System Ipaw O model
Synchronization: after the process sends a request call to the kernel, the kernel does not actively return status information to the process, and the process needs to ask the kernel actively after a period of time.
Async: after the process sends a request call to the kernel, the kernel actively returns the invocation state to the process after completion.
Blocking: after a request call in user space is initiated, the caller will not process any other requests until the request call ends.
Non-blocking: after the user space request call is initiated, the caller can process other requests.
