对 list.h 的分析总结-步步更新
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- 对 list.h 的一点点分析总结：
首先上代码：
#ifndef __LIST_H
#define __LIST_H
/* This file is from Linux Kernel (include/linux/list.h)
* and modified by simply removing hardware prefetching of list items.
* Here by copyright, credits attributed to wherever they belong.
* Kulesh Shanmugasundaram (kulesh [squiggly] isis.poly.edu)
*/
/*
* Simple doubly linked list implementation.
*
* Some of the internal functions ("__xxx") are useful when
* manipulating whole lists rather than single entries, as
* sometimes we already know the next/prev entries and we can
* generate better code by using them directly rather than
* using the generic single-entry routines.
*/
struct list_head {
struct list_head *next, *prev;
};
#define LIST_HEAD_INIT(name) { &(name), &(name) }
#define LIST_HEAD(name) \
struct list_head name = LIST_HEAD_INIT(name)
#define INIT_LIST_HEAD(ptr) do { \
(ptr)->next = (ptr); (ptr)->prev = (ptr); \
} while (0)
/*
* Insert a new entry between two known consecutive entries.
*
* This is only for internal list manipulation where we know
* the prev/next entries already!
*/
static inline void __list_add(struct list_head *new,
struct list_head *prev,
struct list_head *next)
{
next->prev = new;
new->next = next;
new->prev = prev;
prev->next = new;
}
/**
* list_add - add a new entry
* @new: new entry to be added
* @head: list head to add it after
*
* Insert a new entry after the specified head.
* This is good for implementing stacks.
*/
static inline void list_add(struct list_head *new, struct list_head *head)
{
__list_add(new, head, head->next);
}
/**
* list_add_tail - add a new entry
* @new: new entry to be added
* @head: list head to add it before
*
* Insert a new entry before the specified head.
* This is useful for implementing queues.
*/
static inline void list_add_tail(struct list_head *new, struct list_head *head)
{
__list_add(new, head->prev, head);
}
/*
* Delete a list entry by making the prev/next entries
* point to each other.
*
* This is only for internal list manipulation where we know
* the prev/next entries already!
*/
static inline void __list_del(struct list_head *prev, struct list_head *next)
{
next->prev = prev;
prev->next = next;
}
/**
* list_del - deletes entry from list.
* @entry: the element to delete from the list.
* Note: list_empty on entry does not return true after this, the entry is in an undefined state.
*/
static inline void list_del(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
entry->next = (void *) 0;
entry->prev = (void *) 0;
}
/**
* list_del_init - deletes entry from list and reinitialize it.
* @entry: the element to delete from the list.
*/
static inline void list_del_init(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
INIT_LIST_HEAD(entry);
}
/**
* list_move - delete from one list and add as another's head
* @list: the entry to move
* @head: the head that will precede our entry
*/
static inline void list_move(struct list_head *list, struct list_head *head)
{
__list_del(list->prev, list->next);
list_add(list, head);
}
/**
* list_move_tail - delete from one list and add as another's tail
* @list: the entry to move
* @head: the head that will follow our entry
*/
static inline void list_move_tail(struct list_head *list,
struct list_head *head)
{
__list_del(list->prev, list->next);
list_add_tail(list, head);
}
/**
* list_empty - tests whether a list is empty
* @head: the list to test.
*/
static inline int list_empty(struct list_head *head)
{
return head->next == head;
}
static inline void __list_splice(struct list_head *list,
struct list_head *head)
{
struct list_head *first = list->next;
struct list_head *last = list->prev;
struct list_head *at = head->next;
first->prev = head;
head->next = first;
last->next = at;
at->prev = last;
}
/**
* list_splice - join two lists
* @list: the new list to add.
* @head: the place to add it in the first list.
*/
static inline void list_splice(struct list_head *list, struct list_head *head)
{
if (!list_empty(list))
__list_splice(list, head);
}
/**
* list_splice_init - join two lists and reinitialise the emptied list.
* @list: the new list to add.
* @head: the place to add it in the first list.
*
* The list at @list is reinitialised
*/
static inline void list_splice_init(struct list_head *list,
struct list_head *head)
{
if (!list_empty(list)) {
__list_splice(list, head);
INIT_LIST_HEAD(list);
}
}
/**
* list_entry - get the struct for this entry
* @ptr: the &struct list_head pointer.
* @type: the type of the struct this is embedded in.
* @member: the name of the list_struct within the struct.
*/
#define list_entry(ptr, type, member) \
((type *)((char *)(ptr)-(unsigned long)(&((type *)0)->member)))
/**
* list_for_each - iterate over a list
* @pos: the &struct list_head to use as a loop counter.
* @head: the head for your list.
*/
#define list_for_each(pos, head) \
for (pos = (head)->next; pos != (head); \
pos = pos->next)
/**
* list_for_each_prev - iterate over a list backwards
* @pos: the &struct list_head to use as a loop counter.
* @head: the head for your list.
