Open Source Summit + Embedded Linux Conference + OSPOCon 2021

Ever wondered why so many of the popular plumbing-layer user-space libraries are usually called libfoobar2, gstreamer1.0 etc.? Why we have cgroup and crgroup2? Why a lot of kernel uAPI headers define SOMETHING_SOMETHING_IOCTL_V2? Unlike the in-kernel interfaces, user-space libraries usually promise a certain level of stability of the API and ABI - especially across a single major release. The kernel is even more strict on that - user-space programs must not be broken with incompatible changes to the kernel uAPI and it's extremely rare to see any kernel interface modified or removed. This presentation will try to answer the question: why is it so difficult to design new programming interfaces correctly the first time? Why are minor, backward-compatible changes often not enough to address design issues and why do we need to always "plan to throw one away"? The author has hands-on experience with this problem - having helped design the GPIO uAPI and developed the user-space part of the kernel interface, only to see the kernel interface redesigned and ending up working on version 2 of the userland library. This presentation hopes to shed light on the aspects of good API design and help programmers avoid having to release multiple major versions of their open-source projects.