 先声明klist_node节点，在后面定义 */
19struct klist_node;
/* klist结构体定义 */
20struct klist {
/* klist操作自旋锁 */
21 spinlock_t k_lock;
/* 内核链表 */
22 struct list_head k_list;
/* 获取klist_node节点方法 */
23 void (*get)(struct klist_node *);
/* 添加klist_node节点方法 */
24 void (*put)(struct klist_node *);
25} __attribute__ ((aligned (sizeof(void *))));/* 按指针大小对齐 */
26
/* 定义klist链表初始化宏
* 名字初始化锁、链表、get、put方法
*/
27#define KLIST_INIT(_name, _get, _put) \
/* 初始化为解锁状态 */
28 { .k_lock = __SPIN_LOCK_UNLOCKED(_name.k_lock), \
/* 初始化链表 */
29 .k_list = LIST_HEAD_INIT(_name.k_list), \
/* get方法 */
30 .get = _get, \
/* put方法 */
31 .put = _put, }
32
/* 定义并初始化链表 */
33#define DEFINE_KLIST(_name, _get, _put) \
34 struct klist _name = KLIST_INIT(_name, _get, _put)
35
/* klist初始化接口，在klist.c里具体分析 */
36extern void klist_init(struct klist *k, void (*get)(struct klist_node *),
37 void (*put)(struct klist_node *));
38
/* 节点结构体 */
39struct klist_node {
40 void *n_klist; /* never access directly */
/* 节点链表入口 */
41 struct list_head n_node;
/* 引用次数的一个原子变量 */
42 struct kref n_ref;
43};
44
/* 下面是链表操作方法声明，在klist.c具体分析 */
45extern void klist_add_tail(struct klist_node *n, struct klist *k);
46extern void klist_add_head(struct klist_node *n, struct klist *k);
47extern void klist_add_after(struct klist_node *n, struct klist_node *pos);
48extern void klist_add_before(struct klist_node *n, struct klist_node *pos);
49
50extern void klist_del(struct klist_node *n);
51extern void klist_remove(struct klist_node *n);
52
53extern int klist_node_attached(struct klist_node *n);
54
55
/* klist迭代器和操作方法，关于迭代器比较难理解，先看klist.c再说 */
56struct klist_iter {
57 struct klist *i_klist;
58 struct klist_node *i_cur;
59};
60
61
62extern void klist_iter_init(struct klist *k, struct klist_iter *i);
63extern void klist_iter_init_node(struct klist *k, struct klist_iter *i,
64 struct klist_node *n);
65extern void klist_iter_exit(struct klist_iter *i);
66extern struct klist_node *klist_next(struct klist_iter *i);
67
68#endif
69----------------------
klist实现代码 1/*
2 * klist.c - Routines for manipulating klists.
3 *
4 * Copyright (C) 2005 Patrick Mochel
5 *
6 * This file is released under the GPL v2.
7 *
8 * This klist interface provides a couple of structures that wrap around
9 * struct list_head to provide explicit list "head" (struct klist) and list
10 * "node" (struct klist_node) objects. For struct klist, a spinlock is
11 * included that protects access to the actual list itself. struct
12 * klist_node provides a pointer to the klist that owns it and a kref
13 * reference count that indicates the number of current users of that node
14 * in the list.
15 *
16 * The entire point is to provide an interface for iterating over a list
17 * that is safe and allows for modification of the list during the
18 * iteration (e.g. insertion and removal), including modification of the
19 * current node on the list.
20 *
21 * It works using a 3rd object type - struct klist_iter - that is declared
22 * and initialized before an iteration. klist_next() is used to acquire the
23 * next element in the list. It returns NULL if there are no more items.
24 * Internally, that routine takes the klist's lock, decrements the
25 * reference count of the previous klist_node and increments the count of
26 * the next klist_node. It then drops the lock and returns.
27 *
28 * There are primitives for adding and removing nodes to/from a klist.
29 * When deleting, klist_del() will simply decrement the reference count.
30 * Only when the count goes to 0 is the node removed from the list.
