mmap映射文件的时候出现错误，提示no such device，求大神指导。

[没有壳的snail]

用mmap把一个字符设备文件映射到内存中，结果出现错误，字符设备文件是存在的，也是可以打开的，请问各位大神是什么问题，代码如下。

#define print_tty "/dev/ttyS2"


int main(int argc, char **argv)
{	
	int scan_fd,fd,seri_fd;
	char s[32] = {0};
	pthread_t thread;
	FILE *fp = NULL;
	int on = 1;
	unsigned long mmap_size, mmap_addr,addr_seri,size_seri;
	int mmap_addr_fd = -1;
	char *mmap_addr_seri;
	
		//打印机全局变量和共享内存初始化
		seri_fd = open(print_tty, O_RDWR);	
		if(seri_fd < 0)	
		{		
			perror("open");		
			close(mmap_addr_fd);
			return (-1);	
		}

		scan_fd = open("/dev/scanner", O_RDWR);
		
		
		
		if(scan_fd < 0)	
		{		
			perror("open");		
			close(mmap_addr_fd);
			close(seri_fd);
			return (-1);	
		}

		fd = open("/proc/memshare/phymem_addr", O_RDONLY);	
		if(fd < 0)	
		{		
			printf("cannot open phymem_addr\n");	
			close(mmap_addr_fd);
			close(seri_fd);
			close(scan_fd);
			return -1;
		}	
		read(fd, s, sizeof(s));	
		sscanf(s, "%lx", &addr_seri);
		close(fd);

		fd = open("/proc/memshare/phymem_size", O_RDONLY);
		if(fd < 0)	
		{		
			printf("cannot open phymem_size\n");	
			close(mmap_addr_fd);
			close(seri_fd);
			close(scan_fd);
			return -1;	
		}	
		read(fd, s, sizeof(s));	
		sscanf(s, "%lu", &size_seri);
		close(fd);
		
		printf("addr_seri=%lx-------size_seri=%lu\n",addr_seri,size_seri);

		mmap_addr_seri = mmap(0, size_seri, PROT_READ, MAP_SHARED, scan_fd, addr_seri);	
		if((char *)mmap_addr_seri == NULL)	
		{		
			printf("no data in sharemem\n");	
			close(mmap_addr_fd);
			close(seri_fd);
			close(scan_fd);
			return -1;
		}
		
		if(mmap_addr_seri == (void *)(-1))
		{
			perror("mmap error");
		}
			
		printf("mmap_addr_seri------------%x\n",mmap_addr_seri);
}

[zhxianbin]

“不是所有的设备都能进行mmap抽象，比如像串口和其他面向流的设备就不能做mmap抽象” http://www.cnblogs.com/geneil/archive/2011/12/08/2281222.html