Bug #411 #651 - don't create tap0 if it already exists

docs/CHANGELOG

@@ -19,6 +19,7 @@
     - fix configure --without-libdnet (#567)
     - ensure automake version is at least 1.15 (#553)
     - with multiplier option only first file can be sent and hang (#472)
+    - do not create tap0 if device already exists (#411) (#651)
 
 05/20/2020 Version 4.3.3
     - Increase cache buffers size to accomodate VLAN edits (#594)

src/common/sendpacket.c

@@ -473,13 +473,23 @@ sendpacket_t *
 sendpacket_open(const char *device, char *errbuf, tcpr_dir_t direction,
         sendpacket_type_t sendpacket_type _U_, void *arg _U_)
 {
+#ifdef HAVE_TUNTAP
+    char sys_dev_dir[128];
+    bool device_exists;
+#endif
     sendpacket_t *sp;
     struct stat sdata;
 
     assert(device);
     assert(errbuf);
 
     errbuf[0] = '\0';
+
+#ifdef HAVE_TUNTAP
+    snprintf(sys_dev_dir, sizeof(sys_dev_dir), "/sys/class/net/%s/", device);
+    device_exists = access(sys_dev_dir, R_OK) == 0;
+#endif
+
     /* khial is universal */
     if (stat(device, &sdata) == 0) {
         if (((sdata.st_mode & S_IFMT) == S_IFCHR)) { 
@@ -515,7 +525,7 @@ sendpacket_open(const char *device, char *errbuf, tcpr_dir_t direction,
               }
         }
 #ifdef HAVE_TUNTAP
-    } else if (strncmp(device, "tap", 3) == 0) {
+    } else if (strncmp(device, "tap", 3) == 0 && !device_exists) {
         sp = sendpacket_open_tuntap(device, errbuf);
 #endif
     } else {