这个系统调用需要shm_open返回的文件描述符，它返回指向内存的指针。
This system call requires the file descriptor from shm_open and returns a pointer to memory.
执行fork之后，父进程和子进程获得打开的所有文件描述符和数据值的拷贝，所以指针对于它们都是有效的。
After the fork, the parent and child have copies of all open file descriptors and data values, so the pointer works for both.
fd是文件描述符，是指向文件的一个指针。
fd is the file descriptor, a pointer to the file. For this example, use the following
通常可以把iocb看作AIO子系统使用的不透明数据结构。然而，如果需要文件描述符的structfile指针，可以通过iocb->ki_flip获取。
The iocb argument can usually be treated as an opaque cookie used by the AIO subsystem; if you need the struct file pointer for this file descriptor, however, you can find it as iocb->ki_filp.
程序代码只能访问头文件，该文件仅仅声明数据类型的描述符指针以及作用于该数据类型的操作。
The Protocol is described with DTD(Document Type Definition)style. We analyze the questions which should be paid attention to when designing such kind of application.
程序代码只能访问头文件，该文件仅仅声明数据类型的描述符指针以及作用于该数据类型的操作。
The Protocol is described with DTD(Document Type Definition)style. We analyze the questions which should be paid attention to when designing such kind of application.
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