Writing Custom Linux System Calls: A Complete Guide

Understanding the Syscall Mechanism

Most engineers never write a syscall, but understanding the mechanism teaches you more about kernel internals than reading documentation ever could. When Netflix needed microsecond-precise time measurements for CDN routing, they added a custom syscall. When PostgreSQL wanted zero-copy shared memory, they lobbied for new syscalls. The syscall boundary is where performance meets security, and getting it wrong crashes your kernel.