註釋:文章最後是完成的代碼
設備環境說明:
1 ubuntu 18.04
2 arm-linux-gnueabihf-gcc (直接在新力得或者sudo apt install gcc-arm-linux-gnueabihf 指令下載即可)
3 使用周立功 M6Y2C 開發板進行測試
4 芯片是 Cortex-A7 Nxp imx6ul
說明
本次主要測試原子鎖
原子鎖的主要應用場景是在於整形和位操作
在實際多線程運行過程中,可能導致多條指令會被內核分成多次分開執行這就有可能產生問題,原子鎖就是將它們捆綁一體強制要求內核順序一次性將其執行完畢
線程A 線程B
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B
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實際我們的目標
線程A 線程B
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B
C
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C
使用步驟
- 定義
32bit:atmoic_t a;
64bit:atmoic64_t a; - 常見操作
函數 | 描述 |
---|---|
ATOMIC_INIT(int i) | //定義原子變量初始化 |
int atomic_read(atomic_t *v) | 讀取 v 值 |
void atomic_set(atomic_t *v, int i) | 寫入 i 值 |
void atomic_add(int i, atomic_t *v) | 加上 i 值 |
void atomic_sub(int i, atomic_t *v) | 減去 i 值 |
void atomic_inc(atomic_t *v) | 加 1,自增 |
void atomic_dec(atomic_t *v) | 減 1,自減 |
int atomic_dec_return(atomic_t *v) | 自減 1, 並返回 v |
int atomic_inc_return(atomic_t *v) | 自增 1, 並返回 v |
int atomic_sub_and_test(int i, atomic_t *v) | 減去 i,結果爲 0 返回真,其餘返回假 |
int atomic_dec_and_test(atomic_t *v) | 自減 1,結果爲 0 返回真,其餘返回假 |
int atomic_inc_and_test(atomic_t *v) | 自增 1,結果爲 0 返回真,其餘返回假 |
int atomic_add_negative(int i, atomic_t *v) | 加上 i,結果爲負返回真,其餘返回假 |
- e.g:
atomic_t v = ATMOIC_INIT(0);
atomic_set(10);
atomic_read(&v);
atomic_inc(&v); // 自增 1,11
- 位操作
原子位操作,是直接對內存操作
函數 | 描述 |
---|---|
void set_bit(int nr, void *p) | 將 p 地址的第 nr 位 置 1 |
void clear_bit(int nr, void *p) | 清 0 |
void change_bit(int nr, void *p) | 反轉 |
void test_bit(int nr, void *p) | 獲取值 |
void test_and_set_bit(int nr, void* p) | 讀取原值,並設置爲 1 |
void test_and_clear_bit(int nr, void* p) | 讀取原值,並清 0 |
void test_and_change_bit(int nr, void* p) | 讀取原值,並反轉 |
函數解析
- 在初始化函數中,初始化
atomic_set(&gpioled.lock, 1);
- 在 open 函數中,判斷鎖的狀態
// 檢查是否被使用 這個函數本質就是先自減 1 然後判斷是否爲0
if (!atomic_long_dec_and_test(&gpioled.lock)) {
//這邊需要自增 1, 以確保負值變 0
atomic_inc(&gpioled.lock);
return -EBUSY; //返回忙的狀態
}
- 在 release 函數中,釋放鎖的狀態
struct gpioled_dev *dev = filp->private_data;
atomic_inc(&dev->lock);
return 0;
測試方法
./atomiclock /dev/gpioled 1 &
//& 移到後臺執行
./atomiclock /dev/gpioled 0
以上就是原子鎖的實驗
源碼
atomiclock.c 驅動程序
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/ide.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/gpio.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_gpio.h>
#include <asm/mach/map.h>
#include <asm/uaccess.h>
#include <asm/io.h>
#define GPIOLED_CNT 1 //個數
#define GPIOLED_NAME "gpioled"
#define LEDOFF 0
#define LEDON 1
struct gpioled_dev {
dev_t devid; //設備號
struct cdev cdev; //cdev
struct class *class; //類
struct device *device; //設備
int major; //主設備號
int minor; //次設備號
struct device_node *nd; //設備節點
int led_gpio; //led gpio 編號
atomic_t lock; //原子鎖
};
struct gpioled_dev gpioled;
static int led_open(struct inode* inode, struct file* filp)
{
//檢查是否已被使用
if (!atomic_long_dec_and_test(&gpioled.lock)) {
atomic_inc(&gpioled.lock); //小於 0 就 +1, 使其原子變量等於 0
return -EBUSY; //LED 被使用返回忙
}
filp->private_data = &gpioled;
return 0;
}
static ssize_t led_read(struct file* filp, char __user *buf,
size_t cnt, loff_t* offt)
{
return 0;
}
static ssize_t led_write(struct file* filp, const char __user* buf,
size_t cnt, loff_t* offt)
{
int retvalue = 0;
unsigned char databuf[1];
unsigned char ledstat = 0;
struct gpioled_dev* dev = filp->private_data;
retvalue = copy_from_user(databuf, buf, cnt);
if (retvalue < 0) {
printk("kernel write failed \n");
return -EFAULT;
}
ledstat = databuf[0];
printk("gpio: %d Status: %d \n", dev->led_gpio, ledstat);
if (LEDON == ledstat) {
gpio_set_value(dev->led_gpio, 0); //打開LED
