Refactor the scheduler so all scheduleable work is wrapped in Arc<Work>,
replacing the previous per-CPU wait_q design where sleeping tasks were
bound to a specific CPU. Wakers now hold direct Arc<Work> references and
can re-enqueue tasks on any CPU upon wakeup.
Key changes:
- Add Work struct wrapping OwnedTask with an AtomicTaskState and
scheduler metadata (SchedulerData), replacing the old SchedulableTask.
Remove Task::state (Arc<SpinLock<TaskState>>). Work::state is now the
single source of truth for task state.
- Rewrite the run queue using BinaryHeap-based eligible/ineligible split
(EEVDF) with a dedicated VClock, replacing the BTreeMap linear scan.
Extract vclock into its own module.
- Rewrite wakers to hold Arc<Work> directly instead of looking up tasks
by TaskDescriptor from TASK_LIST.
- Replace lock-based sleep transitions in uspc_ret with atomic CAS
(try_sleep_current) that correctly detects concurrent Woken state.
- Simplify least-tasked-CPU metric to use only run-queue weight, since
sleeping tasks are no longer bound to any CPU.
- Add current_work() accessor.
If multiple drivers are associated with a compatible string, don't
override an existing probe_fn. Instead, store a list of associated
probe_fns. Once a probe_fn has claimed the device stop calling the
associated probe chain.
Add a virtio-rng entropy source driver that registers with the kernel
RNG subsystem. Introduce `ProbeError::NoMatch` so virtio drivers can
silently reject empty or wrong-type MMIO slots without spamming the boot
log with fatal errors or leaving devices stuck in the deferred queue.
Replace the single `SmallRng` with a proper two-layer RNG architecture:
- Global BLAKE2s-256 entropy pool that accumulates entropy and gates
seed extraction behind a 256-bit threshold.
- Per-CPU ChaCha20Rng instances that are lazily seeded from the pool on
first use and periodically reseed every 1 MB by XOR-ing a fresh BLAKE2
extract with 32 bytes of their own output.
The /dev/random chardev uses fill_random_bytes directly instead of
routing through the syscall layer.
