Linux内核链表list

     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

 

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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

 

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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

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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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