iris/invoke.ccp

#pypp 0
// Iris: micro-kernel for a capability-based operating system.
// invoke.ccp: Capability invocation and kernel responses.
// Copyright 2009 Bas Wijnen <wijnen@debian.org>
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

#include "kernel.hh"

void kThread::raise (unsigned code, unsigned data):
	panic (code, "raise")
	dbg_log ("raise ")
	dbg_log_num ((unsigned)current)
	dbg_log_char ('/')
	if code < NUM_EXCEPTION_CODES:
		dbg_log (exception_name[code])
	else:
		dbg_log ("invalid code:")
		dbg_log_num (code)
	dbg_log_char ('/')
	dbg_log_num (data)
	dbg_log_char ('\n')
	unrun ()
	if slots < 1 || !caps[0] || !caps[0]->cap (0)->target:
		return
	kCapability::Context c
	c.caps = NULL
	c.data[0] = Num (code, data)
	c.data[1] = 0
	caps[0]->cap (0)->invoke (&c)

// From user-provided, thus untrusted, data, find a capability.
kCapRef kThread::find_capability (unsigned code, bool *copy):
	*copy = code & CAP_COPY
	unsigned c = code & ~CAP_COPY
	unsigned slot = c >> 16
	unsigned num = c & 0xffff
	if slot >= slots || !caps[slot] || num >= caps[slot]->size:
		if c != CAP_NONE:
			panic (code, "debug")
			dbg_log_num ((unsigned)old_current)
			dbg_log (": invalid capability ")
			dbg_log_num (code)
			dbg_log_char ('\n')
		return kCapRef ()
	return kCapRef (caps[slot], num)

void kThread::fill_slot (unsigned slot, kCaps *new_caps):
	if slot >= slots:
		return
	if caps[slot]:
		// TODO: invalidate slot.
	caps[slot] = new_caps
	if new_caps:
		// TODO: link it into a list.

// Try to deliver a message.
bool kReceiver::try_deliver ():
	if !messages:
		return false
	if !owner || !owner->is_waiting ():
		return false
	kMessage *m = last_message
	if protected_only:
		for ; m; m = (kMessage *)m->prev:
			if m->cap_protected.value () == reply_protected_data.value ():
				protected_only = false
				break
		if !m:
			return false
	owner->fill_slot (owner->recv_slot, m->caps)
	kThread_arch_receive (owner, m->cap_protected, recv_protected, m->data)
	address_space->free_message (this, m)
	owner->unwait ()
	return true

// Send a message to a receiver; try to deliver it immediately.
bool kReceiver::send_message (Num cap_protected, kCapability::Context *c):
	if owner && owner->is_waiting () && (cap_protected.value () == reply_protected_data.value () || !protected_only):
		if protected_only:
			protected_only = false
		if owner->recv_slot < owner->slots:
			owner->fill_slot (owner->recv_slot, c->caps)
		kThread_arch_receive (owner, cap_protected, recv_protected, c->data)
		owner->unwait ()
		return true
	// The owner was not waiting, or it was not possible to deliver the message.  Put it in the queue.
	kMessage *msg = NULL;
	if queue_limit:
		msg = address_space->alloc_message (this)
		if msg:
			--queue_limit
	if !msg:
		// TODO: use sender-provided storage.
	if !msg:
		return false
	msg->cap_protected = cap_protected
	if protected_only && cap_protected.value () == reply_protected_data.value ():
		// Put this message in the end (where it will be first seen).  Clear the protected_only flag.
		protected_only = false
		if msg->next:
			((kMessage *)msg->next)->prev = NULL
			messages = (kMessage *)msg->next
			msg->next = NULL
			msg->prev = last_message
			((kMessage *)msg->prev)->next = msg
			last_message = msg
	for unsigned i = 0; i < 2; ++i:
		msg->data[i] = c->data[i]
	msg->caps = c->caps
	return true

static kCapRef reply
static kReceiver *reply_target
static Num reply_protected

static void reply_num (unsigned num1, unsigned num2 = 0, unsigned num3 = 0):
	kCapability::Context c
	c.data[0] = Num (num1, num2)
	c.data[1] = num3
	c.caps = NULL
	invoke (reply_target, reply_protected, &c, NULL)

static void reply_cap (unsigned target, Num cap_protected, kCapRef *ref):
	if reply:
		reply.set ((kReceiver *)target, cap_protected, kCapRef (), ref)
	reply_num (0)

