Email: BuddyZhang1 buddy.zhang@aliyun.com
目录
源码分析
/**
* list_is_last - tests whether @list is the last entry in list @head
* @list: the entry to test
* @head: the head of the list
*/
static inline int list_is_last(const struct list_head *list,
const struct list_head *head)
{
return list->next == head;
}list_is_last() 函数用于检查节点是否位于链表的末尾。在双链表中，链表的最后一个节点 的 next 成员指向链表头，因此可以根据这个信息判断一个节点是否位于链表的末尾。
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);
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);
/* Test whether list is the last entry in head */
if (list_is_last(&node6.list, &BiscuitOS_list))
printk("%s is last node.\n", node6.name);
/* Test whether list is the last entry in head */
if (!list_is_last(&node5.list, &BiscuitOS_list))
printk("%s isn't last node.\n", node5.name);
printk("BiscuitOS_list:\n");
/* Traverser all node on bindirect-list */
list_for_each_entry(np, &BiscuitOS_list, 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_is_last"
+
+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_is_last()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_node6 is last node.
BiscuitOS_node5 isn't last node.
BiscuitOS_list:
BiscuitOS_node0
BiscuitOS_node1
BiscuitOS_node2
BiscuitOS_node3
BiscuitOS_node4
BiscuitOS_node5
BiscuitOS_node6
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
有时需要判断是否达到链表末尾，此时可以使用 list_is_last() 函数进行判断。
附录
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