ALL FILE I/O HANDLED IN PHP USERSPACE is processed through the PHP streams layer introduced with PHP 4.3. Internally, extension code might opt to use stdio or posix file handles to communicate with the local file system or berkeley domain sockets, or it might call into that same API used by userspace stream I/O.
The PHP Life Cycle
Variables from the Inside Out
Memory Management
Setting Up a Build Environment
Your First Extension
Returning Values
Accepting Parameters
Working with Arrays and HashTables
The Resource Data Type
PHP4 Objects
PHP5 Objects
Startup, Shutdown, and a Few Points in Between
INI Settings
Accessing Streams
Implementing Streams
Diverting the Stream
Configuration and Linking
Extension Generators
Setting Up a Host Environment
Advanced Embedding
Appendix A. A Zend API Reference
Appendix B. PHPAPI
Appendix C. Extending and Embedding Cookbook
Appendix D. Additional Resources