static void receiver_invoke (unsigned cmd, unsigned target, Num cap_protected, kCapability::Context *c):
	kReceiver *receiver = (kReceiver *)cap_protected.l
	switch cmd:
		case Receiver::SET_OWNER:
			if c->caps->size < 2:
				reply_num (~0)
				return
			unsigned cap = (unsigned)c->caps->cap (1)->target
			if cap != (CAPTYPE_THREAD | CAP_MASTER) && cap != (CAPTYPE_THREAD | Thread::SET_OWNER):
				// FIXME: This makes it impossible to use a fake kThread capability.
				return
			receiver->own ((kThread *)c->caps->cap (1)->cap_protected.l)
			break
		case Receiver::CREATE_CAPABILITY:
			reply_cap ((unsigned)receiver, c->data[1], &receiver->capabilities)
			return
		case Receiver::CREATE_CALL_CAPABILITY:
			reply_cap (CAPTYPE_RECEIVER | (c->data[0].h ? Receiver::CALL_ASYNC : Receiver::CALL), cap_protected, &((kObject *)cap_protected.l)->refs)
			return
		case Receiver::GET_REPLY_PROTECTED_DATA:
			reply_num (receiver->reply_protected_data.l, receiver->reply_protected_data.h, receiver->protected_only ? 1 : 0)
			return
		case Receiver::SET_REPLY_PROTECTED_DATA:
			receiver->reply_protected_data = c->data[1]
			break
		case Receiver::GET_ALARM:
			reply_num (receiver->alarm_count)
			return
		case Receiver::SET_ALARM:
		case Receiver::ADD_ALARM:
			unsigned old = receiver->alarm_count
			if cmd == Receiver::SET_ALARM:
				receiver->alarm_count = c->data[1].l
			else:
				receiver->alarm_count += c->data[1].l
			if (old == ~0) ^ (receiver->alarm_count == ~0):
				// The alarm stopped or started.
				if old == ~0:
					// It started.
					receiver->prev_alarm = NULL
					receiver->next_alarm = first_alarm
					if receiver->next_alarm:
						receiver->next_alarm->prev_alarm = receiver
					first_alarm = receiver
				else:
					// It stopped.
					if receiver->prev_alarm:
						receiver->prev_alarm->next_alarm = receiver->next_alarm
					else:
						first_alarm = receiver->next_alarm
					if receiver->next_alarm:
						receiver->next_alarm->prev_alarm = receiver->prev_alarm
			reply_num (receiver->alarm_count)
			return
		default:
			reply_num (ERR_INVALID_OPERATION)
			break
	reply_num (0)

static void memory_invoke (unsigned cmd, unsigned target, Num cap_protected, kCapability::Context *c):
	kMemory *mem = (kMemory *)cap_protected.l
	switch cmd:
		case Memory::CREATE:
			switch c->data[0].h:
				case CAPTYPE_RECEIVER:
					kReceiver *ret = mem->alloc_receiver ()
					if ret:
						reply_cap (CAPTYPE_RECEIVER | CAP_MASTER, (unsigned)ret, &ret->refs)
					else:
						reply_num (ERR_OUT_OF_MEMORY)
					return
				case CAPTYPE_MEMORY:
					kMemory *ret = mem->alloc_memory ()
					if ret:
						reply_cap (CAPTYPE_MEMORY | CAP_MASTER, (unsigned)ret, &ret->refs)
					else:
						reply_num (ERR_OUT_OF_MEMORY)
					return
				case CAPTYPE_THREAD:
					kThread *ret = mem->alloc_thread (c->data[1].l)
					if ret:
						reply_cap (CAPTYPE_THREAD | CAP_MASTER, (unsigned)ret, &ret->refs)
					else:
						reply_num (ERR_OUT_OF_MEMORY)
					return
				case CAPTYPE_PAGE:
					kPage *ret = mem->alloc_page ()
					if ret:
						reply_cap (CAPTYPE_PAGE | CAP_MASTER, (unsigned)ret, &ret->refs)
					else:
						reply_num (ERR_OUT_OF_MEMORY)
					return
				case CAPTYPE_CAPS:
					kCaps *ret = mem->alloc_caps (c->data[1].l)
					if ret:
						reply_cap (CAPTYPE_CAPS | CAP_MASTER, (unsigned)ret, &ret->refs)
					else:
						reply_num (ERR_OUT_OF_MEMORY)
					return
				default:
					reply_num (~0)
					return
			break
		case Memory::DESTROY:
			if c->caps->size < 2 || (unsigned)c->caps->cap (1)->target & ~KERNEL_MASK || !c->caps->cap (1)->target || ((kObject *)c->caps->cap (1)->cap_protected.l)->address_space != mem:
				reply_num (~0)
				return
			switch (unsigned)c->caps->cap (1)->target & CAPTYPE_MASK:
				case CAPTYPE_RECEIVER:
					mem->free_receiver ((kReceiver *)c->caps->cap (1)->cap_protected.l)
					break
				case CAPTYPE_MEMORY:
					mem->free_memory ((kMemory *)c->caps->cap (1)->cap_protected.l)
					break
				case CAPTYPE_THREAD:
					mem->free_thread ((kThread *)c->caps->cap (1)->cap_protected.l)
					break
				case CAPTYPE_PAGE:
					mem->free_page ((kPage *)c->caps->cap (1)->cap_protected.l)
					break
				case CAPTYPE_CAPS:
					mem->free_caps ((kCaps *)c->caps->cap (1)->cap_protected.l)
					break
				default:
					panic (0x55228930, "invalid case")
					return
			break
		case Memory::LIST:
			// TODO
			break
		case Memory::MAP:
			// FIXME: this should work for fake pages as well.
			if c->caps->size < 2 || (unsigned)c->caps->cap (1)->target & ~KERNEL_MASK || ((unsigned)c->caps->cap (1)->target & CAPTYPE_MASK) != CAPTYPE_PAGE:
				reply_num (~0)
				return
			kPage *page = (kPage *)c->caps->cap (1)->cap_protected.l
			if page->address_space != mem:
				reply_num (~0)
				return
			bool readonly = c->data[1].l & (unsigned)c->caps->cap (1)->target & Page::READONLY
			mem->map (page, c->data[1].l & PAGE_MASK, readonly)
			break
		case Memory::MAPPING:
			bool readonly
			kPage *page = mem->get_mapping (c->data[1].l, &readonly)
			unsigned t = CAPTYPE_PAGE | CAP_MASTER
			if readonly:
				t |= Page::READONLY
			reply_cap (t, (unsigned)page, &page->refs)
			return
		case Memory::GET_LIMIT:
			reply_num (mem->limit)
			return
		case Memory::SET_LIMIT:
			mem->limit = c->data[1].l
			break
		default:
			reply_num (ERR_INVALID_OPERATION)
			return
	reply_num (0)

static void thread_invoke (unsigned cmd, unsigned target, Num cap_protected, kCapability::Context *c):
	kThread *thread = (kThread *)cap_protected.l
	switch cmd:
		case Thread::GET_INFO:
			switch c->data[0].h:
				case Thread::PC:
					reply_num (thread->pc)
					return
				case Thread::SP:
					reply_num (thread->sp)
					return
				case Thread::FLAGS:
					reply_num (thread->flags)
					return
				default:
					reply_num (*kThread_arch_info (thread, c->data[0].h))
					return
		case Thread::SET_INFO:
			unsigned *value
			switch c->data[1].l:
				case Thread::PC:
					value = &thread->pc
					break
				case Thread::SP:
					value = &thread->sp
					break
				case Thread::FLAGS:
					// It is not possible to set the PRIV flag (but it can be reset).
					if c->data[1].l & Thread::PRIV:
						c->data[1].h &= ~Thread::PRIV
					value = &thread->flags
					if c->data[1].h & ~Thread::USER_FLAGS:
						unsigned v = (*value & ~c->data[1].h) | (c->data[1].l & c->data[1].h)
						if (v & Thread::WAITING) != (*value & Thread::WAITING):
							if v & Thread::WAITING:
								thread->wait ()
							else
								thread->unwait ()
						if (v & Thread::RUNNING) != (*value & Thread::RUNNING):
							if v & Thread::RUNNING:
								thread->run ()
							else
								thread->unrun ()
					break
				default:
					value = kThread_arch_info (thread, c->data[1].l)
					break
			if value:
				*value = (*value & ~c->data[1].h) | (c->data[1].l & c->data[1].h)
			break
		case Thread::SCHEDULE:
			do_schedule = true
			return
	if !(thread->flags & Thread::PRIV):
		reply_num (~0)
		return
	switch cmd:
		case Thread::PRIV_REGISTER_INTERRUPT:
			arch_register_interrupt (c->data[1].l, c->caps->size >= 2 && (((unsigned)c->caps->cap (1)->target) & ~REQUEST_MASK) == CAPTYPE_RECEIVER ? (kReceiver *)c->caps->cap (1)->cap_protected.l : NULL)
			break
		case Thread::PRIV_GET_TOP_MEMORY:
			reply_cap (CAPTYPE_MEMORY | CAP_MASTER, (unsigned)&top_memory, &top_memory.refs)
			return
		case Thread::PRIV_MAKE_PRIV:
			if c->caps->size < 2 || ((unsigned)c->caps->cap (1)->target) & ~REQUEST_MASK != CAPTYPE_THREAD:
				reply_num (~0)
				return
			((kThread *)c->caps->cap (1)->cap_protected.l)->flags |= Thread::PRIV
			break
		case Thread::PRIV_ALLOC_RANGE:
			if c->caps->size < 2 || ((unsigned)c->caps->cap (1)->target) & ~REQUEST_MASK != CAPTYPE_MEMORY:
				reply_num (~0)
				return
			kMemory *mem = (kMemory *)c->caps->cap (1)->cap_protected.l
			if !mem->use (c->data[1].l):
				reply_num (ERR_OUT_OF_MEMORY)
				return
			unsigned data = phys_alloc (c->data[1].l)
			if !data:
				mem->unuse (c->data[1].l)
				reply_num (ERR_OUT_OF_MEMORY)
				return
			reply_num (data & ~0xc0000000)
			return
		case Thread::PRIV_ALLOC_PHYSICAL:
			if c->caps->size < 2 || ((unsigned)c->caps->cap (1)->target) & ~REQUEST_MASK != CAPTYPE_PAGE:
				reply_num (~0)
				return
			kPage *page = (kPage *)c->caps->cap (1)->cap_protected.l
			page->forget ()
			if !(c->data[1].l & 2):
				if page->flags & Page::PAYING:
					page->flags &= ~Page::PAYING
					page->address_space->unuse () 
			else:
				// This is for mapping allocated ranges.  They are already paid for.  Record that.
				if page->flags & Page::PAYING:
					page->address_space->unuse () 
				else:
					page->flags |= Page::PAYING
			page->frame = c->data[1].l & PAGE_MASK
			page->flags |= Page::FRAME
			if !(c->data[1].l & 1):
				page->flags |= Page::UNCACHED
			if !(c->data[1].l & 2):
				page->flags |= Page::PHYSICAL
			kPage_arch_update_mapping (page)
			break
		case Thread::PRIV_PHYSICAL_ADDRESS:
			if c->caps->size < 2 || ((unsigned)c->caps->cap (1)->target) & ~REQUEST_MASK != CAPTYPE_PAGE:
				reply_num (~0)
				return
			kPage *page = (kPage *)c->caps->cap (1)->cap_protected.l
			reply_num (page->frame & ~0xc0000000)
			return
		default:
			reply_num (ERR_INVALID_OPERATION)
			return
	reply_num (0)
	return

static bool page_check_payment (kPage *page):
	kPage *p
	for p = page->share_prev; p; p = p->share_prev:
		if p->flags & Page::PAYING:
			return true
	for p = page->share_next; p; p = p->share_next:
		if p->flags & Page::PAYING:
			return true
	// No kPage is paying for this frame anymore.
	raw_pfree (page->frame)
	kPage *next
	for p = page->share_prev, next = p->share_prev; p; p = next, next = p->share_prev:
		p->frame = NULL
		p->share_prev = NULL
		p->share_next = NULL
		p->flags &= ~(Page::SHARED | Page::FRAME)
		kPage_arch_update_mapping (p)
	for p = page, next = p->share_next; p; p = next, next = p->share_next:
		p->frame = NULL
		p->share_prev = NULL
		p->share_next = NULL
		p->flags &= ~(Page::SHARED | Page::FRAME)
		kPage_arch_update_mapping (p)
	return false