*/
#define list_for_each_prev(pos, head) \
for (pos = (head)->prev; pos != (head); \
pos = pos->prev)
/**
* list_for_each_safe - iterate over a list safe against removal of list entry
* @pos: the &struct list_head to use as a loop counter.
* @n: another &struct list_head to use as temporary storage
* @head: the head for your list.
*/
#define list_for_each_safe(pos, n, head) \
for (pos = (head)->next, n = pos->next; pos != (head); \
pos = n, n = pos->next)
/**
* list_for_each_entry - iterate over list of given type
* @pos: the type * to use as a loop counter.
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry(pos, head, member) \
for (pos = list_entry((head)->next, typeof(*pos), member); \
&pos->member != (head); \
pos = list_entry(pos->member.next, typeof(*pos), member))
/**
* list_for_each_entry_safe - iterate over list of given type safe against removal of list entry
* @pos: the type * to use as a loop counter.
* @n: another type * to use as temporary storage
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry_safe(pos, n, head, member) \
for (pos = list_entry((head)->next, typeof(*pos), member), \
n = list_entry(pos->member.next, typeof(*pos), member); \
&pos->member != (head); \
pos = n, n = list_entry(n->member.next, typeof(*n), member))
#endif
- LIST_HEAD_INIT(name) 这个带参数的宏定义是用来给某个具体的 struct list_head 类型双向链表头变量进行初始化。
- LIST_HEAD(name) 是用来直接声明并定义一个 struct list_head 类型的变量，变量名为该宏的参数 name
- INIT_LIST_HEAD(ptr) 是用来对已经定义的 struct list_head 类型的变量指针进行初始化
- __list_add(struct list_head *new, struct list_head *prev, struct list_head *next) 函数是将 struct list_head 类型的双向链表指针 new 插入到 prev 和 next 之间
- list_add(struct list_head *new, struct list_head *head) 函数是将 struct list_head 类型的双向链表指针 new 插入到 head 和 head->next 之间。如果多次使用该函数将多个双向链表插入到头指针之后，从头指针去访问插入的链表会出现一种类似于栈的现象，先进的后被访问，后进的先被访问。
- list_add_tail(struct list_head *new, struct list_head *head) 函数是将 struct list_head 类型的双向链表指针 new 插入到 head->prev 和 head之间。如果多次使用该函数将多个双向链表插入到头指针之后，从头指针去访问插入的链表会出现一种类似于队列的现象，先进的先被访问，后进的后被访问
- __list_del(struct list_head *prev, struct list_head *next) 函数是将 struct list_head 类型的双向链表指针 prev 和 next 连起来，原来的两者之间的那个双向链表的指向没变
- list_del(struct list_head *entry) 函数是将 struct list_head 类型的双向链表删除，首先是调用 __list_del(struct list_head *prev, struct list_head *next) 函数将 prev 和 next 两个双向链表连接起来，然后将要删除的 entry 双向链表结构体内的 prev 和 next 指针置为 NULL
- list_del_init(struct list_head *entry) 函数与 list_del(struct list_head *entry) 的区别在于调用 __list_del(struct list_head *prev, struct list_head *next) 函数将entry的前后两个链表连接起来之后，list_del_init(struct list_head *entry) 函数会将 entry 指针初始化， list_del(struct list_head *entry) 则会将 entry 指针置空
- list_move(struct list_head *list, struct list_head *head) 函数是将struct list_head类型的双向链表 list 的前后两个链表连接起来，然后将 list 双向链表插入到 head 头指针的双向链表之后（head 和 head->next 之间）
- list_move_tail(struct list_head *list, struct list_head *head) 函数是将struct list_head类型的双向链表 list 的前后两个链表连接起来，然后将 list 双向链表插入到 head 头指针的双向链表之前（head->prev 和 head 之间）
- list_empty(struct list_head *head) 函数是判断以 head 为头指针的双向链表是否为空（即只有初始化了的头指针）
- __list_splice(struct list_head *list, struct list_head *head) 函数是将以 list 和 head 为头指针的双向链表合并，合并后的双向链表的头指针是 head，原来的头指针 list 的指向没变。
- list_splice(struct list_head *list, struct list_head *head) 函数是在判断 list 头指针的双向链表不为空的情况下调用 __list_splice(struct list_head *list, struct list_head *head) 将以 list 和 head 为头指针的双向链表合并，合并后的双向链表的头指针还是 head
- list_splice_init(struct list_head *list, struct list_head *head) 函数是为了解决 list_splice(struct list_head *list, struct list_head *head) 函数中原头指针 list 的指向没变的问题，将 list 头指针再次初始化
17.
list_for_each_entry(pos, head, member) 宏和 list_for_each_entry_safe(pos, n, head, member) 宏跟其他 lis_for_* 系列的宏的区别就在于 pos 或者 n 变量是带有 struct list_head 类型的结构体指针，其他 list_for_* 系列的宏中 pos 则是 struct list_head 类型的一个变量指针