The Linux Programming Interface

13FILE I/O BUFFERING

In the interests of speed and efficiency, I/O system calls (i.e., the kernel) and the I/O functions of the standard C library (i.e., the stdio functions) buffer data when operating on disk files. In this chapter, we describe both types of buffering and consider how they affect application performance. We also look at various techniques for influencing and disabling both types of buffering, and look at a technique called direct I/O, which is useful for bypassing kernel buffering in certain circumstances.

13.1 Kernel Buffering of File I/O: The Buffer Cache

When working with disk files, the read() and write() system calls don’t directly initiate disk access. Instead, they simply copy data between a user-space buffer and a buffer ...