9、RK3399J 文件IO介绍

1、查看mount挂载情况

```go
cat  /proc/mounts

2、挂载虚拟文件系统

mount -t sysfs none /mnt

3、 文件从哪里来

4、内核的 sys_open、sys_read 会做什么？

5、app调用系统接口图

6、字符设备节点介绍

7、文件拷贝实例

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

/*
 * ./copy 1.txt 2.txt
 * argc    = 3
 * argv[0] = "./copy"
 * argv[1] = "1.txt"
 * argv[2] = "2.txt"
 */
int main(int argc, char **argv)
{
	int fd_old, fd_new;
	struct stat stat;
	char *buf;
	
	/* 1. 判断参数 */
	if (argc != 3) 
	{
		printf("Usage: %s <old-file> <new-file>\n", argv[0]);
		return -1;
	}

	/* 2. 打开老文件 */
	fd_old = open(argv[1], O_RDONLY);
	if (fd_old == -1)
	{
		printf("can not open file %s\n", argv[1]);
		return -1;
	}

	/* 3. 确定老文件的大小 */
	if (fstat(fd_old, &stat) == -1)
	{
		printf("can not get stat of file %s\n", argv[1]);
		return -1;
	}

	/* 4. 映射老文件 */
	buf = mmap(NULL, stat.st_size, PROT_READ, MAP_SHARED, fd_old, 0);
	if (buf == MAP_FAILED)
	{
		printf("can not mmap file %s\n", argv[1]);
		return -1;
	}

	/* 5. 创建新文件 */
	fd_new = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH);
	if (fd_new == -1)
	{
		printf("can not creat file %s\n", argv[2]);
		return -1;
	}

	/* 6. 写新文件 */
	if (write(fd_new, buf, stat.st_size) != stat.st_size)
	{
		printf("can not write %s\n", argv[2]);
		return -1;
	}

	/* 5. 关闭文件 */
	close(fd_old);
	close(fd_new);
	
	return 0;
}