Email: BuddyZhang1 buddy.zhang@aliyun.com
目录
源码分析
int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp)
{
u32 id = idr->idr_next;
int err, max = end > 0 ? end - 1 : INT_MAX;
if ((int)id < start)
id = start;
err = idr_alloc_u32(idr, ptr, &id, max, gfp);
if ((err == -ENOSPC) && (id > start)) {
id = start;
err = idr_alloc_u32(idr, ptr, &id, max, gfp);
}
if (err)
return err;
idr->idr_next = id + 1;
return id;
}
EXPORT_SYMBOL(idr_alloc_cyclic);idr_alloc_cyclic() 函数用于周期性的分配 ID，并将 ID 与 指针进行绑定。参数 idr 指向 idr 的根节点；参数 ptr 指向与 ID 进行绑定的指针；start 参数限定了 ID 的起始 值；参数 end 限定了 ID 的终止值；参数 gfp 指向了分配时需要的标识。函数从 idr->idr_next 成员中获得 id 值，然后判断 id 是否比 start 小，如果小则将 id 设置为 start。接着调用 idr_alloc_u32() 函数从 IDR 总分配一个 ID，并将 ptr 与 ID 进行绑定。如果 ID 分配失败，那么将 id 设置为 start 从新分配 ID；如果成功 分配，则将 idr->idr_next 指向 id+1.
实践
驱动源码
/*
* IDR.
*
* (C) 2019.06.04 <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.
*/
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/mm.h>
/* header of radix-tree */
#include <linux/idr.h>
/* private node */
struct node {
const char *name;
};
/* Root of IDR */
static DEFINE_IDR(BiscuitOS_idr);
/* node set */
static struct node node0 = { .name = "IDA" };
static struct node node1 = { .name = "IDB" };
static struct node node2 = { .name = "IDC" };
static struct node node3 = { .name = "IDD" };
static struct node node4 = { .name = "IDE" };
/* ID array */
#define IDR_ARRAY_SIZE 5
static int idr_array[IDR_ARRAY_SIZE];
static __init int idr_demo_init(void)
{
struct node *np;
int id;
/* proload for idr_alloc */
idr_preload(GFP_KERNEL);
/* Allocate a id from IDR */
idr_array[0] = idr_alloc_cyclic(&BiscuitOS_idr, &node0, 1,
INT_MAX, GFP_ATOMIC);
idr_array[1] = idr_alloc_cyclic(&BiscuitOS_idr, &node1, 1,
INT_MAX, GFP_ATOMIC);
idr_array[2] = idr_alloc_cyclic(&BiscuitOS_idr, &node2, 1,
INT_MAX, GFP_ATOMIC);
idr_array[3] = idr_alloc_cyclic(&BiscuitOS_idr, &node3, 1,
INT_MAX, GFP_ATOMIC);
idr_array[4] = idr_alloc_cyclic(&BiscuitOS_idr, &node4, 1,
INT_MAX, GFP_ATOMIC);
/* Interate over all slots */
idr_for_each_entry(&BiscuitOS_idr, np, id)
printk("%s's ID %d\n", np->name, id);
/* end preload section started with idr_preload() */
idr_preload_end();
return 0;
}
device_initcall(idr_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 atomic.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_IDR
+ bool "IDR"
+
+if BISCUITOS_IDR
+
+config DEBUG_BISCUITOS_IDR
+ bool "idr_alloc_cyclic"
+
+endif # BISCUITOS_IDR
+
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_IDR) += idr.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--->
[*]IDR
[*]idr_alloc_cyclic()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
IDA's ID 0
IDB's ID 1
IDC's ID 2
IDD's ID 3
IDE's ID 4
aaci-pl041 10004000.aaci: ARM AC'97 Interface PL041 rev0 at 0x10004000, irq 24
aaci-pl041 10004000.aaci: FIFO 512 entries
oprofile: using arm/armv7-ca9驱动分析
分配一个 ID，并将 ID 与一个指针相互绑定。
附录
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