UNIX Filesystems: Evolution, Design, and Implementation

The Standard I/O Library

Many users require functionality above and beyond what is provided by the basic file access system calls. The standard I/O library, which is part of the ANSI C standard, provides this extra level of functionality, avoiding the need for duplication in many applications.

There are many books that describe the calls provided by the standard I/O library (stdio). This chapter offers a different approach by describing the implementation of the Linux standard I/O library showing the main structures, how they support the functions available, and how the library calls map onto the system call layer of UNIX.

The needs of the application will dictate whether the standard I/O library will be used as opposed to basic file-based system calls. If extra functionality is required and performance is not paramount, the standard I/O library, with its rich set of functions, will typically meet the needs of most programmers. If performance is key and more control is required over the execution of I/O, understanding how the filesystem performs I/O and bypassing the standard I/O library is typically a better choice.

Rather than describing the myriad of stdio functions available, which are well documented elsewhere, this chapter provides an overview of how the standard I/O library is implemented. For further details on the interfaces available, see Richard Steven's book Advanced ...