lib: don't detach kernel driver by default

Since this feature also disconnects running instances
of librtlsdr that claimed the device, it is now disabled
by default and can only be enabled at compile time.

To enable it when building with cmake:
cmake . -DDETACH_KERNEL_DRIVER=ON

To enable it when building with automake:
./configure --enable-driver-detach

Signed-off-by: Steve Markgraf <steve@steve-m.de>

CMakeLists.txt

@@ -111,6 +111,14 @@ else (INSTALL_UDEV_RULES)
     message (STATUS "Udev rules not being installed, install them with -DINSTALL_UDEV_RULES=ON")
 endif (INSTALL_UDEV_RULES)
 
+option(DETACH_KERNEL_DRIVER "Detach kernel driver if loaded" OFF)
+if (DETACH_KERNEL_DRIVER)
+    message (STATUS "Building with kernel driver detaching enabled")
+    add_definitions(-DDETACH_KERNEL_DRIVER=1)
+else (DETACH_KERNEL_DRIVER)
+    message (STATUS "Building with kernel driver detaching disabled, use -DDETACH_KERNEL_DRIVER=ON to enable")
+endif (DETACH_KERNEL_DRIVER)
+
 ########################################################################
 # Add subdirectories
 ########################################################################

configure.ac

@@ -64,6 +64,12 @@ AC_TRY_COMPILE([],[],
   AC_MSG_RESULT(no)
   CFLAGS="$old_CFLAGS")
 
+AC_ARG_ENABLE(driver-detach,
+[  --enable-driver-detach          Enable detaching of kernel driver (disabled by default)],
+[if test x$enableval = xyes; then
+    CFLAGS="$CFLAGS -DDETACH_KERNEL_DRIVER"
+fi])
+
 dnl Generate the output
 AC_CONFIG_HEADER(config.h)
 

src/librtlsdr.c

@@ -1351,12 +1351,22 @@ int rtlsdr_open(rtlsdr_dev_t **out_dev, uint32_t index)
 
 	if (libusb_kernel_driver_active(dev->devh, 0) == 1) {
 		dev->driver_active = 1;
+
+#ifdef DETACH_KERNEL_DRIVER
 		if (!libusb_detach_kernel_driver(dev->devh, 0)) {
 			fprintf(stderr, "Detached kernel driver\n");
 		} else {
 			fprintf(stderr, "Detaching kernel driver failed!");
 			goto err;
 		}
+#else
+		fprintf(stderr, "\nKernel driver is active, or device is "
+				"claimed by second instance of librtlsdr."
+				"\nIn the first case, please either detach"
+				" or blacklist the kernel module\n"
+				"(dvb_usb_rtl28xxu), or enable automatic"
+				" detaching at compile time.\n\n");
+#endif
 	}
 
 	r = libusb_claim_interface(dev->devh, 0);
@@ -1484,12 +1494,14 @@ int rtlsdr_close(rtlsdr_dev_t *dev)
 
 	libusb_release_interface(dev->devh, 0);
 
+#ifdef DETACH_KERNEL_DRIVER
 	if (dev->driver_active) {
 		if (!libusb_attach_kernel_driver(dev->devh, 0))
 			fprintf(stderr, "Reattached kernel driver\n");
 		else
 			fprintf(stderr, "Reattaching kernel driver failed!\n");
 	}
+#endif
 
 	libusb_close(dev->devh);