Github: test_bit
Email: BuddyZhang1 buddy.zhang@aliyun.com
目录
源码分析
/**
* test_bit - Determine whether a bit is set
* @nr: bit number to test
* @addr: Address to start counting from
* /
static inline int test_bit( int nr, const volatile unsigned long * addr)
{
return 1UL & ( addr[BIT_WORD( nr)] >> ( nr & ( BITS_PER_LONG-1))) ;
}
test_bit() 用于检查 bitmap 中特定位置的 bit 是否已经置位,如果置位则返回 1,
反之返回 0. 参数 nr 指向 bit 的位置;参数 addr 指向 bitmap;函数首先调用
BIT_WORD() 函数计算 nr 位于第几个 long 中,然后将对于的 long 值读出后向右
移位 nr 之后,与 1 相与并直接返回结果。
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 bitmap = 0x90911016 ;
int pos = 4 ;
/* Test bit */
printk ( "Bitmap: %#lx test_bit(%d): %d \n " , bitmap , pos ,
test_bit ( pos , & bitmap ));
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_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_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
Bitmap: 0x90911016 test_bit( 4) : 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
检查置位。
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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