31 * klist_remove() will try to delete the node from the list and block until
32 * it is actually removed. This is useful for objects (like devices) that
33 * have been removed from the system and must be freed (but must wait until
34 * all accessors have finished).
35 */
36
37#include <linux/klist.h>
38#include <linux/module.h>
39#include <linux/sched.h>
40
/* 下面定义一些节点操作方法，先看下去，再来理解这些操作真正作用 */
41/*
42 * Use the lowest bit of n_klist to mark deleted nodes and exclude
43 * dead ones from iteration.
44 */
45#define KNODE_DEAD 1LU
46#define KNODE_KLIST_MASK ~KNODE_DEAD
47
/* 由节点获取链表头 */
48static struct klist *knode_klist(struct klist_node *knode)
49{
50 return (struct klist *)
51 ((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
52}
53
/* 判断节点“死了” */
54static bool knode_dead(struct klist_node *knode)
55{
56 return (unsigned long)knode->n_klist & KNODE_DEAD;
57}
58
/* 设置节点的链表 */
59static void knode_set_klist(struct klist_node *knode, struct klist *klist)
60{
61 knode->n_klist = klist;
62 /* no knode deserves to start its life dead */
/* 没有节点刚开始就是“死的” */
63 WARN_ON(knode_dead(knode));
64}
65
/* “杀死”节点 */
66static void knode_kill(struct klist_node *knode)
67{
68 /* and no knode should die twice ever either, see we're very humane */
/* 没有节点能“死”两次，瞧我们多人性化 */
69 WARN_ON(knode_dead(knode));
70 *(unsigned long *)&knode->n_klist |= KNODE_DEAD;
71}
72
73/**
74 * klist_init - Initialize a klist structure.
75 * @k: The klist we're initializing.
76 * @get: The get function for the embedding object (NULL if none)
77 * @put: The put function for the embedding object (NULL if none)
78 *
79 * Initialises the klist structure. If the klist_node structures are
80 * going to be embedded in refcounted objects (necessary for safe
81 * deletion) then the get/put arguments are used to initialise
82 * functions that take and release references on the embedding
83 * objects.
84 */
/* klist初始化接口
* get/put方法用来操作klist_node
*/
85void klist_init(struct klist *k, void (*get)(struct klist_node *),
86 void (*put)(struct klist_node *))
87{
88 INIT_LIST_HEAD(&k->k_list);
89 spin_lock_init(&k->k_lock);
90 k->get = get;
91 k->put = put;
92}
93EXPORT_SYMBOL_GPL(klist_init);
94
/* 将节点加入到链表头 */
95static void add_head(struct klist *k, struct klist_node *n)
96{
97 spin_lock(&k->k_lock);
98 list_add(&n->n_node, &k->k_list);
99 spin_unlock(&k->k_lock);
100}
101
/* 将节点加入到链表尾 */
102static void add_tail(struct klist *k, struct klist_node *n)
103{
104 spin_lock(&k->k_lock);
105 list_add_tail(&n->n_node, &k->k_list);
106 spin_unlock(&k->k_lock);
107}
108
/* 节点初始化
* 包括初始化链表、引用计数、设置指向klist
*/
109static void klist_node_init(struct klist *k, struct klist_node *n)
110{
111 INIT_LIST_HEAD(&n->n_node);
112 kref_init(&n->n_ref);
113 knode_set_klist(n, k);
/* 如果klist的get方法存在，则调用获取节点 */
114 if (k->get)
115 k->get(n);
116}
117
118/**
119 * klist_add_head - Initialize a klist_node and add it to front.
120 * @n: node we're adding.
121 * @k: klist it's going on.
122 */
/* 将节点n初始化并加入到klist的头 */
123void klist_add_head(struct klist_node *n, struct klist *k)
124{
125 klist_node_init(k, n);
126 add_head(k, n);
127}
128EXPORT_SYMBOL_GPL(klist_add_head);
129
130/**
131 * klist_add_tail - Initialize a klist_node and add it to back.
132 * @n: node we're adding.
133 * @k: klist it's going on.
