> On a microkernel you'd just be writing any other user process, with access to a couple of ports and and maybe a special hook to handle hw interrupts This is

> On a microkernel you'd just be writing any other user process, with access to a couple of ports and and maybe a special hook to handle hw interrupts This is a fiction. Hint: if a "user process" can wreak havoc on the system simply by misbehaving (in a way that may or may not be malicious), as drivers interacting with low-level hardware can, it's not a user process in practice, and should not be understood as one. The whole point of making that kernel vs. user space distinction in the first place is so that user programs can't wreak havoc on the system. There are plenty of things that can and should be done in userland (and oftentimes they are, see e.g. Plan9), but drivers are not among these unless you can always rely on something like IOMMU to make sure that the hardware cannot be made to misbehave in a way that affects security guarantees.