xpc_channel.c

linux 内核源代码

			"channel=%d\n", put, ch->partid, ch->number);

		send_IPI = 1;

		/*
		 * We need to ensure that the message referenced by
		 * local_GP->put is not XPC_M_READY or that local_GP->put
		 * equals w_local_GP.put, so we'll go have a look.
		 */
		initial_put = put;
	}

	if (send_IPI) {
		xpc_IPI_send_msgrequest(ch);
	}
}


/*
 * Common code that does the actual sending of the message by advancing the
 * local message queue's Put value and sends an IPI to the partition the
 * message is being sent to.
 */
static enum xpc_retval
xpc_send_msg(struct xpc_channel *ch, struct xpc_msg *msg, u8 notify_type,
			xpc_notify_func func, void *key)
{
	enum xpc_retval ret = xpcSuccess;
	struct xpc_notify *notify = notify;
	s64 put, msg_number = msg->number;


	DBUG_ON(notify_type == XPC_N_CALL && func == NULL);
	DBUG_ON((((u64) msg - (u64) ch->local_msgqueue) / ch->msg_size) !=
					msg_number % ch->local_nentries);
	DBUG_ON(msg->flags & XPC_M_READY);

	if (ch->flags & XPC_C_DISCONNECTING) {
		/* drop the reference grabbed in xpc_allocate_msg() */
		xpc_msgqueue_deref(ch);
		return ch->reason;
	}

	if (notify_type != 0) {
		/*
		 * Tell the remote side to send an ACK interrupt when the
		 * message has been delivered.
		 */
		msg->flags |= XPC_M_INTERRUPT;

		atomic_inc(&ch->n_to_notify);

		notify = &ch->notify_queue[msg_number % ch->local_nentries];
		notify->func = func;
		notify->key = key;
		notify->type = notify_type;

		// >>> is a mb() needed here?

		if (ch->flags & XPC_C_DISCONNECTING) {
			/*
			 * An error occurred between our last error check and
			 * this one. We will try to clear the type field from
			 * the notify entry. If we succeed then
			 * xpc_disconnect_channel() didn't already process
			 * the notify entry.
			 */
			if (cmpxchg(&notify->type, notify_type, 0) ==
								notify_type) {
				atomic_dec(&ch->n_to_notify);
				ret = ch->reason;
			}

			/* drop the reference grabbed in xpc_allocate_msg() */
			xpc_msgqueue_deref(ch);
			return ret;
		}
	}

	msg->flags |= XPC_M_READY;

	/*
	 * The preceding store of msg->flags must occur before the following
	 * load of ch->local_GP->put.
	 */
	mb();

	/* see if the message is next in line to be sent, if so send it */

	put = ch->local_GP->put;
	if (put == msg_number) {
		xpc_send_msgs(ch, put);
	}

	/* drop the reference grabbed in xpc_allocate_msg() */
	xpc_msgqueue_deref(ch);
	return ret;
}


/*
 * Send a message previously allocated using xpc_initiate_allocate() on the
 * specified channel connected to the specified partition.
 *
 * This routine will not wait for the message to be received, nor will
 * notification be given when it does happen. Once this routine has returned
 * the message entry allocated via xpc_initiate_allocate() is no longer
 * accessable to the caller.
 *
 * This routine, although called by users, does not call xpc_part_ref() to
 * ensure that the partition infrastructure is in place. It relies on the
 * fact that we called xpc_msgqueue_ref() in xpc_allocate_msg().
 *
 * Arguments:
 *
 *	partid - ID of partition to which the channel is connected.
 *	ch_number - channel # to send message on.
 *	payload - pointer to the payload area allocated via
 *			xpc_initiate_allocate().
 */
enum xpc_retval
xpc_initiate_send(partid_t partid, int ch_number, void *payload)
{
	struct xpc_partition *part = &xpc_partitions[partid];
	struct xpc_msg *msg = XPC_MSG_ADDRESS(payload);
	enum xpc_retval ret;


	dev_dbg(xpc_chan, "msg=0x%p, partid=%d, channel=%d\n", (void *) msg,
		partid, ch_number);

	DBUG_ON(partid <= 0 || partid >= XP_MAX_PARTITIONS);
	DBUG_ON(ch_number < 0 || ch_number >= part->nchannels);
	DBUG_ON(msg == NULL);

	ret = xpc_send_msg(&part->channels[ch_number], msg, 0, NULL, NULL);