static void page_invoke (unsigned cmd, unsigned target, Num cap_protected, kCapability::Context *c):
	kPage *page = (kPage *)cap_protected.l
	switch cmd & ~Page::READONLY:
		case Page::SHARE:
			if c->caps->size < 2:
				// Cannot share without a target page.
				reply_num (~0)
				return
			if ((unsigned)c->caps->cap (0)->target & ~REQUEST_MASK) != CAPTYPE_PAGE:
				// FIXME: This makes it impossible to use a fake kPage capability.
				break
			kPage *t = (kPage *)c->caps->cap (0)->cap_protected.l
			t->forget ()
			if c->data[0].h & Page::READONLY || cmd & Page::READONLY:
				t->flags |= Page::READONLY
			if !page->flags & Page::FRAME:
				break
			if c->data[0].h & Page::COPY:
				if ~t->flags & Page::PAYING:
					break
				if !(c->data[0].h & Page::FORGET) || page->flags & Page::SHARED:
					unsigned *d = (unsigned *)page->frame
					if t == page:
						kPage *other = page->share_next ? page->share_next : page->share_prev
						if !other:
							kPage_arch_update_mapping (t)
							break
						if page->share_next:
							page->share_next->share_prev = page->share_prev
						if page->share_prev:
							page->share_prev->share_next = page->share_next
						page->share_next = NULL
						page->share_prev = NULL
						page_check_payment (other)
					else:
						t->flags |= Page::FRAME
					t->frame = raw_zalloc ()
					for unsigned i = 0; i <= (c->data[0].h & ~PAGE_MASK); i += 4:
						((unsigned *)t->frame)[i >> 2] = d[i >> 2]
				else:
					if t != page:
						t->frame = page->frame
						t->flags |= Page::FRAME
						page->frame = NULL
						page->flags &= ~Page::FRAME
						kPage_arch_update_mapping (page)
				kPage_arch_update_mapping (t)
			else:
				if t == page:
					break
				if c->data[0].h & Page::FORGET:
					if ~page->flags & Page::SHARED:
						if t->flags & Page::PAYING:
							t->frame = page->frame
							t->flags |= Page::FRAME
						page->frame = NULL
						page->flags &= ~Page::FRAME
						kPage_arch_update_mapping (page)
					else:
						t->share_prev = page->share_prev
						t->share_next = page->share_next
						if t->share_prev:
							t->share_prev->share_next = t
						if t->share_next:
							t->share_next->share_prev = t
						page->share_prev = NULL
						page->share_next = NULL
						page->forget ()
						page_check_payment (t)
				else:
					t->share_prev = page->share_prev
					t->share_next = page
					page->share_prev = t
					if t->share_prev:
						t->share_prev->share_next = t
				kPage_arch_update_mapping (t)
			break
		case Page::SET_FLAGS:
			if cmd & Page::READONLY:
				reply_num (~0)
				return
			// Always refuse to set reserved flags.
			c->data[1].h &= ~(Page::PHYSICAL | Page::UNCACHED)
			// Remember the old flags.
			unsigned old = page->flags
			// Compute the new flags.
			unsigned new_flags = (page->flags & ~c->data[1].h) | (c->data[1].l & c->data[1].h)

			// If we stop paying, see if the frame is still paid for.  If not, free it.
			if ~new_flags & old & Page::PAYING:
				// Decrease the use counter in any case.
				page->address_space->unuse ()
				if !page_check_payment (page):
					new_flags &= ~Page::FRAME

			// If we start paying, increase the use counter.
			if new_flags & ~old & Page::PAYING:
				if !page->address_space->use():
					// If it doesn't work, refuse to set the flag, and refuse to allocate a frame.
					new_flags &= ~(Page::PAYING | Page::FRAME)
					if old & Page::FRAME:
						new_flags |= Page::FRAME

			// If we want a frame, see if we can get it.
			if ~old & new_flags & Page::FRAME:
				kPage *p
				for p = page; p; p = p->share_prev:
					if p->flags & Page::PAYING:
						break
				if !p:
					for p = page->share_next; p; p = p->share_next:
						if p->flags & Page::PAYING:
							break
					if !p:
						new_flags &= ~Page::FRAME
				// If we can get the new frame, get it.
				if ~old & new_flags & Page::FRAME:
					page->frame = page->address_space->zalloc ()
					kPage_arch_update_mapping (page)
			break
		default:
			reply_num (ERR_INVALID_OPERATION)
			break

static void caps_invoke (unsigned cmd, unsigned target, Num cap_protected, kCapability::Context *c):
	kCaps *caps = (kCapsP)cap_protected.l
	switch cmd:
		default:
			reply_num (ERR_INVALID_OPERATION)
			break

static void kill_reply (kCapability *self):
	while self->parent:
		self = self->parent.deref ()
	while self->sibling_prev:
		self->sibling_prev->invalidate ()
	while self->sibling_next:
		self->sibling_next->invalidate ()
	self->invalidate ()

static void kernel_invoke (unsigned target, Num cap_protected, kCapability::Context *c, kCapability *self):
	// Kernel calling convention:
	// data[0].l is the request.
	// caps[0] is the reply capability
	// other parameters' meanings depend on the operation.
	if target == (CAPTYPE_RECEIVER | Receiver::CALL) || target == (CAPTYPE_RECEIVER | Receiver::CALL_ASYNC):
		// This is a call capability.  caps->cap (0) is the capability to call.  It should be replaced by the reply capability.
		if !c->caps || c->caps->size == 0:
			// No caps, so no target to call.
			return
		reply_target = (kReceiver *)cap_protected.l
		reply_target->protected_only = target == (CAPTYPE_RECEIVER | Receiver::CALL)
		kReceiver *call_target = c->caps->cap (0)->target
		Num call_cap_protected = c->caps->cap (0)->cap_protected
		if ((unsigned)call_target & ~KERNEL_MASK) != 0:
			// This is a user-implemented object.  Create a real reply capability.
			c->caps->cap (0)->invalidate ()
			c->caps->set (0, (kReceiver *)(CAPTYPE_RECEIVER | Receiver::REPLY), cap_protected, kCapRef (), &((kReceiver *)cap_protected.l)->refs)
			call_target->send_message (call_cap_protected, c)
		else if (unsigned)call_target == CAPTYPE_RECEIVER | Receiver::REPLY:
			// Reply capability: destroy all before invoke.
			kill_reply (c->caps->cap (0))
			kReceiver *r = (kReceiver *)call_cap_protected.l
			r->send_message (r->reply_protected_data, c)
		else:
			// Kernel call: don't create actual capablities.
			reply_protected = reply_target->reply_protected_data
			c->caps->cap (0)->invalidate ()
			kernel_invoke ((unsigned)call_target, call_cap_protected, c, NULL)
		return
	if target == CAPTYPE_RECEIVER | Receiver::REPLY:
		// This is a reply capability.
		kReceiver *r = (kReceiver *)cap_protected.l
		kill_reply (self)
		r->send_message (r->reply_protected_data, c)
		return
	reply = kCapRef (c->caps, 0)
	unsigned cmd
	if (target & REQUEST_MASK) == CAP_MASTER:
		if c->data[0].l & CAP_MASTER_CREATE:
			reply_cap (target | (c->data[0].l & REQUEST_MASK), cap_protected, &((kObject *)cap_protected.l)->refs)
			return
		cmd = c->data[0].l
		c->data[0].l = 0
	else:
		cmd = target & REQUEST_MASK
	switch target & CAPTYPE_MASK:
		case CAPTYPE_RECEIVER:
			receiver_invoke (cmd, target, cap_protected, c)
			break
		case CAPTYPE_MEMORY:
			memory_invoke (cmd, target, cap_protected, c)
			break
		case CAPTYPE_THREAD:
			thread_invoke (cmd, target, cap_protected, c)
			break
		case CAPTYPE_PAGE:
			page_invoke (cmd, target, cap_protected, c)
			break
		case CAPTYPE_CAPS:
			caps_invoke (cmd, target, cap_protected, c)
			break
		default:
			panic (0x99337744, "invalid capability type invoked")
			return
	return

void invoke (kReceiverP target, Num cap_protected, kCapability::Context *c, kCapability *self):
	if (unsigned)target & ~KERNEL_MASK:
		// This is not a kernel capability: send a message to the receiver.
		target->send_message (cap_protected, c)
		return
	// This is a kernel capability.  Use a function to allow optimized call capabilities.
	if !c->caps || c->caps->size < 1:
		reply_target = NULL
	else:
		reply_target = c->caps->cap (1)->target
		reply_protected = c->caps->cap (1)->cap_protected
	kernel_invoke ((unsigned)target, cap_protected, c, self)