> One big challenge it addresses is Linux’s driver problem
Android devices have been plagued with vendors having out-of-tree device drivers that compile for linux 3.x, but not 4.x or 5.x, and so the phone is unable to update to a new major android version wit ha new linux kernel.
A micro-kernel with a clearly defined device driver API would mean that Google could update the kernel and android version, while continuing to let old device drivers work without update.
That's consistently been one of the motivating factors cited, and linux's monolithic design, where the internal driver API has never been anything close to stable, will not solve that problem.
A monolithic kernel with a clearly defined device driver API would do the same thing. Linux is explicitly not that, of course. Maintaining backwards-compatibility in an API is a non-trivial amount of work regardless of whether the boundary is a network connection, IPC, or function call.
Maybe, but I doubt it. History has shown pretty clearly that driver authors will write code that takes advantage of its privilege state in a monolithic kernel to bypass the constraints of the driver API. Companies will do this to kludge around the GPL, to make their Linux driver look more like the Windows driver, because they were lazy and it was easier than doing it right, and for any number of other reasons. The results include the drivers failing if you look at the rest of the system funny and making the entire system wildly insecure.
If you want to a driver not subject to competent code review abide by the terms of the box in which it lives, then the system needs to strictly enforce the box. Relying on a header file with limited contents will not do the job.
Well, your job is shipping the driver. If the API is limited and/or your existing drivers in Windows or other OSs do something and the linux driver doesn't then you have a problem
Linux kernel pros: it evolves organically
Linux kernel cons: it evolves organically
However, if you discover that the box was insufficient at any point, you have to choose between changing the box (and breaking some perfectly good drivers), or leaving the insufficient box in place. API versioning can let you delay this decision to reduce pain, but it will happen at some point.
FWIW, I'm hugely in favor of microkernels, but they are a lead bullet (which we need lots of), not a silver bullet for these sorts of problems.
What's preventing adding a driver compatibility layer over the unstable API? I would accept a some performance cost and NOPs for new features using a shim for existing legacy binary drivers compared to being forced to junk functioning hardware.
Android using the absolutely most head or tip version of the Linux kernel sounds like a QA nightmare of its own.
Mobile SOC has to have everything to start up the phone, as there is no bios like system that the driver is kind work through. Maybe this is a problem that could be solved, but it hasn't been yet.
