feat: scheduling, usermode, shell

kernel/src/Sched/Scheduler.hpp

@@ -0,0 +1,59 @@
+/*
+    * Scheduler.hpp
+    * Preemptive process scheduler with user-mode support
+    * Copyright (c) 2025 Daniel Hammer
+*/
+
+#pragma once
+#include <cstdint>
+
+namespace Sched {
+
+    static constexpr int MaxProcesses = 16;
+    static constexpr uint64_t StackPages = 4;  // 16 KiB kernel stack per process
+    static constexpr uint64_t StackSize = StackPages * 0x1000;
+    static constexpr uint64_t UserStackPages = 4;  // 16 KiB user stack
+    static constexpr uint64_t UserStackSize = UserStackPages * 0x1000;
+    static constexpr uint64_t UserStackTop = 0x7FFFFFF000ULL;  // User stack top VA
+    static constexpr uint64_t UserHeapBase = 0x40000000ULL;    // User heap start VA
+    static constexpr uint64_t ExitStubAddr = 0x3FF000ULL;     // User-space exit stub page
+    static constexpr uint64_t TimeSliceMs = 10; // 10 ms time slice
+
+    enum class ProcessState {
+        Free,
+        Ready,
+        Running,
+        Terminated
+    };
+
+    struct Process {
+        int pid;
+        ProcessState state;
+        const char* name;
+        uint64_t savedRsp;
+        uint64_t stackBase;       // Bottom of allocated kernel stack (lowest address)
+        uint64_t entryPoint;
+        uint64_t sliceRemaining;  // Ticks left in current time slice
+        uint64_t pml4Phys;        // Physical address of per-process PML4
+        uint64_t kernelStackTop;  // Top of kernel stack (for TSS RSP0 / SYSCALL)
+        uint64_t userStackTop;    // User-space stack top
+        uint64_t heapNext;        // Simple bump allocator for user heap
+    };
+
+    void Initialize();
+    void Spawn(const char* vfsPath);
+    void Schedule();
+
+    // Called from the APIC timer handler on every tick.
+    void Tick();
+
+    // Get the PID of the currently running process (-1 if idle)
+    int GetCurrentPid();
+
+    // Get a pointer to the currently running process (nullptr if idle)
+    Process* GetCurrentProcessPtr();
+
+    // Called by terminated processes to mark themselves done
+    void ExitProcess();
+
+}