3.17. Summary

This chapter has described the basic I/O functions provided by the UNIX System. These are often called the unbuffered I/O functions because each read or write invokes a system call into the kernel. Using only read and write, we looked at the effect of various I/O sizes on the amount of time required to read a file. We also looked at several ways to flush written data to disk and their effect on application performance.

Atomic operations were introduced when multiple processes append to the same file and when multiple processes create the same file. We also looked at the data structures used by the kernel to share information about open files. We'll return to these data structures later in the text.

We also described the ioctl and fcntl functions. We return to both of these functions in Chapter 14, where we'll use ioctl with the STREAMS I/O system, and fcntl for record locking.