[Github: __atomic_test_and_clear_bit](https://github.com/BiscuitOS/HardStack/tree/master/Algorithem/bitmap/API/ __atomic_test_and_clear_bit)
Email: BuddyZhang1 buddy.zhang@aliyun.com
目录
源码分析
static inline int
____atomic_test_and_clear_bit( unsigned int bit, volatile unsigned long * p)
{
unsigned long flags;
unsigned int res;
unsigned long mask = BIT_MASK( bit) ;
p += BIT_WORD( bit) ;
raw_local_irq_save( flags) ;
res = * p;
* p = res & ~mask;
raw_local_irq_restore( flags) ;
return ( res & mask) != 0;
}
____atomic_test_and_clear_bit() 函数用于原子操作将 bitmap 指定的 bit 清零,
并返回清零前的值。参数 bit 对应需要清零的位置;参数 p 指向 bitmap 所在内存的
位置。函数首先调用 BIT_MASK() 函数生成只有 bit 置位的掩码,然后计算 bit 在
bitmap 的内存位置。接着调用 raw_local_irq_save() 函数上锁,上锁之后,读取
bitmap 的原始值到 ret 里,然后将 res 的值与 mask 的反码相与,以此清除 bit
对应的位,再将结果存储到 p 对应的内存,最后调用 raw_local_irq_restore()
函数解锁。最后返回 bit 的原始值。
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 = 0xff ;
int ret ;
/* Clear bit and return legacy value */
ret = ____atomic_test_and_clear_bit ( 1 , & bit );
printk ( "%#lx bit 1 legacy value 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 "____atomic_test_and_clear_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
[ * ] ____atomic_test_and_clear_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
0xfd bit 1 legacy value is: 1
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
清零 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
赞赏一下吧 🙂