我正在尝试执行我创建的linux模块的一个函数。但我没有成功。这是project
我创建了一个小函数来将int转换为str float：

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/string.h>

#include "service.h"
#include "fp_printk.h"

#define OURMODNAME "fp_printk"

MODULE_AUTHOR("Guilherme Giacomo Simoes <trintaeoitogc@gmail.com>");
MODULE_DESCRIPTION("This lib will show float-point in printk()");
MODULE_LICENSE("MIT");
MODULE_VERSION("0.4.1");

void fp_printk(int number, int decimal_places, char* destination)
{
    static char buffer[32] = { 0 };
    int buf_index = 30;
    int count_decimal_place = 0;
    int point_include = 0;

    for (; number && buf_index; --buf_index, number /= 10) {
        count_decimal_place++;
        if (!point_include && count_decimal_place > decimal_places) {
            buffer[buf_index] = '.';
            buf_index--;
            point_include = 1;
        }

        buffer[buf_index] = "0123456789"[number % 10];
    }

    strcpy(destination, &buffer[buf_index + 1]);
}

static int __init fp_printk_init(void)
{
    printk(KERN_INFO "%s: initial execute module", OURMODNAME);
    return 0;
}

static void __exit fp_printk_exit(void)
{
    printk(KERN_INFO "%s: module end", OURMODNAME);
}

module_init(fp_printk_init);
module_exit(fp_printk_exit);

EXPORT_SYMBOL(fp_printk);

转换后，将str复制到目标参数。
在我的测试模块中，我调用：

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <asm/fpu/api.h>
#include <linux/slab.h>

#include "../fp_printk.h"

MODULE_AUTHOR("Guilherme Giacomo Simoes <trintaeoitogc@gmail.com>");
MODULE_DESCRIPTION("LKP book:ch5/fp_in_lkm: no performing FP \
(floating point) arithmetic in kernel mode");
MODULE_LICENSE("Dual MIT/GPL");
MODULE_VERSION("0.1");

static int __init fp_in_lkm_init(void)
{
    const int number = 1234;
    const int decimal_places = 2;

    char *r = (char*) kmalloc(sizeof("12.34"), GFP_KERNEL);

    printk(KERN_INFO "antes de executar\n");
    extern void fp_printk(number, decimal_places, r);
    printk(KERN_INFO "teste apos a conversao");
    printk(KERN_INFO "%s",r);
    printk(KERN_INFO "teste apos o printk");

    return 0;
}

static void __exit fp_in_lkm_exit(void)
{
    printk(KERN_INFO "removed\n");
}

module_init(fp_in_lkm_init);
module_exit(fp_in_lkm_exit);

但是当我运行sudo dmesg查看printks时，我只查看：

[1210228.128703] test_fp_printk: antes de executar
[1210228.128712] test_fp_printk: teste apos a conversao

它不打印字符串
如果我在module_init中调用fp_printk（），它就会工作。

static int __init fp_printk_init(void)
{
    printk(KERN_INFO "%s: initial execute module", OURMODNAME);
    char *dest = kmalloc(sizeof("12.34"), GFP_KERNEL);
    fp_printk(1243, 2, dest); 
    printk(KERN_INFO, "%s", dest);
    return 0;
}