源码分析

#if !defined(find_next_and_bit)
unsigned long find_next_and_bit(const unsigned long *addr1,
                const unsigned long *addr2, unsigned long size,
                unsigned long offset)
{
        return _find_next_bit(addr1, addr2, size, offset, 0UL);
}
EXPORT_SYMBOL(find_next_and_bit);
#endif

find_next_and_bit() 用于在指定的范围内找到第一个置位的 bit 位置。参数 addr1 指向被查找 bitmap；参数 addr2 作为查找范围内的掩码；size 参数表示查找的范围； offset 代表查找的起始位置。函数直接调用 _find_next_bit() 函数去查找一个置位的位置，注意 addr2 作为掩码，找到置位之后如果与掩码相与不符合要求也算找不到。

_find_next_bit

实践

驱动源码

驱动安装

驱动配置

驱动编译

驱动运行

驱动分析

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 bitmap1 = 0xfff00;
	unsigned long bitmap2 = 0x1ff;
	unsigned long pos;

	/* Find first set bit */
	pos = find_next_and_bit(&bitmap1, &bitmap2, 32, 0);
	printk("%#lx find first set bit through bit 0 to bit 32: %ld\n",
						bitmap1, 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 "find_next_and_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
            [*]find_next_and_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
0xfff00 find first set bit through bit 0 to bit 32: 8
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

查找置位 bit 的位置。

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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