Email: BuddyZhang1 buddy.zhang@aliyun.com
目录
源码分析
/* same as for_each_set_bit_from() but use bit as value to start with */
#define for_each_set_bit_from(bit, addr, size) \
for ((bit) = find_next_bit((addr), (size), (bit)); \
(bit) < (size); \
(bit) = find_next_bit((addr), (size), (bit) + 1))for_each_set_bit_from() 函数用于从特定位置开始，遍历指定范围内的所有置位 bit。 参数 bit 指向开始遍历的位置；参数 addr 指向 bitmap；参数 size 指向查找的 范围。函数通过调用 find_next_bit() 获得 bit 指向位置处第一个置位的位置， 如果 bit 小于 size 继续遍历；每次遍历完毕之后，都是使用 find_next_bit() 继续查找下一个置位的位置。
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>
/* Declare bitmap */
DECLARE_BITMAP(bitmap, 32);
static __init int bitmap_demo_init(void)
{
unsigned long pos = 2;
bitmap_set(bitmap, 4, 8);
for_each_set_bit_from(pos, bitmap, 24)
printk("POS: %ld\n", pos);
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 "for_each_set_bit_from"
+
+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
[*]for_each_set_bit_from()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
POS: 4
POS: 5
POS: 6
POS: 7
POS: 8
POS: 9
POS: 10
POS: 11
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
遍历操作
附录
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