Replace usb_set_debug() in utils by new group in LIBNFC_LOG_LEVEL

To use it: (NFC_LOG_PRIORITY_DEBUG * 2 ^ NFC_LOG_GROUP_LIBUSB)
LIBUSB_LOG_LEVEL=12288

libnfc/buses/usbbus.c

@@ -38,6 +38,16 @@ int usb_prepare(void)
   if (usb_initialized) {
     return 0;
   }
+
+#ifdef ENVVARS
+  char *env_log_level = getenv("LIBNFC_LOG_LEVEL");
+  // Set libusb debug only if asked explicitely:
+  // LIBUSB_LOG_LEVEL=12288 (= NFC_LOG_PRIORITY_DEBUG * 2 ^ NFC_LOG_GROUP_LIBUSB)
+  if (env_log_level && (((atoi(env_log_level) >> (NFC_LOG_GROUP_LIBUSB * 2)) & 0x00000003) >= NFC_LOG_PRIORITY_DEBUG)) {
+    setenv("USB_DEBUG", "255", 1);
+  }
+#endif
+
   usb_init();
   usb_initialized = true;
 

libnfc/log.h

@@ -35,6 +35,7 @@
 #define NFC_LOG_GROUP_CHIP      3
 #define NFC_LOG_GROUP_DRIVER    4
 #define NFC_LOG_GROUP_COM       5
+#define NFC_LOG_GROUP_LIBUSB    6
 
 /*
   To enable log only for one (or more) group, you can use this formula:

utils/nfc-list.c

@@ -38,12 +38,6 @@
 #  include "config.h"
 #endif // HAVE_CONFIG_H
 
-#ifdef HAVE_LIBUSB
-#  ifdef DEBUG
-#    include <usb.h>
-#  endif
-#endif
-
 #include <err.h>
 #include <stdio.h>
 #include <stddef.h>
@@ -90,12 +84,6 @@ main(int argc, const char *argv[])
     }
   }
 
-#ifdef HAVE_LIBUSB
-#  ifdef DEBUG
-  usb_set_debug(4);
-#  endif
-#endif
-
   /* Lazy way to open an NFC device */
 #if 0
   pnd = nfc_open(context, NULL);

utils/nfc-scan-device.c

@@ -38,12 +38,6 @@
 #  include "config.h"
 #endif // HAVE_CONFIG_H
 
-#ifdef HAVE_LIBUSB
-#  ifdef DEBUG
-#    include <usb.h>
-#  endif
-#endif
-
 #include <err.h>
 #include <stdio.h>
 #include <stddef.h>
@@ -101,12 +95,6 @@ main(int argc, const char *argv[])
   acLibnfcVersion = nfc_version();
   printf("%s uses libnfc %s\n", argv[0], acLibnfcVersion);
 
-#ifdef HAVE_LIBUSB
-#  ifdef DEBUG
-  usb_set_debug(4);
-#  endif
-#endif
-
   nfc_connstring connstrings[MAX_DEVICE_COUNT];
   size_t szDeviceFound = nfc_list_devices(context, connstrings, MAX_DEVICE_COUNT);