Initial sketch for the generic data-transfer interface.

src/core/interface.c

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+/*
+ * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * 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 2 of the
+ * License, or 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, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <assert.h>
+#include <gpxe/interface.h>
+
+/** @file
+ *
+ * Object communication interfaces
+ *
+ */
+
+/**
+ * Obtain reference to interface
+ *
+ * @v intf		Interface
+ * @ret intf		Interface
+ *
+ * Increases the reference count on the interface.
+ */
+static struct interface * intf_get ( struct interface *intf ) {
+	intf->refcnt ( intf, +1 );
+	return intf;
+}
+
+/**
+ * Drop reference to interface
+ *
+ * @v intf		Interface
+ *
+ * Decreases the reference count on the interface.
+ */
+static void intf_put ( struct interface *intf ) {
+	intf->refcnt ( intf, -1 );
+}
+
+/**
+ * Plug an interface into a new destination interface
+ *
+ * @v intf		Interface
+ * @v dest		New destination interface
+ *
+ * The reference to the existing destination interface is dropped, a
+ * reference to the new destination interface is obtained, and the
+ * interface is updated to point to the new destination interface.
+ *
+ * Note that there is no "unplug" call; instead you must plug the
+ * interface into a null interface.
+ */
+void plug ( struct interface *intf, struct interface *dest ) {
+	intf_put ( intf->dest );
+	intf->dest = intf_get ( dest );
+}
+
+/**
+ * Null update reference count
+ *
+ * @v intf		Interface
+ * @v delta		Change to apply to reference count
+ *
+ * Use this as the refcnt() method for an interface that does not need
+ * to support reference counting.
+ */
+void null_refcnt ( struct interface *intf __unused, int delta __unused ) {
+	/* Do nothing */
+}

src/core/xfer.c

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+/*
+ * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * 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 2 of the
+ * License, or 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, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <errno.h>
+#include <gpxe/xfer.h>
+
+/** @file
+ *
+ * Data transfer interfaces
+ *
+ */
+
+/**
+ * Deliver datagram
+ *
+ * @v xfer		Data-transfer interface
+ * @v iobuf		Datagram I/O buffer
+ * @ret rc		Return status code
+ */
+int deliver ( struct xfer_interface *xfer, struct io_buffer *iobuf ) {
+	struct xfer_interface *dest = xfer_dest ( xfer );
+
+	return dest->op->deliver ( dest, xfer, iobuf );
+}
+
+/**
+ * Null deliver datagram
+ *
+ * @v xfer		Data-transfer interface
+ * @v src		Source interface
+ * @v iobuf		Datagram I/O buffer
+ * @ret rc		Return status code
+ */
+static int null_deliver ( struct xfer_interface *xfer __unused,
+			  struct xfer_interface *src __unused,
+			  struct io_buffer *iobuf ) {
+	free_iob ( iobuf );
+	return -EPIPE;
+}
+
+/** Null data transfer interface operations */
+struct xfer_interface_operations null_xfer_ops = {
+	.deliver = null_deliver,
+};
+
+/**
+ * Null data transfer interface
+ *
+ * This is the interface to which data transfer interfaces are
+ * connected when unplugged.  It will never generate messages, and
+ * will silently absorb all received messages.
+ */
+struct xfer_interface null_xfer = {
+	.intf = {
+		.dest = &null_xfer.intf,
+		.refcnt = null_refcnt,
+	},
+	.op = &null_xfer_ops,
+};