Github: list_for_each_entry_safe_reverse
Email: BuddyZhang1 buddy.zhang@aliyun.com
目录
源码分析
/**
* list_for_each_entry_safe_reverse - iterate backwards over list safe against removal
* @pos: the type * to use as a loop cursor.
* @n: another type * to use as temporary storage
* @head: the head for your list.
* @member: the name of the list_head within the struct.
*
* Iterate backwards over list of given type, safe against removal
* of list entry.
*/
#define list_for_each_entry_safe_reverse(pos, n, head, member) \
for (pos = list_last_entry(head, typeof(*pos), member), \
n = list_prev_entry(pos, member); \
&pos->member != (head); \
pos = n, n = list_prev_entry(n, member))list_for_each_entry_safe_reverse() 用于安全倒叙遍历所有的入口。当出现每次遍历一个 入口之后需要将节点从双链表中移除，此时使用该函数不会引起内核 panic。参数 pos 指向当前遍历 到的入口； n 指向下一个遍历到的入口； head 指向双链表的表头；member 指明双链表在入口 结构中的名字。函数使用了一个 for 循环，首先调用 list_last_entry() 函数获得最后一个入口, 和使用 list_prev_entry() 获得倒数第二个入口，每次遍历过程中，使用 list_prev_entry() 函数获得前一个入口，通过这样的方法倒叙遍历所有的入口。
list_last_entry
list_prev_entry
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;
struct node *n;
/* 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);
printk("BiscuitOS_list:\n");
/* Traverser all node on bindirect-list */
list_for_each_entry(np, &BiscuitOS_list, list)
printk("%s\n", np->name);
printk("Coninue:\n");
/* iterate over list from current point safe against removal. */
list_for_each_entry_safe_reverse(np, n, &BiscuitOS_list, list) {
printk("%s\n", np->name);
list_del(&np->list);
}
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_for_each_entry_safe_reverse"
+
+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_for_each_entry_safe_reverse()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_node0
BiscuitOS_node1
BiscuitOS_node2
BiscuitOS_node3
BiscuitOS_node4
BiscuitOS_node5
BiscuitOS_node6
Coninue:
BiscuitOS_node6
BiscuitOS_node5
BiscuitOS_node4
BiscuitOS_node3
BiscuitOS_node2
BiscuitOS_node1
BiscuitOS_node0
input: AT Raw Set 2 keyboard as /devices/platform/smb@4000000/smb@4000000:motherboard/smb@4000000:motherboard:iofpga@7,00000000/10006000.kmi/serio0/input/input0驱动分析
当倒叙遍历过程中，涉及到删除当前节点操作，那么需要使用这个函数，否侧会引起内核 panic.
附录
赞赏一下吧 🙂
