Add support for external network.

Dynamically load external network from libnccl-net.so.
Add init function in networks.
Move PCI scoring to net.cu, only ask transport to provide a path.
Simplify CUDA PCI path detection.
Add dummy external network

src/include/socket.h

@@ -76,7 +76,7 @@ static int findInterfaces(const char* prefixList, char* names, union socketAddre
     if (family != AF_INET && family != AF_INET6)
       continue;
 
-    TRACE(INIT|NET,"Found interface %s:%s", interface->ifa_name, socketToString(interface->ifa_addr, line));
+    TRACE(NCCL_INIT|NCCL_NET,"Found interface %s:%s", interface->ifa_name, socketToString(interface->ifa_addr, line));
 
     /* Allow the caller to force the socket family type */
     if (sock_family != -1 && family != sock_family)
@@ -106,7 +106,7 @@ static int findInterfaces(const char* prefixList, char* names, union socketAddre
       // Store the IP address
       int salen = (family == AF_INET) ? sizeof(sockaddr_in) : sizeof(sockaddr_in6);
       memcpy(addrs+found, interface->ifa_addr, salen);
-      INFO(INIT|NET,"NET : Using interface %s:%s", interface->ifa_name, socketToString(interface->ifa_addr, line));
+      INFO(NCCL_INIT|NCCL_NET,"NET : Using interface %s:%s", interface->ifa_name, socketToString(interface->ifa_addr, line));
       found++;
     }
   }
@@ -183,7 +183,7 @@ static int findInterfaceMatchSubnet(char* ifNames, union socketAddress* localAdd
     // Store the interface name
     strncpy(ifNames+found*ifNameMaxSize, interface->ifa_name, ifNameMaxSize);
 
-    INFO(INIT|NET,"NET : Found interface %s:%s in the same subnet as remote address %s", interface->ifa_name, socketToString(&(localAddrs[found].sa), line), socketToString(&(remoteAddr.sa), line_a));
+    INFO(NCCL_INIT|NCCL_NET,"NET : Found interface %s:%s in the same subnet as remote address %s", interface->ifa_name, socketToString(&(localAddrs[found].sa), line), socketToString(&(remoteAddr.sa), line_a));
     found++;
     if (found == maxIfs) break;
   }
@@ -333,7 +333,7 @@ static ncclResult_t createListenSocket(int *fd, union socketAddress *localAddr)
 
 #ifdef ENABLE_TRACE
   char line[1024];
-  TRACE(INIT|NET,"Listening on socket %s", socketToString(&localAddr->sa, line));
+  TRACE(NCCL_INIT|NCCL_NET,"Listening on socket %s", socketToString(&localAddr->sa, line));
 #endif
 
   /* Put the socket in listen mode */
@@ -363,7 +363,7 @@ static ncclResult_t connectAddress(int* fd, union socketAddress* remoteAddr) {
 
 #ifdef ENABLE_TRACE
   char line[1024];
-  TRACE(INIT|NET,"Connecting to socket %s", socketToString(&remoteAddr->sa, line));
+  TRACE(NCCL_INIT|NCCL_NET,"Connecting to socket %s", socketToString(&remoteAddr->sa, line));
 #endif
 
   SYSCHECKNTIMES(connect(*fd, &remoteAddr->sa, salen), "connect", RETRY_TIMES, SLEEP_INT, ECONNREFUSED);
@@ -381,7 +381,7 @@ static ncclResult_t socketReceive(int fd, void* ptr, int size) {
       return ncclSystemError;
     }
     if (recvsize == -1) {
-      INFO(NET,"Recv : got retcode %d, retrying", errno);
+      INFO(NCCL_NET,"Recv : got retcode %d, retrying", errno);
       continue;
     }
     data += recvsize;
@@ -397,7 +397,7 @@ static ncclResult_t socketSend(int fd, void* ptr, int size) {
     int sendsize;
     SYSCHECKVAL(write(fd, data, size-offset), "write", sendsize);
     if (sendsize == -1) {
-      INFO(NET,"Send : got retcode %d, retrying", errno);
+      INFO(NCCL_NET,"Send : got retcode %d, retrying", errno);
       continue;
     }
     data += sendsize;