transform: Add a "nop" transform module.

This doesn't do anything, just passes input packets on unmodified.

Makefile.am

@@ -70,7 +70,8 @@ libsigrok_la_SOURCES += \
 
 # Transform modules
 libsigrok_la_SOURCES += \
-	src/transform/transform.c
+	src/transform/transform.c \
+	src/transform/nop.c
 
 # SCPI support
 libsigrok_la_SOURCES += \

src/transform/nop.c

@@ -0,0 +1,49 @@
+/*
+ * This file is part of the libsigrok project.
+ *
+ * Copyright (C) 2015 Uwe Hermann <uwe@hermann-uwe.de>
+ *
+ * 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
+ * (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, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+ */
+
+#include <string.h>
+#include "libsigrok.h"
+#include "libsigrok-internal.h"
+
+#define LOG_PREFIX "transform/nop"
+
+static int receive(const struct sr_transform *t,
+		struct sr_datafeed_packet *packet_in,
+		struct sr_datafeed_packet **packet_out)
+{
+	if (!t || !t->sdi || !packet_in || !packet_out)
+		return SR_ERR_ARG;
+
+	/* Do nothing, just pass on packets unmodified. */
+	sr_spew("Received packet of type %d, passing on unmodified.", packet_in->type);
+	*packet_out = packet_in;
+
+	return SR_OK;
+}
+
+SR_PRIV struct sr_transform_module transform_nop = {
+	.id = "nop",
+	.name = "NOP",
+	.desc = "Do nothing",
+	.options = NULL,
+	.init = NULL,
+	.receive = receive,
+	.cleanup = NULL,
+};

src/transform/transform.c

@@ -39,9 +39,11 @@
  */
 
 /** @cond PRIVATE */
+extern SR_PRIV struct sr_transform_module transform_nop;
 /* @endcond */
 
 static const struct sr_transform_module *transform_module_list[] = {
+	&transform_nop,
 	NULL,
 };