/**
 * idr_replace() - replace pointer for given ID.
 * @idr: IDR handle.
 * @ptr: New pointer to associate with the ID.
 * @id: ID to change.
 *
 * Replace the pointer registered with an ID and return the old value.
 * This function can be called under the RCU read lock concurrently with
 * idr_alloc() and idr_remove() (as long as the ID being removed is not
 * the one being replaced!).
 *
 * Returns: the old value on success.  %-ENOENT indicates that @id was not
 * found.  %-EINVAL indicates that @ptr was not valid.
 */
void *idr_replace(struct idr *idr, void *ptr, unsigned long id)
{
        struct radix_tree_node *node;
        void __rcu **slot = NULL;
        void *entry;

        if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
                return ERR_PTR(-EINVAL);
        id -= idr->idr_base;

        entry = __radix_tree_lookup(&idr->idr_rt, id, &node, &slot);
        if (!slot || radix_tree_tag_get(&idr->idr_rt, id, IDR_FREE))
                return ERR_PTR(-ENOENT);

        __radix_tree_replace(&idr->idr_rt, node, slot, ptr, NULL);

        return entry;
}
EXPORT_SYMBOL(idr_replace);

/*
 * IDR.
 *
 * (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 radix-tree */
#include <linux/idr.h>

/* private node */
struct node {
	const char *name;
};

/* Root of IDR */
static DEFINE_IDR(BiscuitOS_idr);

/* node set */
static struct node node0 = { .name = "IDA" };
static struct node node1 = { .name = "IDB" };
static struct node node2 = { .name = "IDC" };
static struct node node3 = { .name = "IDD" };
static struct node node4 = { .name = "IDE" };

/* ID array */
#define IDR_ARRAY_SIZE	5
static int idr_array[IDR_ARRAY_SIZE];

static __init int idr_demo_init(void)
{
	struct node *np;
	int id;

	/* proload for idr_alloc */
	idr_preload(GFP_KERNEL);

	/* Allocate a id from IDR */
	idr_array[0] = idr_alloc_cyclic(&BiscuitOS_idr, &node0, 1,
							INT_MAX, GFP_ATOMIC);
	idr_array[1] = idr_alloc_cyclic(&BiscuitOS_idr, &node1, 1,
							INT_MAX, GFP_ATOMIC);
	idr_array[2] = idr_alloc_cyclic(&BiscuitOS_idr, &node2, 1,
							INT_MAX, GFP_ATOMIC);
	idr_array[3] = idr_alloc_cyclic(&BiscuitOS_idr, &node3, 1,
							INT_MAX, GFP_ATOMIC);

	/* Interate over all slots */
	idr_for_each_entry(&BiscuitOS_idr, np, id)
		printk("%s's ID %d\n", np->name, id);

	/* replace pointer for given ID */
	idr_replace(&BiscuitOS_idr, &node4, idr_array[1]);
	printk("Replace %d\n", idr_array[1]);

	/* Interate over all slots */
	idr_for_each_entry(&BiscuitOS_idr, np, id)
		printk("%s's ID %d\n", np->name, id);

	/* end preload section started with idr_preload() */
	idr_preload_end();

	return 0;
}
device_initcall(idr_demo_init);

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_IDR
+       bool "IDR"
+
+if BISCUITOS_IDR
+
+config DEBUG_BISCUITOS_IDR
+       bool "idr_replace"
+
+endif # BISCUITOS_IDR
+
endif # BISCUITOS_DRV

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_IDR)     += idr.o
--

Device Driver--->
    [*]BiscuitOS Driver--->
        [*]IDR
            [*]idr_replace()

usbcore: registered new interface driver usbhid
usbhid: USB HID core driver
IDA's ID 1
IDB's ID 2
IDC's ID 3
IDD's ID 4
Replace 2
IDA's ID 1
IDE's ID 2
IDC's ID 3
IDD's ID 4
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