The mkdir systemcall creates the context, and the user process can subsequently open the associated files inside that directory.
mkdir系统调用用来创建这个上下文，用户进程然后可以打开这个目录中相关的文件。
2
This is done with the systemcall popen(), which can open to a pipe to another process, either for reading or writing.
这是用系统调用 popen() 完成的，它打开到另一个进程的管道以用于读或写。
3
This feature is implemented using the popen systemcall, which allows one process to open a pipe to another process, either for output or input. In this case we open a pipe to the command.