} else if (LEDOFF == ledstat) {
gpio_set_value(dev->led_gpio, 1);
}
return 0;
}
static int led_release(struct inode *inode, struct file *filp)
{
struct gpioled_dev *dev = filp->private_data;
//關閉驅動文件的時候釋放原子變量
atomic_inc(&dev->lock);
return 0;
}
static struct file_operations gpioled_fops = {
.owner = THIS_MODULE,
.open = led_open,
.read = led_read,
.write = led_write,
.release = led_release,
};
static int __init led_init(void)
{
int ret = 0;
//初始化原子變量
atomic_set(&gpioled.lock, 1);
gpioled.nd = of_find_node_by_path("/gpioled");
if (gpioled.nd == NULL) {
printk("gpioled node not find! \n");
return -EINVAL;
} else {
printk("gpioled node find! \n");
}
gpioled.led_gpio = of_get_named_gpio(gpioled.nd, "led-gpio", 0);
if (gpioled.led_gpio < 0) {
printk ("can't get led-gpio \n");
return -EINVAL;
}
printk("led-gpio num = %d \n", gpioled.led_gpio);
ret = gpio_direction_output(gpioled.led_gpio, 0);
if (ret < 0) {
printk("can't set gpio \n");
}
if (gpioled.major) {
gpioled.devid = MKDEV(gpioled.major, 0);
register_chrdev_region(gpioled.devid, GPIOLED_CNT, GPIOLED_NAME);
} else {
alloc_chrdev_region(&gpioled.devid, 0, GPIOLED_CNT, GPIOLED_NAME);
gpioled.major = MAJOR(gpioled.devid);
gpioled.minor = MINOR(gpioled.devid);
}
printk("gpioled major = %d, minor = %d \n", gpioled.major, gpioled.minor);
gpioled.cdev.owner = THIS_MODULE;
cdev_init(&gpioled.cdev, &gpioled_fops);
cdev_add(&gpioled.cdev, gpioled.devid, GPIOLED_CNT);
gpioled.class = class_create(THIS_MODULE, GPIOLED_NAME);
if (IS_ERR(gpioled.class)) {
return PTR_ERR(gpioled.class);
}
gpioled.device = device_create(gpioled.class, NULL, gpioled.devid,
NULL, GPIOLED_NAME);
if (IS_ERR(gpioled.device)) {
return PTR_ERR(gpioled.device);
}
return 0;
}
static void __exit led_exit(void)
{
cdev_del(&gpioled.cdev);
unregister_chrdev_region(gpioled.devid, GPIOLED_CNT);
device_destroy(gpioled.class, gpioled.devid);
class_destroy(gpioled.class);
}
module_init(led_init);
module_exit(led_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("zzz");
測試 APP
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#define LEDOFF 0
#define LEDON 1
int main(int argc, char* argv[])
{
int fd, retvalue;
char* filename;
unsigned char cnt = 0;
unsigned char databuf[1];
if (argc != 3) {
printf("Error Usage! \n");
return -1;
}
filename = argv[1];
fd = open(filename, O_RDWR);
if (fd < 0) {
printf("file %s open failed ! \n", argv[1]);
return -1;
}
databuf[0] = atoi(argv[2]);
retvalue = write(fd, databuf, sizeof(databuf));
if (retvalue < 0) {
printf("LED Control Failed ! \n");
return -1;
}
//模擬佔用 25s LED
while(1) {
sleep(5);
cnt++;
printf("App running times: %d \n", cnt);
if (cnt >= 5) break;
}
printf("App running finished \n");
retvalue = close(fd);
if (retvalue < 0) {
printf("file %s close failed !\n", argv[1]);
return -1;
}
return 0;
}
Makefile
KERNELDIR := /home/x/workspace/01_linux_kernel/test/imx_4.1.15_2.0.0_ga_rc3/
CURRENT_PATH := $(shell pwd)
obj-m := atomiclock.o
build: kernel_modules
kernel_modules:
$(MAKE) ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- EXTRA_CFLAGS=-fno-pic -C $(KERNELDIR) M=`pwd` modules
clean:
$(MAKE) ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- -C $(KERNELDIR) M=`pwd` clean
App 編譯指令
arm-linux-gnueabihf-gcc atomiclock_app.c -o atomiclock
設備樹配置
/ {
gpioled {
compatible = "atkalpha-gpioled";
#address-cells = <1>;
#size-cells = <1>;
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_led>;
led-gpio = <&gpio4 14 GPIO_ACTIVE_LOW>;
status = "okay";
};
};
&iomuxc{
pinctrl_led: ledgrp {
fsl,pins = <
MX6UL_PAD_NAND_CE1_B__GPIO4_IO14 0x40017059
>;
};
};