First chunks:
From 92df068dc5acae9e671eefe1f80626319819c52b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ji=C5=99=C3=AD=20Pinkava?= <j-pi@seznam.cz>
Date: Tue, 17 Mar 2015 13:21:09 +0100
Subject: [PATCH] New functions rtlsdr_set_tuner_bandwidth()

Index: src/librtlsdr.c
--- src/librtlsdr.c.orig
+++ src/librtlsdr.c
@@ -85,6 +85,7 @@ struct rtlsdr_dev {
 	rtlsdr_tuner_iface_t *tuner;
 	uint32_t tun_xtal; /* Hz */
 	uint32_t freq; /* Hz */
+	uint32_t bw;
 	uint32_t offs_freq; /* Hz */
 	int corr; /* ppm */
 	int gain; /* tenth dB */
@@ -906,6 +907,24 @@ int rtlsdr_get_tuner_gains(rtlsdr_dev_t *dev, int *gai
 	}
 }
 
+int rtlsdr_set_tuner_bandwidth(rtlsdr_dev_t *dev, uint32_t bw)
+{
+	int r = 0;
+
+	if (!dev || !dev->tuner)
+		return -1;
+
+	if (dev->tuner->set_bw) {
+		rtlsdr_set_i2c_repeater(dev, 1);
+		r = dev->tuner->set_bw(dev, bw > 0 ? bw : dev->rate);
+		rtlsdr_set_i2c_repeater(dev, 0);
+		if (r)
+			return r;
+		dev->bw = bw;
+	}
+	return r;
+}
+
 int rtlsdr_set_tuner_gain(rtlsdr_dev_t *dev, int gain)
 {
 	int r = 0;
@@ -989,14 +1008,14 @@ int rtlsdr_set_sample_rate(rtlsdr_dev_t *dev, uint32_t
 	if ( ((double)samp_rate) != real_rate )
 		fprintf(stderr, "Exact sample rate is: %f Hz\n", real_rate);
 
+	dev->rate = (uint32_t)real_rate;
+
 	if (dev->tuner && dev->tuner->set_bw) {
 		rtlsdr_set_i2c_repeater(dev, 1);
-		dev->tuner->set_bw(dev, (int)real_rate);
+		dev->tuner->set_bw(dev, dev->bw > 0 ? dev->bw : dev->rate);
 		rtlsdr_set_i2c_repeater(dev, 0);
 	}
 
-	dev->rate = (uint32_t)real_rate;
-
 	tmp = (rsamp_ratio >> 16);
 	r |= rtlsdr_demod_write_reg(dev, 1, 0x9f, tmp, 2);
 	tmp = rsamp_ratio & 0xffff;
@@ -1112,6 +1131,7 @@ int rtlsdr_get_direct_sampling(rtlsdr_dev_t *dev)
 int rtlsdr_set_offset_tuning(rtlsdr_dev_t *dev, int on)
 {
 	int r = 0;
+	int bw;
 
 	if (!dev)
 		return -1;
@@ -1128,7 +1148,14 @@ int rtlsdr_set_offset_tuning(rtlsdr_dev_t *dev, int on
 
 	if (dev->tuner && dev->tuner->set_bw) {
 		rtlsdr_set_i2c_repeater(dev, 1);
-		dev->tuner->set_bw(dev, on ? (2 * dev->offs_freq) : dev->rate);
+		if (on) {
+			bw = 2 * dev->offs_freq;
+		} else if (dev->bw > 0) {
+			bw = dev->bw;
+		} else {
+			bw = dev->rate;
+		}
+		dev->tuner->set_bw(dev, bw);
 		rtlsdr_set_i2c_repeater(dev, 0);
 	}
 
@@ -1340,10 +1367,12 @@ int rtlsdr_open(rtlsdr_dev_t **out_dev, uint32_t index
 	r = libusb_open(device, &dev->devh);
 	if (r < 0) {
 		libusb_free_device_list(list, 1);
-		fprintf(stderr, "usb_open error %d\n", r);
+		fprintf(stderr, "libusb_open error %s (%d)\n", libusb_error_name(r), r);
 		if(r == LIBUSB_ERROR_ACCESS)
-			fprintf(stderr, "Please fix the device permissions, e.g. "
-			"by installing the udev rules file rtl-sdr.rules\n");
+			fprintf(stderr, "No permission to access the relevant /dev/ugen devices.\n");
+		else if(r == LIBUSB_ERROR_NO_DEVICE)
+			fprintf(stderr, "Check that you have sufficient /dev/ugen nodes for your device.\n"
+			    "You may need to run sh MAKEDEV ugen[number].\n");
 		goto err;
 	}