Initial priority-based scheduler

- Scheduler now has multiple linked_lists of processes at different
  priorities
- Process structure improvements
- scheduler::tick() and scheduler::schedule() separation

src/kernel/scheduler.h

@@ -1,25 +1,57 @@
 #pragma once
 /// \file scheduler.h
 /// The task scheduler and related definitions
+#include "kutil/enum_bitfields.h"
+#include "kutil/linked_list.h"
 #include "kutil/memory.h"
+#include "kutil/slab_allocator.h"
 #include "kutil/vector.h"
 
 class lapic;
 struct page_table;
+struct cpu_state;
 
+extern "C" addr_t isr_handler(addr_t, cpu_state);
+
+enum class process_flags : uint32_t
+{
+	running   = 0x00000001,
+	ready     = 0x00000002,
+	loading   = 0x00000004,
+
+	const_pri = 0x80000000,
+
+	none      = 0x00000000
+};
+IS_BITFIELD(process_flags);
 
 struct process
 {
-	uint16_t pid;
+	uint32_t pid;
+	uint32_t ppid;
+
+	uint8_t priority;
+
+	uint8_t reserved0;
+	uint16_t reserved;
+
+	process_flags flags;
+
 	addr_t rsp;
 	page_table *pml4;
 };
 
+using process_list = kutil::linked_list<process>;
+using process_node = process_list::item_type;
+using process_slab = kutil::slab_allocator<process>;
 
 /// The task scheduler
 class scheduler
 {
 public:
+	static const uint8_t num_priorities = 8;
+	static const uint8_t default_priority = num_priorities / 2;
+
 	/// Constructor.
 	/// \arg apic  Pointer to the local APIC object
 	scheduler(lapic *apic);
@@ -34,20 +66,34 @@ public:
 	/// timer interrupts or other preemption methods.
 	void start();
 
-	/// Handle a timer tick
+	/// Run the scheduler, possibly switching to a new task
 	/// \arg rsp0  The stack pointer of the current interrupt handler
-	/// \returns   The stack pointer to handler to switch to
-	addr_t tick(addr_t rsp0);
+	/// \returns   The stack pointer to switch to
+	addr_t schedule(addr_t rsp0);
+
+	/// Get the current process.
+	/// \returns  A pointer to the current process' process struct
+	inline process * current() { return m_current; }
 
 	/// Get a reference to the system scheduler
 	/// \returns  A reference to the global system scheduler
 	static scheduler & get() { return s_instance; }
 
 private:
+	friend addr_t isr_handler(addr_t, cpu_state);
+
+	/// Handle a timer tick
+	/// \arg rsp0  The stack pointer of the current interrupt handler
+	/// \returns   The stack pointer to switch to
+	addr_t tick(addr_t rsp0);
+
 	lapic *m_apic;
-	kutil::vector<process> m_processes;
-	uint16_t m_current;
-	uint16_t m_next_pid;
+
+	uint32_t m_next_pid;
+
+	process_node *m_current;
+	process_slab m_process_allocator;
+	process_list m_runlists[num_priorities];
 
 	static scheduler s_instance;
 };