Email: BuddyZhang1 buddy.zhang@aliyun.com
目录
源码分析
/**
* list_cut_position - cut a list into two
* @list: a new list to add all removed entries
* @head: a list with entries
* @entry: an entry within head, could be the head itself
* and if so we won't cut the list
*
* This helper moves the initial part of @head, up to and
* including @entry, from @head to @list. You should
* pass on @entry an element you know is on @head. @list
* should be an empty list or a list you do not care about
* losing its data.
*
*/
static inline void list_cut_position(struct list_head *list,
struct list_head *head, struct list_head *entry)
{
if (list_empty(head))
return;
if (list_is_singular(head) &&
(head->next != entry && head != entry))
return;
if (entry == head)
INIT_LIST_HEAD(list);
else
__list_cut_position(list, head, entry);
}list_cut_position() 函数用于将一个链表切成两个链表。参数 list 指向一个新的链表， 参数 head 指向被拆开的链表 (原始链表)，entry 参数指向拆开的位置。函数首先调用 list_empty() 函数确定 head 链表是不是空链表，如果是则直接返回；如果不是空链表， 则调用 list_is_singular() 函数确定 head 链表是不是单一节点的链表，如果是则判断 head 链表的 next 不指向 entry 参数，并且 head 不是 entry，那么直接返回；反之 不是，则判断 entry 与 head 的关系，如果 entry 就是 head，那么代表新链表是空链表， 那么直接调用 INIT_LIST_HEAD() 函数初始化 list 链表；反之调用 __list_cut_position() 将 head 链表拆成两段，第一个节点到 entry 节点的链表使用 list 指定，entry 到最后一个 节点通过 head 指向。
list_is_singular
INIT_LIST_HEAD
__list_cut_position
实践
驱动源码
/*
* bindirect-list
*
* (C) 20179.04.25 <buddy.zhang@aliyun.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
/*
* bidirect-list
*
* +-----------+<--o +-----------+<--o +-----------+<--o +-----------+
* | | | | | | | | | | |
* | prev | o----| prev | o----| prev | o----| prev |
* | list_head | | list_head | | list_head | | list_head |
* | next |---o | next |---o | next |---o | next |
* | | | | | | | | | | |
* +-----------+ o--->+-----------+ o--->+-----------+ o--->+-----------+
*
*/
#include <linux/kernel.h>
#include <linux/init.h>
/* header of list */
#include <linux/list.h>
/* private structure */
struct node {
const char *name;
struct list_head list;
};
/* Initialize a group node structure */
static struct node node0 = { .name = "BiscuitOS_node0", };
static struct node node1 = { .name = "BiscuitOS_node1", };
static struct node node2 = { .name = "BiscuitOS_node2", };
static struct node node3 = { .name = "BiscuitOS_node3", };
static struct node node4 = { .name = "BiscuitOS_node4", };
static struct node node5 = { .name = "BiscuitOS_node5", };
static struct node node6 = { .name = "BiscuitOS_node6", };
/* Declaration and implement a bindirect-list */
LIST_HEAD(BiscuitOS_list);
LIST_HEAD(BiscuitOS_blist);
static __init int bindirect_demo_init(void)
{
struct node *np;
/* add a new entry on special entry */
list_add_tail(&node0.list, &BiscuitOS_list);
list_add_tail(&node1.list, &BiscuitOS_list);
list_add_tail(&node2.list, &BiscuitOS_list);
list_add_tail(&node3.list, &BiscuitOS_list);
list_add_tail(&node4.list, &BiscuitOS_list);
list_add_tail(&node5.list, &BiscuitOS_list);
list_add_tail(&node6.list, &BiscuitOS_list);
/* Cut BiscuitOS_list and cat into BiscuitOS_blist */
list_cut_position(&BiscuitOS_blist, &BiscuitOS_list, &node3.list);
printk("BiscuitOS_list:\n");
/* Traverser all node on bindirect-list */
list_for_each_entry(np, &BiscuitOS_list, list)
printk("%s\n", np->name);
printk("BiscuitOS_blist:\n");
/* Traverser all node on bindirect-list */
list_for_each_entry(np, &BiscuitOS_blist, list)
printk("%s\n", np->name);
return 0;
}
device_initcall(bindirect_demo_init);驱动安装
驱动的安装很简单，首先将驱动放到 drivers/BiscuitOS/ 目录下，命名为 list.c， 然后修改 Kconfig 文件，添加内容参考如下：
diff --git a/drivers/BiscuitOS/Kconfig b/drivers/BiscuitOS/Kconfig
index 4edc5a5..1a9abee 100644
--- a/drivers/BiscuitOS/Kconfig
+++ b/drivers/BiscuitOS/Kconfig
@@ -6,4 +6,14 @@ if BISCUITOS_DRV
config BISCUITOS_MISC
bool "BiscuitOS misc driver"
+config BISCUITOS_LIST
+ bool "Bindirect-list"
+
+if BISCUITOS_LIST
+
+config DEBUG_BISCUITOS_LIST
+ bool "list_cut_position"
+
+endif # BISCUITOS_LIST
+
endif # BISCUITOS_DRV接着修改 Makefile，请参考如下修改：
diff --git a/drivers/BiscuitOS/Makefile b/drivers/BiscuitOS/Makefile
index 82004c9..9909149 100644
--- a/drivers/BiscuitOS/Makefile
+++ b/drivers/BiscuitOS/Makefile
@@ -1 +1,2 @@
obj-$(CONFIG_BISCUITOS_MISC) += BiscuitOS_drv.o
+obj-$(CONFIG_BISCUITOS_LIST) += list.o
--驱动配置
驱动配置请参考下面文章中关于驱动配置一节。在配置中，勾选如下选项，如下：
Device Driver--->
[*]BiscuitOS Driver--->
[*]Bindirect-list
[*]list_cut_position()具体过程请参考：
驱动编译
驱动编译也请参考下面文章关于驱动编译一节：
驱动运行
驱动的运行，请参考下面文章中关于驱动运行一节：
启动内核，并打印如下信息：
usbcore: registered new interface driver usbhid
usbhid: USB HID core driver
BiscuitOS_list:
BiscuitOS_node4
BiscuitOS_node5
BiscuitOS_node6
BiscuitOS_blist:
BiscuitOS_node0
BiscuitOS_node1
BiscuitOS_node2
BiscuitOS_node3
aaci-pl041 10004000.aaci: ARM AC'97 Interface PL041 rev0 at 0x10004000, irq 24
aaci-pl041 10004000.aaci: FIFO 512 entries驱动分析
在需要将一个链表拆分成两个链表的时候，可以使用 list_cut_position() 函数完成功能。
附录
赞赏一下吧 🙂
