ERRNO错误

单纯记录一下：
EFAULT:
It happen if the memory address of some argument passed to sendto (or more generally to any system call) is invalid. Think of it as a sort of SIGSEGV in kernel land regarding your syscall. For instance, if you pass a null or invalid buffer pointer (for reading, writing, sending, recieving…)。说明在对套接字上调用某些函数的时候传入了空指针等非法参数，的确如此。