	return ret;
}


/*
 * Send a message previously allocated using xpc_initiate_allocate on the
 * specified channel connected to the specified partition.
 *
 * This routine will not wait for the message to be sent. Once this routine
 * has returned the message entry allocated via xpc_initiate_allocate() is no
 * longer accessable to the caller.
 *
 * Once the remote end of the channel has received the message, the function
 * passed as an argument to xpc_initiate_send_notify() will be called. This
 * allows the sender to free up or re-use any buffers referenced by the
 * message, but does NOT mean the message has been processed at the remote
 * end by a receiver.
 *
 * If this routine returns an error, the caller's function will NOT be called.
 *
 * This routine, although called by users, does not call xpc_part_ref() to
 * ensure that the partition infrastructure is in place. It relies on the
 * fact that we called xpc_msgqueue_ref() in xpc_allocate_msg().
 *
 * Arguments:
 *
 *	partid - ID of partition to which the channel is connected.
 *	ch_number - channel # to send message on.
 *	payload - pointer to the payload area allocated via
 *			xpc_initiate_allocate().
 *	func - function to call with asynchronous notification of message
 *		  receipt. THIS FUNCTION MUST BE NON-BLOCKING.
 *	key - user-defined key to be passed to the function when it's called.
 */
enum xpc_retval
xpc_initiate_send_notify(partid_t partid, int ch_number, void *payload,
				xpc_notify_func func, void *key)
{
	struct xpc_partition *part = &xpc_partitions[partid];
	struct xpc_msg *msg = XPC_MSG_ADDRESS(payload);
	enum xpc_retval ret;


	dev_dbg(xpc_chan, "msg=0x%p, partid=%d, channel=%d\n", (void *) msg,
		partid, ch_number);

	DBUG_ON(partid <= 0 || partid >= XP_MAX_PARTITIONS);
	DBUG_ON(ch_number < 0 || ch_number >= part->nchannels);
	DBUG_ON(msg == NULL);
	DBUG_ON(func == NULL);

	ret = xpc_send_msg(&part->channels[ch_number], msg, XPC_N_CALL,
								func, key);
	return ret;
}


static struct xpc_msg *
xpc_pull_remote_msg(struct xpc_channel *ch, s64 get)
{
	struct xpc_partition *part = &xpc_partitions[ch->partid];
	struct xpc_msg *remote_msg, *msg;
	u32 msg_index, nmsgs;
	u64 msg_offset;
	enum xpc_retval ret;


	if (mutex_lock_interruptible(&ch->msg_to_pull_mutex) != 0) {
		/* we were interrupted by a signal */
		return NULL;
	}

	while (get >= ch->next_msg_to_pull) {

		/* pull as many messages as are ready and able to be pulled */

		msg_index = ch->next_msg_to_pull % ch->remote_nentries;

		DBUG_ON(ch->next_msg_to_pull >=
					(volatile s64) ch->w_remote_GP.put);
		nmsgs =  (volatile s64) ch->w_remote_GP.put -
						ch->next_msg_to_pull;
		if (msg_index + nmsgs > ch->remote_nentries) {
			/* ignore the ones that wrap the msg queue for now */
			nmsgs = ch->remote_nentries - msg_index;
		}

		msg_offset = msg_index * ch->msg_size;
		msg = (struct xpc_msg *) ((u64) ch->remote_msgqueue +
								msg_offset);
		remote_msg = (struct xpc_msg *) (ch->remote_msgqueue_pa +
								msg_offset);

		if ((ret = xpc_pull_remote_cachelines(part, msg, remote_msg,
				nmsgs * ch->msg_size)) != xpcSuccess) {

			dev_dbg(xpc_chan, "failed to pull %d msgs starting with"
				" msg %ld from partition %d, channel=%d, "
				"ret=%d\n", nmsgs, ch->next_msg_to_pull,
				ch->partid, ch->number, ret);

			XPC_DEACTIVATE_PARTITION(part, ret);

			mutex_unlock(&ch->msg_to_pull_mutex);
			return NULL;
		}

		mb();	/* >>> this may not be needed, we're not sure */

		ch->next_msg_to_pull += nmsgs;
	}

	mutex_unlock(&ch->msg_to_pull_mutex);

	/* return the message we were looking for */
	msg_offset = (get % ch->remote_nentries) * ch->msg_size;
	msg = (struct xpc_msg *) ((u64) ch->remote_msgqueue + msg_offset);

	return msg;
}


/*
 * Get a message to be delivered.
 */
static struct xpc_msg *
xpc_get_deliverable_msg(struct xpc_channel *ch)
{
	struct xpc_msg *msg = NULL;
	s64 get;


	do {
		if ((volatile u32) ch->flags & XPC_C_DISCONNECTING) {
			break;
		}

		get = (volatile s64) ch->w_local_GP.get;
		if (get == (volatile s64) ch->w_remote_GP.put) {
			break;
		}

		/* There are messages waiting to be pulled and delivered.
		 * We need to try to secure one for ourselves. We'll do this
		 * by trying to increment w_local_GP.get and hope that no one
		 * else beats us to it. If they do, we'll we'll simply have
		 * to try again for the next one.
	 	 */

		if (cmpxchg(&ch->w_local_GP.get, get, get + 1) == get) {
			/* we got the entry referenced by get */

			dev_dbg(xpc_chan, "w_local_GP.get changed to %ld, "
				"partid=%d, channel=%d\n", get + 1,
				ch->partid, ch->number);

			/* pull the message from the remote partition */

			msg = xpc_pull_remote_msg(ch, get);

			DBUG_ON(msg != NULL && msg->number != get);
			DBUG_ON(msg != NULL && (msg->flags & XPC_M_DONE));
			DBUG_ON(msg != NULL && !(msg->flags & XPC_M_READY));

			break;
		}

	} while (1);

	return msg;
}


/*
 * Deliver a message to its intended recipient.
 */
void
xpc_deliver_msg(struct xpc_channel *ch)
{
	struct xpc_msg *msg;


	if ((msg = xpc_get_deliverable_msg(ch)) != NULL) {

		/*
		 * This ref is taken to protect the payload itself from being
		 * freed before the user is finished with it, which the user
		 * indicates by calling xpc_initiate_received().
		 */
		xpc_msgqueue_ref(ch);

		atomic_inc(&ch->kthreads_active);

		if (ch->func != NULL) {
			dev_dbg(xpc_chan, "ch->func() called, msg=0x%p, "
				"msg_number=%ld, partid=%d, channel=%d\n",
				(void *) msg, msg->number, ch->partid,
				ch->number);

			/* deliver the message to its intended recipient */
			ch->func(xpcMsgReceived, ch->partid, ch->number,
					&msg->payload, ch->key);

			dev_dbg(xpc_chan, "ch->func() returned, msg=0x%p, "
				"msg_number=%ld, partid=%d, channel=%d\n",
				(void *) msg, msg->number, ch->partid,
				ch->number);
		}

		atomic_dec(&ch->kthreads_active);
	}
}


/*
 * Now we actually acknowledge the messages that have been delivered and ack'd
 * by advancing the cached remote message queue's Get value and if requested
 * send an IPI to the message sender's partition.
 */
static void
xpc_acknowledge_msgs(struct xpc_channel *ch, s64 initial_get, u8 msg_flags)
{
	struct xpc_msg *msg;
	s64 get = initial_get + 1;
	int send_IPI = 0;


	while (1) {

		while (1) {
			if (get == (volatile s64) ch->w_local_GP.get) {
				break;
			}

			msg = (struct xpc_msg *) ((u64) ch->remote_msgqueue +
			       (get % ch->remote_nentries) * ch->msg_size);

			if (!(msg->flags & XPC_M_DONE)) {
				break;
			}

			msg_flags |= msg->flags;
			get++;
		}

		if (get == initial_get) {
			/* nothing's changed */
			break;
		}

		if (cmpxchg_rel(&ch->local_GP->get, initial_get, get) !=
								initial_get) {
			/* someone else beat us to it */
			DBUG_ON((volatile s64) ch->local_GP->get <=
								initial_get);
			break;
		}

		/* we just set the new value of local_GP->get */

		dev_dbg(xpc_chan, "local_GP->get changed to %ld, partid=%d, "
			"channel=%d\n", get, ch->partid, ch->number);

		send_IPI = (msg_flags & XPC_M_INTERRUPT);

		/*
		 * We need to ensure that the message referenced by
		 * local_GP->get is not XPC_M_DONE or that local_GP->get
		 * equals w_local_GP.get, so we'll go have a look.
		 */
		initial_get = get;
	}

	if (send_IPI) {
		xpc_IPI_send_msgrequest(ch);
	}
}


/*
 * Acknowledge receipt of a delivered message.
 *
 * If a message has XPC_M_INTERRUPT set, send an interrupt to the partition
 * that sent the message.
 *
 * This function, although called by users, does not call xpc_part_ref() to
 * ensure that the partition infrastructure is in place. It relies on the
 * fact that we called xpc_msgqueue_ref() in xpc_deliver_msg().
 *
 * Arguments:
 *
 *	partid - ID of partition to which the channel is connected.
 *	ch_number - channel # message received on.
 *	payload - pointer to the payload area allocated via
 *			xpc_initiate_allocate().
 */
void
xpc_initiate_received(partid_t partid, int ch_number, void *payload)
{
	struct xpc_partition *part = &xpc_partitions[partid];
	struct xpc_channel *ch;
	struct xpc_msg *msg = XPC_MSG_ADDRESS(payload);
	s64 get, msg_number = msg->number;


	DBUG_ON(partid <= 0 || partid >= XP_MAX_PARTITIONS);
	DBUG_ON(ch_number < 0 || ch_number >= part->nchannels);

	ch = &part->channels[ch_number];

	dev_dbg(xpc_chan, "msg=0x%p, msg_number=%ld, partid=%d, channel=%d\n",
		(void *) msg, msg_number, ch->partid, ch->number);

	DBUG_ON((((u64) msg - (u64) ch->remote_msgqueue) / ch->msg_size) !=
					msg_number % ch->remote_nentries);
	DBUG_ON(msg->flags & XPC_M_DONE);

	msg->flags |= XPC_M_DONE;

	/*
	 * The preceding store of msg->flags must occur before the following
	 * load of ch->local_GP->get.
	 */
	mb();

	/*
	 * See if this message is next in line to be acknowledged as having
	 * been delivered.
	 */
	get = ch->local_GP->get;
	if (get == msg_number) {
		xpc_acknowledge_msgs(ch, get, msg->flags);
	}

	/* the call to xpc_msgqueue_ref() was done by xpc_deliver_msg()  */
	xpc_msgqueue_deref(ch);
}