源码分析

#define BIT_WORD(nr)            ((nr) / BITS_PER_LONG)

BIT_WORD 宏用于计算 nr 个 bit 占用多少个字，这里字的长度是 BITS_PER_LONG，且计算出来的字长度比实际少一个，这也是一种向下对齐。参数 nr 代表 bit 的总数。函数将 nr 的值除以 BITS_PER_LONG 以此向下计算出 nr 个 bit 占了多少个字。

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)
{
	printk("BIT_WORD(0):   %#x\n", BIT_WORD(0));
	printk("BIT_WORD(15):  %#x\n", BIT_WORD(15));
	printk("BIT_WORD(31):  %#x\n", BIT_WORD(31));
	printk("BIT_WORD(32):  %#x\n", BIT_WORD(32));
	printk("BIT_WORD(33):  %#x\n", BIT_WORD(33));
	printk("BIT_WORD(63):  %#x\n", BIT_WORD(63));
	printk("BIT_WORD(64):  %#x\n", BIT_WORD(64));
	printk("BIT_WORD(65):  %#x\n", BIT_WORD(65));
	printk("BIT_WORD(90):  %#x\n", BIT_WORD(90));

	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 "BIT_WORD"
+
+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
            [*]BIT_WORD()

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
BIT_WORD(0):   0x0
BIT_WORD(15):  0x0
BIT_WORD(31):  0x0
BIT_WORD(32):  0x1
BIT_WORD(33):  0x1
BIT_WORD(63):  0x1
BIT_WORD(64):  0x2
BIT_WORD(65):  0x2
BIT_WORD(90):  0x2
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

BIT_WORD() 宏用于计算 nr 个 bit 占用的字数。

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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