Linux Network I/O Model

    The Linux kernel treats all external devices as a file to operate, and the read and write operations on a file will call the system command provided by the kernel and return a file descriptor (fd, file descriptor). The reading and writing of a socket will also have a corresponding descriptor, called socketfd (socket descriptor). The descriptor is a number, which points to a structure in the kernel (file path, data area and other attributes).

    According to the classification of I/O models by UNIX network programming, UNIX provides five I/O models, as follows.
    (1) Blocking I/O model:



    (2) Non-blocking I/O model:


    (3) I/O multiplexing model:



    (4) Signal-driven I/O model:



    (5) Asynchronous I/O: