[kernel] Add endpoint object and related syscalls

The endpoint object adds synchronous IPC. Also added the wait-type of
'object' to threads.

src/kernel/objects/endpoint.cpp

@@ -0,0 +1,97 @@
+#include "objects/endpoint.h"
+#include "objects/thread.h"
+#include "page_manager.h"
+#include "scheduler.h"
+
+endpoint::endpoint() :
+	kobject(kobject::type::endpoint)
+{}
+
+endpoint::~endpoint()
+{
+	if (!check_signal(j6_signal_endpoint_closed))
+		close();
+}
+
+void
+endpoint::close()
+{
+	assert_signal(j6_signal_endpoint_closed);
+	for (auto &data : m_blocked)
+		data.th->wake_on_result(this, j6_status_closed);
+}
+
+j6_status_t
+endpoint::send(size_t len, void *data)
+{
+	scheduler &s = scheduler::get();
+	TCB *tcb = s.current();
+	thread_data sender = { thread::from_tcb(tcb), data };
+	sender.len = len;
+
+	if (!check_signal(j6_signal_endpoint_can_send)) {
+		assert_signal(j6_signal_endpoint_can_recv);
+		sender.th->wait_on_object(this);
+		m_blocked.append(sender);
+		s.schedule();
+
+		// we woke up having already finished the send
+		// because it happened in the receiver
+		return sender.th->get_wait_result();
+	}
+
+	thread_data receiver = m_blocked.pop_front();
+	if (m_blocked.count() == 0)
+		deassert_signal(j6_signal_endpoint_can_send);
+
+	j6_status_t status = do_message_copy(sender, receiver);
+
+	receiver.th->wake_on_result(this, status);
+	return status;
+}
+
+j6_status_t
+endpoint::receive(size_t *len, void *data)
+{
+	scheduler &s = scheduler::get();
+	TCB *tcb = s.current();
+	thread_data receiver = { thread::from_tcb(tcb), data };
+	receiver.len_p = len;
+
+	if (!check_signal(j6_signal_endpoint_can_recv)) {
+		assert_signal(j6_signal_endpoint_can_send);
+		receiver.th->wait_on_object(this);
+		m_blocked.append(receiver);
+		s.schedule();
+
+		// we woke up having already finished the recv
+		// because it happened in the sender
+		return receiver.th->get_wait_result();
+	}
+
+	thread_data sender = m_blocked.pop_front();
+	if (m_blocked.count() == 0)
+		deassert_signal(j6_signal_endpoint_can_recv);
+
+	// TODO: don't pop sender on some errors
+	j6_status_t status = do_message_copy(sender, receiver);
+	sender.th->wake_on_result(this, status);
+	return status;
+}
+
+j6_status_t
+endpoint::do_message_copy(const endpoint::thread_data &sender, endpoint::thread_data &receiver)
+{
+	if (sender.len > *receiver.len_p)
+		return j6_err_insufficient;
+
+	page_manager *pm = page_manager::get();
+	void *send_data = pm->get_offset_from_mapped(sender.data, sender.th->tcb()->pml4);
+	void *recv_data = pm->get_offset_from_mapped(receiver.data, receiver.th->tcb()->pml4);
+	kutil::memcpy(recv_data, send_data, sender.len);
+	*receiver.len_p = sender.len;
+
+	// TODO: this will not work if non-contiguous pages are mapped!!
+
+	return j6_status_ok;
+}

