Initial process waiting/waking

Processes can now wait on signals/children/time. There is no clock
currently so "time" is just a monotonically increating tick count. Added
a SLEEP syscall to test this waiting/waking.

src/kernel/process.h

@@ -0,0 +1,81 @@
+#pragma once
+/// \file process.h
+/// The processes and related definitions
+#include "kutil/enum_bitfields.h"
+#include "kutil/linked_list.h"
+#include "kutil/memory.h"
+#include "page_manager.h"
+
+
+enum class process_flags : uint32_t
+{
+	running   = 0x00000001,
+	ready     = 0x00000002,
+	loading   = 0x00000004,
+
+	const_pri = 0x80000000,
+
+	none      = 0x00000000
+};
+IS_BITFIELD(process_flags);
+
+enum class process_wait : uint8_t
+{
+	none,
+	signal,
+	child,
+	time
+};
+
+/// A process
+struct process
+{
+	uint32_t pid;
+	uint32_t ppid;
+
+	process_flags flags;
+
+	uint16_t reserved0;
+
+	uint8_t priority;
+
+	process_wait waiting;
+	uint64_t waiting_info;
+
+	uint32_t return_code;
+
+	uint32_t reserved1;
+
+	addr_t rsp;
+	page_table *pml4;
+
+	/// Unready this process until it gets a signal
+	/// \arg sigmask  A bitfield of signals to wake on
+	void wait_on_signal(uint64_t sigmask);
+
+	/// Unready this process until a child exits
+	/// \arg pid  PID of the child to wait for, or 0 for any
+	void wait_on_child(uint32_t pid);
+
+	/// Unready this process until after the given time
+	/// \arg time  The time after which to wake
+	void wait_on_time(uint64_t time);
+
+	/// If this process is waiting on the given signal, wake it
+	/// \argument signal  The signal sent to the process
+	/// \returns  True if this wake was handled
+	bool wake_on_signal(int signal);
+
+	/// If this process is waiting on the given child, wake it
+	/// \argument child  The process that exited
+	/// \returns  True if this wake was handled
+	bool wake_on_child(process *child);
+
+	/// If this process is waiting on a time, check it
+	/// \argument now  The current time
+	/// \returns  True if this wake was handled
+	bool wake_on_time(uint64_t now);
+};
+
+using process_list = kutil::linked_list<process>;
+using process_node = process_list::item_type;