源码分析

/**
 * ida_destroy() - Free all IDs.
 * @ida: IDA handle.
 *
 * Calling this function frees all IDs and releases all resources used
 * by an IDA.  When this call returns, the IDA is empty and can be reused
 * or freed.  If the IDA is already empty, there is no need to call this
 * function.
 *
 * Context: Any context.
 */
void ida_destroy(struct ida *ida)
{
        unsigned long flags;
        struct radix_tree_iter iter;
        void __rcu **slot;

        xa_lock_irqsave(&ida->ida_rt, flags);
        radix_tree_for_each_slot(slot, &ida->ida_rt, &iter, 0) {
                struct ida_bitmap *bitmap = rcu_dereference_raw(*slot);
                if (!radix_tree_exception(bitmap))
                        kfree(bitmap);
                radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
        }
        xa_unlock_irqrestore(&ida->ida_rt, flags);
}
EXPORT_SYMBOL(ida_destroy);

ida_destroy() 函数用于释放所有的 ID。参数 ida 指向 IDA。函数调用 xa_lock_irqsave() 函数加锁，然后调用 radix_tree_for_each_slot() 遍历 IDA radix-tree 树中的所有 slot，然后获得 slot 指向的 bitmap，如果 bitmap 不是 exceptional 节点，那么直接调用 kfree 进行释放。接着调用 radix_tree_iter_delete() 将对应的 slot 从 radix-tree 中抹除。遍历完毕之后，调用 xa_unlock_irqrestore() 解锁。

radix_tree_for_each_slot

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

/*
 * IDA.
 *
 * (C) 2019.06.04 <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>
#include <linux/mm.h>

/* header of IDA/IDR */
#include <linux/idr.h>
#include <linux/radix-tree.h>

/* Root of IDA */
static DEFINE_IDA(BiscuitOS_ida);

static __init int ida_demo_init(void)
{
	int id;

	/* Allocate an unused ID */
	id = ida_alloc_range(&BiscuitOS_ida, 0x10, INT_MAX,  GFP_KERNEL);
	printk("IDA-ID: %#x\n", id);

	/* Release an ID */
	ida_free(&BiscuitOS_ida, id);

	/* Free all IDs */
	ida_destroy(&BiscuitOS_ida);

	return 0;
}
device_initcall(ida_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 ida.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_IDA
+       bool "IDA"
+
+if BISCUITOS_IDA
+
+config DEBUG_BISCUITOS_IDA
+       bool "ida_destroy"
+
+endif # BISCUITOS_IDA
+
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_IDA)     += ida.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--->
        [*]IDA
            [*]ida_destroy()

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
IDA-ID: 0x10
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

移除 IDA 上所有的 ID。

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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MMU