There are two types of Application programming interface (API) in the Linux kernel that are not to be confused: "user-kernel" API and "in-kernel" API.
User-kernel API
The User-kernel API is the API that allows programs in user-space to access system resources and services of the Linux kernel. This API, by choice, never breaks. The POSIX API is only a small part of the Linux kernel API.
Many available free and open-source software is written with the POSIX API. But since the last POSIX version is from 2008, and since so much more development is going on with the Linux kernel as compared to the other POSIT-compatible kernel, more programs pop up, that are written with the Linux kernel API in mind. Well-known examples are systemd and Weston.
People like e.g. Lennart Poettering openly advocate to write software for the Linux kernel API instead of POSIX, where this offers advantages.
In-kernel API
By choice, the Linux kernel has no in-kernel API (a.k.a. Binary Kernel Interface.[1]
References
External links
- The API of Linux kernel 2.6.20 – sadly no current version available
- The Linux Programming Interface
- Interactive Linux kernel map with main API functions and structures
- Linux Device Drivers by Jonathan Corbet, Greg Kroah-Hartman and Alessandro Rubini, 3rd edition
- Linux Kernel Linked List Explained
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