134 */
/* 将节点n初始化并加入到klist的尾 */
135void klist_add_tail(struct klist_node *n, struct klist *k)
136{
137 klist_node_init(k, n);
138 add_tail(k, n);
139}
140EXPORT_SYMBOL_GPL(klist_add_tail);
141
142/**
143 * klist_add_after - Init a klist_node and add it after an existing node
144 * @n: node we're adding.
145 * @pos: node to put @n after
146 */
/* 在节点pos后面插入节点n */
147void klist_add_after(struct klist_node *n, struct klist_node *pos)
148{
149 struct klist *k = knode_klist(pos);
150
151 klist_node_init(k, n);
152 spin_lock(&k->k_lock);
153 list_add(&n->n_node, &pos->n_node);
154 spin_unlock(&k->k_lock);
155}
156EXPORT_SYMBOL_GPL(klist_add_after);
157
158/**
159 * klist_add_before - Init a klist_node and add it before an existing node
160 * @n: node we're adding.
161 * @pos: node to put @n after
162 */
/* 在节点pos前面插入节点n */
163void klist_add_before(struct klist_node *n, struct klist_node *pos)
164{
165 struct klist *k = knode_klist(pos);
166
167 klist_node_init(k, n);
168 spin_lock(&k->k_lock);
169 list_add_tail(&n->n_node, &pos->n_node);
170 spin_unlock(&k->k_lock);
171}
172EXPORT_SYMBOL_GPL(klist_add_before);
173
/* 等待者结构体，用于删除节点，删除完成唤醒进程 */
174struct klist_waiter {
175 struct list_head list;
176 struct klist_node *node;
177 struct task_struct *process;
178 int woken;
179};
180
/* 定义并初始化klist节点移除自旋锁 */
181static DEFINE_SPINLOCK(klist_remove_lock);
/* 定义一个等待器的链表 */
182static LIST_HEAD(klist_remove_waiters);
183
184static void klist_release(struct kref *kref)
185{
186 struct klist_waiter *waiter, *tmp;
187 struct klist_node *n = container_of(kref, struct klist_node, n_ref);
188
189 WARN_ON(!knode_dead(n));
/* 删除链表中的节点入口 */
190 list_del(&n->n_node);
191 spin_lock(&klist_remove_lock);
/* 内核链表操作宏include/linux/list.h，遍历klist节点移除等待链表 */
192 list_for_each_entry_safe(waiter, tmp, &klist_remove_waiters, list) {
/* 是要删除链表节点的等待器 */
193 if (waiter->node != n)
194 continue;
195
/* 等待者唤醒标志 */
196 waiter->woken = 1;
197 mb();
/* 唤醒等待进程 */
198 wake_up_process(waiter->process);
/* 删除链表入口 */
199 list_del(&waiter->list);
200 }
201 spin_unlock(&klist_remove_lock);
/* 设置节点n指向的klist为空 */
202 knode_set_klist(n, NULL);
203}
204
/* 减引用次数并删除节点 */
205static int klist_dec_and_del(struct klist_node *n)
206{
/* n->nref减引用次数，若引用次数减完不为0，调用klist_release清除节点对象，返回1；为0，则返回0 */
207 return kref_put(&n->n_ref, klist_release);
208}
209
/* 带锁操作的节点删除，不判断是否成功，减引用次数 */
210static void klist_put(struct klist_node *n, bool kill)
211{
/* 获取节点的put方法 */
212 struct klist *k = knode_klist(n);
213 void (*put)(struct klist_node *) = k->put;
214
215 spin_lock(&k->k_lock);
/* “需要杀死节点” = = */
216 if (kill)
217 knode_kill(n);
/* 节点对象引用次数为0了，则不需要调用put方法 */
218 if (!klist_dec_and_del(n))
219 put = NULL;
220 spin_unlock(&k->k_lock);
/* 调用put方法 */
221 if (put)
222 put(n);
223}
224
225/**
226 * klist_del - Decrement the reference count of node and try to remove.
227 * @n: node we're deleting.
228 */
/* 删除节点“杀死死节点 */
229void klist_del(struct klist_node *n)
230{
231 klist_put(n, true);
232}
233EXPORT_SYMBOL_GPL(klist_del);
234
235/**
236 * klist_remove - Decrement the refcount of node and wait for it to go away.
