A user-space process can now touch real hardware directly, capability-gated by
the device tree — the microkernel driver model.
- src/kernel/devsvc.zig: flattens the discovered device tree into an
id-indexed snapshot + a claim table at boot (devsvc.init from main.zig).
- Syscalls 11-13: dev_enumerate (snapshot the table), dev_claim (take
exclusive ownership), mmio_map (map a claimed device's MMIO window into the
caller's AS and return the register base). The claim is the capability:
mmio_map refuses any device the caller doesn't own.
- paging.mapUserDeviceInto: maps device MMIO strong-uncacheable (PCD|PWT) and
marks each leaf with a device_grant PTE bit; freeSubtree skips pmm.free on
those leaves, so tearing down a driver never returns MMIO frames to the RAM
pool (the teardown hazard). MMIO grants live in a distinct arena, PML4[226]
(Task.dev_map_next), so device pages widen no kernel mapping.
- lib/dev.zig: user enumerate/claim/mmioMap wrappers; shared DeviceDesc/ResDesc
in danos (root.zig). sbin/hpetd.zig: finds the HPET, claims it, maps its
registers, enables the counter (an MMIO write) and reads it (0xF0) — proving
read+write passthrough to real hardware.
- Tests: `hpet` (driver reads the counter advancing from ring 3) and `iopass`
(device-granted frame survives address-space teardown). Suite 33/33.
irq_bind/irq_ack (IRQ-as-message) are stubbed (-1) pending; notifyFromIsr (M7)
is the hook they'll use.
