mac下读取优盘数据报错

[good_cyg]

在mac 10.10.5下

int main(void)
{
FILE *f;
char block[512]={0};
int r;
char* fileName2="/dev/disk2";
f = fopen(fileName2, "rb");
if (f == NULL) {
printf("error:%s open is null \n", fileName2);
return -1;
}

r = fread(block, 1, sizeof(block), f);
return 0;
}
int main(void)
{
FILE *f;
char block[512]={0};
int r;
char* fileName2="/dev/disk2s1“;
f = fopen(fileName2, "rb");
if (f == NULL) {
printf("error:%s open is null \n", fileName2);
return -1;
}

r = fread(block, 1, sizeof(block), f);
return 0;
}

两种写法发现f=null，也就是fopen打开失败了。求大神指点？