237 * @n: node we're removing.
238 */
239void klist_remove(struct klist_node *n)
240{
/* 定义一个等待者，并加入等待者加入移除等待者链表 */
241 struct klist_waiter waiter;
242
243 waiter.node = n;
244 waiter.process = current;
245 waiter.woken = 0;
246 spin_lock(&klist_remove_lock);
247 list_add(&waiter.list, &klist_remove_waiters);
248 spin_unlock(&klist_remove_lock);
249
/* 清除节点，并设置等待者 */
250 klist_del(n);
251
252 for (;;) {
/* 设置进程状态不可中断，等待 */
253 set_current_state(TASK_UNINTERRUPTIBLE);
/* 节点被删除，进程被唤醒 */
254 if (waiter.woken)
255 break;
/* 内核调度器 */
256 schedule();
257 }
/* 设置当前进程状态为运行 */
258 __set_current_state(TASK_RUNNING);
259}
260EXPORT_SYMBOL_GPL(klist_remove);
261
262/**
263 * klist_node_attached - Say whether a node is bound to a list or not.
264 * @n: Node that we're testing.
265 */
/* 判断节点是不是链表边界 */
266int klist_node_attached(struct klist_node *n)
267{
268 return (n->n_klist != NULL);
269}
270EXPORT_SYMBOL_GPL(klist_node_attached);
271
272/**
273 * klist_iter_init_node - Initialize a klist_iter structure.
274 * @k: klist we're iterating.
275 * @i: klist_iter we're filling.
276 * @n: node to start with.
277 *
278 * Similar to klist_iter_init(), but starts the action off with @n,
279 * instead of with the list head.
280 */
/* 初始化迭代器节点，使用链表节点n */
281void klist_iter_init_node(struct klist *k, struct klist_iter *i,
282 struct klist_node *n)
283{
284 i->i_klist = k;
285 i->i_cur = n;
286 if (n)
287 kref_get(&n->n_ref);
288}
289EXPORT_SYMBOL_GPL(klist_iter_init_node);
290
291/**
292 * klist_iter_init - Iniitalize a klist_iter structure.
293 * @k: klist we're iterating.
294 * @i: klist_iter structure we're filling.
295 *
296 * Similar to klist_iter_init_node(), but start with the list head.
297 */
/* 初始化迭代器节点，使用链表头 */
298void klist_iter_init(struct klist *k, struct klist_iter *i)
299{
300 klist_iter_init_node(k, i, NULL);
301}
302EXPORT_SYMBOL_GPL(klist_iter_init);
303
304/**
305 * klist_iter_exit - Finish a list iteration.
306 * @i: Iterator structure.
307 *
308 * Must be called when done iterating over list, as it decrements the
309 * refcount of the current node. Necessary in case iteration exited before
310 * the end of the list was reached, and always good form.
311 */
/* 结束链表迭代，必须在结束迭代链表时调用 */
312void klist_iter_exit(struct klist_iter *i)
313{
314 if (i->i_cur) {
315 klist_put(i->i_cur, false);
316 i->i_cur = NULL;
317 }
318}
319EXPORT_SYMBOL_GPL(klist_iter_exit);
320
/* 由链表入口获取节点 */
321static struct klist_node *to_klist_node(struct list_head *n)
322{
323 return container_of(n, struct klist_node, n_node);
324}
325
326/**
327 * klist_next - Ante up next node in list.
328 * @i: Iterator structure.
329 *
330 * First grab list lock. Decrement the reference count of the previous
331 * node, if there was one. Grab the next node, increment its reference
332 * count, drop the lock, and return that next node.
