common/verbs: fix usnic detection

The logic was mishandling the case of a newer kernel and an older
libusnic_verbs.  Simplify usnic_transport() to return constants in the
2 known cases (not a usNIC device and the TRANSPORT_USNIC_UDP case),
and call the magic probe in all other cases.

Reviewed-by: Dave Goodell <dgoodell@cisco.com>

cmr=v1.8.2:reviewer=ompi-rm1.8

This commit was SVN r32260.

ompi/mca/common/verbs/common_verbs_find_ports.c

@@ -268,7 +268,7 @@ static int usnic_magic_probe(struct ibv_context *context)
 }
 
 /*
- * usNIC devices will always return one of three
+ * usNIC devices will always return one of these
  * device->transport_type values:
  *
  * 1. TRANSPORT_IWARP: for older kernels (e.g., on systems such as
@@ -288,7 +288,12 @@ static int usnic_magic_probe(struct ibv_context *context)
  * 3. TRANSPORT_USNIC_UDP: on systems with new kernels and new
  * libibverbs.  In this case, the transport is guaranteed to be
  * usNIC/UDP.
-*/
+ *
+ * 4. TRANSPORT_UNKNOWN: on systems with a new kernel but an old
+ * libibverbs (i.e., kernel understands/returns TRANSPORT_USNIC*
+ * values, but libibverbs doesn't understant the TRANSPORT_USNIC*
+ * constants, and therefore returns TRANSPORT_UNKNOWN).
+ */
 static int usnic_transport(struct ibv_device *device,
                            struct ibv_context *context)
 {
@@ -296,10 +301,6 @@ static int usnic_transport(struct ibv_device *device,
         return USNIC_UNKNOWN;
     }
 
-    if (IBV_TRANSPORT_IWARP == device->transport_type) {
-        return usnic_magic_probe(context);
-    }
-
 #if HAVE_DECL_IBV_TRANSPORT_USNIC_UDP
     /* If we got the transport type of USNIC_UDP, then it's definitely
        the UDP transport. */
@@ -308,15 +309,9 @@ static int usnic_transport(struct ibv_device *device,
     }
 #endif
 
-#if HAVE_DECL_IBV_TRANSPORT_USNIC
-    if (IBV_TRANSPORT_USNIC == device->transport_type) {
-        return usnic_magic_probe(context);
-    }
-#endif
-
-    /* Should never get here -- usnic devices should *always* return
-       one of the 3 above values */
-    return USNIC_UNKNOWN;
+    /* All other cases require a secondary check to figure out whether
+       the transport is L2 or UDP */
+    return usnic_magic_probe(context);
 }
 
 /***********************************************************************/