The Poplar Kernel

At the core of Poplar is a small Rust microkernel. The kernel's job is to multiplex access to hardware resources (such as CPU time, memory, and peripherals) between competing bits of userspace code.

Poplar is a microkernel because its drivers, pieces of code for managing the many different devices a computer may have, live in userspace, and are relatively unpriviledged compared to the kernel. This provides safety benefits over a monolithic kernel because a misbehaving or malicious driver (supplied by a hardware vendor, for example) has a much more limited scope of operation. The disadvantage is that microkernels tend to be slower than monolithic kernels, due to increased overheads of communication between the kernel and userspace.

Kernel objects

The Poplar microkernel is object-based - resources managed by the kernel are represented as discrete 'objects', and are interacted with from userspace via plain integers called 'handles'. Multiple handles referring to a single object can exist, and each possesses a set of permissions that dictate how the owning task can interact with the object.

Kernel objects are used for:

• Task creation and management (e.g. AddressSpace and Task)
• Access to hardware resources (e.g. MemoryObject)
• Message passing between tasks (e.g. Channel)
• Signaling and waiting (e.g. Event)