src/kernel/objects/endpoint.h

@@ -0,0 +1,53 @@
+#pragma once
+/// \file endpoint.h
+/// Definition of endpoint kobject types
+
+#include "j6/signals.h"
+#include "objects/kobject.h"
+
+/// Endpoints are objects that enable synchronous message-passing IPC
+class endpoint :
+	public kobject
+{
+public:
+	endpoint();
+	virtual ~endpoint();
+
+	/// Close the endpoint, waking all waiting processes with an error
+	void close();
+
+	/// Check if the endpoint has space for a message to be sent
+	inline bool can_send() const { return check_signal(j6_signal_endpoint_can_send); }
+
+	/// Check if the endpoint has a message wiating already
+	inline bool can_receive() const { return check_signal(j6_signal_endpoint_can_recv); }
+
+	/// Send a message to a thread waiting to receive on this endpoint. If no threads
+	/// are currently trying to receive, block the current thread.
+	/// \arg len   The size in bytes of the message
+	/// \arg data  The message data
+	/// \returns   j6_status_ok on success
+	j6_status_t send(size_t len, void *data);
+
+	/// Receive a message from a thread waiting to send on this endpoint. If no threads
+	/// are currently trying to send, block the current thread.
+	/// \arg len   [in] The size in bytes of the buffer [out] Number of bytes in the message
+	/// \arg data  Buffer for copying message data into
+	/// \returns   j6_status_ok on success
+	j6_status_t receive(size_t *len, void *data);
+
+private:
+	struct thread_data
+	{
+		thread *th;
+		void *data;
+		union {
+			size_t *len_p;
+			size_t len;
+		};
+	};
+
+	j6_status_t do_message_copy(const thread_data &sender, thread_data &receiver);
+
+	kutil::vector<thread_data> m_blocked;
+};

src/kernel/objects/kobject.h

@@ -20,6 +20,7 @@ public:
 		event,
 		eventpair,
 		channel,
+		endpoint,
 
 		vms,
 		vmo,

src/kernel/objects/thread.cpp

@@ -56,6 +56,14 @@ thread::wait_on_time(uint64_t t)
 	clear_state(state::ready);
 }
 
+void
+thread::wait_on_object(kobject *o)
+{
+	m_wait_type = wait_type::object;
+	m_wait_data = reinterpret_cast<uint64_t>(o);
+	clear_state(state::ready);
+}
+
 bool
 thread::wake_on_signals(kobject *obj, j6_signal_t signals)
 {
@@ -86,6 +94,20 @@ thread::wake_on_time(uint64_t now)
 	return true;
 }
 
+bool
+thread::wake_on_object(kobject *o)
+{
+	if (m_wait_type != wait_type::object ||
+		reinterpret_cast<uint64_t>(o) != m_wait_data)
+		return false;
+
+	m_wait_type = wait_type::none;
+	m_wait_result = j6_status_ok;
+	m_wait_obj = o->koid();
+	set_state(state::ready);
+	return true;
+}
+
 void
 thread::wake_on_result(kobject *obj, j6_status_t result)
 {

src/kernel/objects/thread.h

@@ -35,7 +35,7 @@ class thread :
 	public kobject
 {
 public:
-	enum class wait_type : uint8_t { none, signal, time };
+	enum class wait_type : uint8_t { none, signal, time, object };
 	enum class state : uint8_t {
 		ready    = 0x01,
 		loading  = 0x02,
@@ -78,6 +78,10 @@ public:
 	/// \arg t  Clock value to wait for
 	void wait_on_time(uint64_t t);
 
+	/// Block the thread, waiting on the given object
+	/// \arg o  The ojbect that should wake this thread
+	void wait_on_object(kobject *o);
+
 	/// Wake the thread if it is waiting on signals.
 	/// \arg obj     Object that changed signals
 	/// \arg signals Signal state of the object
@@ -89,6 +93,11 @@ public:
 	/// \returns  True if this action unblocked the thread
 	bool wake_on_time(uint64_t now);
 
+	/// Wake the thread if it is waiting on the given object.
+	/// \arg o  Object trying to wake the thread
+	/// \returns  True if this action unblocked the thread
+	bool wake_on_object(kobject *o);
+
 	/// Wake the thread with a given result code.
 	/// \arg obj     Object that changed signals
 	/// \arg result  Result code to return to the thread

src/kernel/page_manager.cpp

@@ -153,6 +153,30 @@ page_manager::map_offset_pointer(void **pointer, size_t length)
 	*pointer = kutil::offset_pointer(*pointer, page_offset);
 }
 