333 */
/* “预下”链表中下一节点 */
334struct klist_node *klist_next(struct klist_iter *i)
335{
336 void (*put)(struct klist_node *) = i->i_klist->put;
337 struct klist_node *last = i->i_cur;
338 struct klist_node *next;
339
/* 抢占锁 */
340 spin_lock(&i->i_klist->k_lock);
341
/* 获取下一节点 */
342 if (last) {
343 next = to_klist_node(last->n_node.next);
/* 减上一节点引用次数 */
344 if (!klist_dec_and_del(last))
345 put = NULL;
346 } else
347 next = to_klist_node(i->i_klist->k_list.next);
348
349 i->i_cur = NULL;
/* 链表中有节点“没死”，增加引用次数 */
350 while (next != to_klist_node(&i->i_klist->k_list)) {
351 if (likely(!knode_dead(next))) {
352 kref_get(&next->n_ref);
353 i->i_cur = next;
354 break;
355 }
356 next = to_klist_node(next->n_node.next);
357 }
358
/* 丢弃锁 */
359 spin_unlock(&i->i_klist->k_lock);
360
361 if (put && last)
362 put(last);
363 return i->i_cur;
364}
365EXPORT_SYMBOL_GPL(klist_next);
366----------------------
总结：
按面向对象的思想
klist是一个链表操作类，klist->k_list是链表入口，get/put是节点操作的方法。
knode是链表节点，knode->n_klist包括节点状态、链表入口， kref节点引用次数， n_node是节点链表入口
klist_iter是迭代器，是作为klist链表中查找特定对象的辅助结构体。查找特定的n_node
----------------------
结合内核驱动模型说明下klist的用法，实现代码在/drivers/base/core.c。
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klist的应用1178/**
1179 * device_for_each_child - device child iterator.
1180 * @parent: parent struct device.
1181 * @data: data for the callback.
1182 * @fn: function to be called for each device.
1183 *
1184 * Iterate over @parent's child devices, and call @fn for each,
1185 * passing it @data.
1186 *
1187 * We check the return of @fn each time. If it returns anything
1188 * other than 0, we break out and return that value.
1189 */
1190int device_for_each_child(struct device *parent, void *data,
1191 int (*fn)(struct device *dev, void *data))
1192{
1193 struct klist_iter i;
1194 struct device *child;
1195 int error = 0;
1196
1197 if (!parent->p)
1198 return 0;
1199
/* 用链表头初始化迭代器 */
1200 klist_iter_init(&parent->p->klist_children, &i);
/* 使用迭代器的方法查找下一个设备 */
1201 while ((child = next_device(&i)) && !error)
1202 error = fn(child, data);
/* 结束迭代必须调用 */
1203 klist_iter_exit(&i);
1204 return error;
1205}
/*-------------------------------------------------------------------------------*/
/* 内核驱动中用于查找下一设备 */
1122static struct device *next_device(struct klist_iter *i)
1123{
/* 使用迭代查找下一链表节点 */
1124 struct klist_node *n = klist_next(i);
1125 struct device *dev = NULL;
1126 struct device_private *p;
1127
1128 if (n) {
/* 根据节点入口获取该节点上的设备 */
1129 p = to_device_private_parent(n);
1130 dev = p->device;
1131 }
1132 return dev;
1133}
/*-------------------------------------------------------------------------------*/
/* 其中device_private是设备私有数据结构，一下代码不难看出
* 想要由链表节点迭代查找设备非常容易
*/
66/**
67 * struct device_private - structure to hold the private to the driver core portions of the device structure.
68 *
69 * @klist_children - klist containing all children of this device
70 * @knode_parent - node in sibling list
71 * @knode_driver - node in driver list
72 * @knode_bus - node in bus list
73 * @driver_data - private pointer for driver specific info. Will turn into a
74 * list soon.
75 * @device - pointer back to the struct class that this structure is
76 * associated with.
77 *
78 * Nothing outside of the driver core should ever touch these fields.
79 */
80struct device_private {
81 struct klist klist_children;
82 struct klist_node knode_parent;
83 struct klist_node knode_driver;
84 struct klist_node knode_bus;
85 void *driver_data;
86 struct device *device;
87};
88#define to_device_private_parent(obj) \
89 container_of(obj, struct device_private, knode_parent)
90#define to_device_private_driver(obj) \
91 container_of(obj, struct device_private, knode_driver)
92#define to_device_private_bus(obj) \
93 container_of(obj, struct device_private, knode_bus)
94
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