Note that Wayland doesn't have a full driver abstraction layer in userland like X does. Every Wayland compositior is expected to call into the Linux kernel driv

Note that Wayland doesn't have a full driver abstraction layer in userland like X does. Every Wayland compositior is expected to call into the Linux kernel drivers for the graphics card directly. GBM is just a thin wrapper that hides the fact that Linux never standardised the buffer creation interface across different hardware - it assumes that all those driver-specific interfaces wrap essentially the same shared Linux buffer management code, and it doesn't abstract stuff like modesetting at all. NVidia managed to reimplement enough of the Linux modesetting interface that existing code mostly works, but their own buffer management infrastructure is apparently different enough that they couldn't make it look like the one existing Wayland compositors are expecting to use. So they ended up creating their own slightly higher-level API instead.