+void *
+page_manager::get_offset_from_mapped(void *p, page_table *pml4)
+{
+	if (!pml4) pml4 = get_pml4();
+	uintptr_t v = reinterpret_cast<uintptr_t>(p);
+
+	page_table_indices idx{v};
+	page_table *tables[4] = {pml4, nullptr, nullptr, nullptr};
+
+	for (int i = 1; i < 4; ++i) {
+		tables[i] = tables[i-1]->get(idx[i-1]);
+		if (!tables[i])
+			return nullptr;
+	}
+
+	uintptr_t a = tables[3]->entries[idx[3]];
+	if (!(a & 1))
+		return nullptr;
+
+	return offset_virt(
+			(a & ~0xfffull) |
+			(v & 0xfffull));
+}
+
 void
 page_manager::dump_pml4(page_table *pml4, bool recurse)
 {

src/kernel/page_manager.h

@@ -101,6 +101,11 @@ public:
 		return kutil::offset_pointer(reinterpret_cast<void *>(a), memory::page_offset);
 	}
 
+	/// Get the offet-mapped virtual address of a normal virtual address
+	/// \arg p   Virtual address
+	/// \returns Virtual address in offset-mapped linear space
+	void * get_offset_from_mapped(void *p, page_table *pml4 = nullptr);
+
 	/// Dump the given or current PML4 to the console
 	/// \arg pml4     The page table to use, null for the current one
 	/// \arg recurse  Whether to print sub-tables

src/kernel/syscalls/endpoint.cpp

@@ -0,0 +1,99 @@
+#include "j6/errors.h"
+#include "j6/types.h"
+
+#include "log.h"
+#include "objects/endpoint.h"
+#include "objects/process.h"
+#include "scheduler.h"
+
+namespace syscalls {
+
+j6_status_t
+endpoint_create(j6_handle_t *handle)
+{
+	scheduler &s = scheduler::get();
+	TCB *tcb = s.current();
+	thread *parent = thread::from_tcb(tcb);
+	process &p = parent->parent();
+
+	endpoint *e = new endpoint;
+	*handle = p.add_handle(e);
+
+	return j6_status_ok;
+}
+
+j6_status_t
+endpoint_close(j6_handle_t handle)
+{
+	scheduler &s = scheduler::get();
+	TCB *tcb = s.current();
+	thread *parent = thread::from_tcb(tcb);
+	process &p = parent->parent();
+
+	kobject *o = p.lookup_handle(handle);
+	if (!o || o->get_type() != kobject::type::endpoint)
+		return j6_err_invalid_arg;
+
+	p.remove_handle(handle);
+	endpoint *e = static_cast<endpoint*>(o);
+	e->close();
+
+	return j6_status_ok;
+}
+
+j6_status_t
+endpoint_send(j6_handle_t handle, size_t len, void *data)
+{
+	scheduler &s = scheduler::get();
+	TCB *tcb = s.current();
+	thread *parent = thread::from_tcb(tcb);
+	process &p = parent->parent();
+
+	kobject *o = p.lookup_handle(handle);
+	if (!o || o->get_type() != kobject::type::endpoint)
+		return j6_err_invalid_arg;
+
+	endpoint *e = static_cast<endpoint*>(o);
+	j6_status_t status = e->send(len, data);
+	return status;
+}
+
+j6_status_t
+endpoint_receive(j6_handle_t handle, size_t *len, void *data)
+{
+	scheduler &s = scheduler::get();
+	TCB *tcb = s.current();
+	thread *parent = thread::from_tcb(tcb);
+	process &p = parent->parent();
+
+	kobject *o = p.lookup_handle(handle);
+	if (!o || o->get_type() != kobject::type::endpoint)
+		return j6_err_invalid_arg;
+
+	endpoint *e = static_cast<endpoint*>(o);
+	j6_status_t status = e->receive(len, data);
+	return status;
+}
+
+j6_status_t
+endpoint_sendrecv(j6_handle_t handle, size_t *len, void *data)
+{
+	scheduler &s = scheduler::get();
+	TCB *tcb = s.current();
+	thread *parent = thread::from_tcb(tcb);
+	process &p = parent->parent();
+
+	kobject *o = p.lookup_handle(handle);
+	if (!o || o->get_type() != kobject::type::endpoint)
+		return j6_err_invalid_arg;
+
+	endpoint *e = static_cast<endpoint*>(o);
+	j6_status_t status = e->send(*len, data);
+	if (status != j6_status_ok)
+		return status;
+
+	status = e->receive(len, data);
+	return status;
+}
+
+} // namespace syscalls