//mmap.c

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <string.h>

int main(int argc, char const *argv[])
{
    int fd = open("mem.txt", O_RDWR | O_CREAT | O_TRUNC, 0644);    //创建并截断文件
    //int fd = open("mem.txt", O_WRONLY | O_CREAT | O_TRUNC, 0644);   //Permission denied

    ftruncate(fd, 20);       //open的时候，可以创建一个文件来创建映射区，但前提是文件大小不能为0
    //创建映射区
    char *mem = mmap(NULL, 20, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    //offset必须是4k的整数倍
    //char *mem = mmap(NULL, 5, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 4096);
    //char *mem = mmap(NULL, 5, PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, 0);
    if (mem == MAP_FAILED)
    {
        perror("mmap err!");
        return -1;
    }
    strcpy(mem, "hello world");
    
    //close(fd);        /如果文件描述符先关闭，对mmap映射没有影响，因为映射通道已经通了
    //mem++;            //不能改变地址，否则无法释放
    //释放
    int ret = munmap(mem, 20);
    if (ret < 0)
    {
        perror("munmap error!");
    }
    close(fd);
    return 0;
}

//mmap_fork.c

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <fcntl.h>

int main(int argc, char const *argv[])
{
    //先创建映射区
    int fd = open("mem.txt", O_RDWR);
    int *mem = mmap(NULL, 4, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    //int *mem = mmap(NULL, 4, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
    if (mem == MAP_FAILED)
    {
        perror("mmap error!");
        return -1;
    }

    //fork子进程
    pid_t pid = fork();
    //父进程和子进程交替修改数据
    if (pid < 0)
    {
        perror("fork error!");
        return -1;
    }
    else if (pid == 0)
    {
        *mem = 100;
        printf("child, *mem = %d\n", *mem);
        sleep(3);
        printf("child, *mem = %d\n", *mem);
    }
    else if (pid > 0)
    {
        sleep(1);
        printf("parent, *mem = %d\n", *mem);
        *mem = 1001;
        printf("parent, *mem = %d\n", *mem);
        wait(NULL);
    }

    int ret = munmap(mem, 4);
    if (ret < 0)
    {
        perror("munmap failed!");
        return -1;
    }
    close(fd);
    return 0;
}

//mmpa_anon.c

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <fcntl.h>

int main(int argc, char const *argv[])
{
    int *mem = mmap(NULL, 4, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANON, -1, 0);
    if (mem == MAP_FAILED)
    {
        perror("mmap error!");
        return -1;
    }

        //fork子进程
    pid_t pid = fork();
    //父进程和子进程交替修改数据
    if (pid < 0)
    {
        perror("fork error!");
        return -1;
    }
    else if (pid == 0)
    {
        *mem = 100;
        printf("child, *mem = %d\n", *mem);
        sleep(3);
        printf("child, *mem = %d\n", *mem);
    }
    else if (pid > 0)
    {
        sleep(1);
        printf("parent, *mem = %d\n", *mem);
        *mem = 1001;
        printf("parent, *mem = %d\n", *mem);
        wait(NULL);
    }

    int ret = munmap(mem, 4);
    if (ret < 0)
    {
        perror("munmap failed!");
        return -1;
    }
    return 0;
}

//mmap_read.c

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <fcntl.h>

typedef struct Student
{
    int sid;
    char sname[20];
}Student;

int main(int argc, char const *argv[])
{
    if (argc != 2)
    {
        printf("./a.out filename\n");
        return -1;
    }

    //1.open file
    int fd = open(argv[1], O_RDWR, 0666);
    int length = sizeof(Student);

    //2.mmap
    Student *stu = mmap(NULL, length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if (stu == MAP_FAILED)
    {
        perror("map error!");
        return -1;
    }

    //3.修改内存数据, read
    while (1)
    {//每隔一秒读一次映射区的内容
        printf("sid = %d, sname = %s\n", stu->sid, stu->sname);
        sleep(1);
    }
    //4.释放映射区和关闭描述符
    int ret = munmap(stu, length);
    if (ret < 0)
    {
        perror("munmap failed!");
        return -1;
    }
    close(fd);
    return 0;
}

//mmap_write.c

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <fcntl.h>

typedef struct Student
{
    int sid;
    char sname[20];
}Student;

int main(int argc, char const *argv[])
{
    if (argc != 2)
    {
        printf("./a.out filename\n");
        return -1;
    }

    //1.open file
    int fd = open(argv[1], O_CREAT | O_RDWR | O_TRUNC, 0666);
    int length = sizeof(Student);
    ftruncate(fd, length);

    //2.mmap
    Student *stu = mmap(NULL, length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if (stu == MAP_FAILED)
    {
        perror("map error!");
        return -1;
    }

    //3.修改内存数据, write
    int num = 1;
    while (1)
    {//每隔一秒修改一次映射区的内容
        stu->sid = num;
        sprintf(stu->sname, "LiHua-%03d", num++);
        sleep(1);
    }
    //4.释放映射区和关闭描述符
    int ret = munmap(stu, length);
    if (ret < 0)
    {
        perror("munmap failed!");
        return -1;
    }
    close(fd);
    return 0;
}