Github: __test_and_set_bit
Email: BuddyZhang1 buddy.zhang@aliyun.com
目录
源码分析
/**
* __test_and_set_bit - Set a bit and return its old value
* @nr: Bit to set
* @addr: Address to count from
*
* This operation is non-atomic and can be reordered.
* If two examples of this operation race, one can appear to succeed
* but actually fail. You must protect multiple accesses with a lock.
* /
static inline int __test_and_set_bit( int nr, volatile unsigned long * addr)
{
unsigned long mask = BIT_MASK( nr) ;
unsigned long * p = (( unsigned long * ) addr) + BIT_WORD( nr) ;
unsigned long old = * p;
* p = old | mask;
return ( old & mask) != 0;
}
__test_and_set_bit() 函数的作用是读取 bit 中指定位的值,并将该位置位。参数
nr 指向需要修改的位置;参数 addr 指向 bit 所在的内存位置。函数首先调用
BIT_MASK() 函数获得 nr 置位的掩码,然后调用 BIT_WORD() 函数计算 nr 相对
addr 的 BITS_PER_LONG 偏移。然后读取 bit 的原始值存储在 old 里面。然后将
old 与 mask 相或,存储到 p 所指的内存,以此将 nr 对应的 bit 置位,最后
返回 nr 的原先值。
实践
驱动源码
/*
* Bitmap.
*
* (C) 2019.06.10 <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>
/* header of bitmap */
#include <linux/bitmap.h>
static __init int bitmap_demo_init ( void )
{
unsigned long bit = 0xf0 ;
int ret ;
/* Set a bit and return its old value */
ret = __test_and_set_bit ( 1 , & bit );
printk ( "%#lx before 1's bit is: %d \n " , bit , ret );
return 0 ;
}
device_initcall ( bitmap_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 bitmap.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_BITMAP
+ bool "bitmap"
+
+if BISCUITOS_BITMAP
+
+config DEBUG_BISCUITOS_BITMAP
+ bool "__test_and_set_bit"
+
+endif # BISCUITOS_BITMAP
+
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_BITMAP) += bitmap.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--->
[ * ] bitmap
[ * ] __test_and_set_bit()
具体过程请参考:
Linux 5.0 开发环境搭建 – 驱动配置
驱动编译
驱动编译也请参考下面文章关于驱动编译一节:
Linux 5.0 开发环境搭建 – 驱动编译
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:
Linux 5.0 开发环境搭建 – 驱动运行
启动内核,并打印如下信息:
usbcore: registered new interface driver usbhid
usbhid: USB HID core driver
0xf2 before 1's bit is: 0
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
test 与 set bit
附录
BiscuitOS Home
BiscuitOS Driver
BiscuitOS Kernel Build
Linux Kernel
Bootlin: Elixir Cross Referencer
搭建高效的 Linux 开发环境
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