EINTR Interrupted system call 系统调用被禁止
Your write system call will be interrupted by the bus error signal SIGBUS, because you performed a bad memory access.
此时write系统调用会被进程接收到的SIGBUS信号中断，因为当前进程访问了非法内存地址。
By doing this the write system call returns with the number of bytes it wrote before it got interrupted and the errno set to success.
在这样处理方式下，write系统调用返回被信号中断前已写的字节数，并将errno全局变量设置为成功。
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