Fix ibv_port_query() usnic extension usage

* Older versions of libusnic_verbs actually return 0 when querying for
  an unknown port.  So also check for a magic ID in the returned data
  to *really* know if the usnic extensions are supported.
* Use a union (in the common_verbs area) and memcpy (in the btl) to
  avoid undefined C type aliasing behavior.
* Ensure to memset the function table to 0 if the usnic extensions
  are not supported.

Submitted by Jeff Squyres, reviewed by Dave Goodell.

cmr=v1.7.5:reviewer=ompi-rm1.7

This commit was SVN r30935.

ompi/mca/btl/usnic/btl_usnic_ext.c

@@ -30,11 +30,21 @@ void ompi_btl_usnic_ext_init(struct ibv_context *context)
     memset(&ompi_btl_usnic_ext, 0, sizeof(ompi_btl_usnic_ext));
 
     /* See if this context supports the usnic extensions.  Do the
-       magic query port on port number 42 (which is THE ANSWER) */
+       magic query port on port number 42 (which is THE ANSWER).  If
+       it works, we'll get rc==0 and the magic number in the struct
+       will be set.  Note, however, that due to a bug in early
+       versions of libusnic_verbs, we *may* get rc==0 even if it
+       doesn't work, which is why we also must check for the magic
+       value, too. */
     int rc;
-    rc = ibv_query_port(context, 42,
+    struct ibv_port_attr attr;
-                        (struct ibv_port_attr*) &ompi_btl_usnic_ext.qpt);
+    rc = ibv_query_port(context, 42, &attr);
-    if (0 != rc) {
+    assert(sizeof(ompi_btl_usnic_ext) <= sizeof(attr));
+    memcpy(&ompi_btl_usnic_ext, &attr, sizeof(ompi_btl_usnic_ext));
+    if (0 != rc || USNIC_PORT_QUERY_MAGIC != ompi_btl_usnic_ext.qpt.magic) {
+        /* If the probe fails, we must re-memset() the function
+           pointer block */
+        memset(&ompi_btl_usnic_ext, 0, sizeof(ompi_btl_usnic_ext));
         opal_output_verbose(5, USNIC_OUT,
                             "btl:usnic: verbs plugin does not support extensions");
         return;
@@ -50,6 +60,9 @@ void ompi_btl_usnic_ext_init(struct ibv_context *context)
                         "btl:usnic: verbs plugin has extension lookup ABI version %d",
                         ompi_btl_usnic_ext.qpt.lookup_version);
     if (1 != ompi_btl_usnic_ext.qpt.lookup_version) {
+        /* If the probe fails, we must re-memset() the function
+           pointer block, because it may/will return junk in the qpt */
+        memset(&ompi_btl_usnic_ext, 0, sizeof(ompi_btl_usnic_ext));
         opal_output_verbose(5, USNIC_OUT,
                             "btl:usnic: unrecognized lookup ABI version"
                             " (I only recognize version 1) "

ompi/mca/btl/usnic/btl_usnic_ext.h

@@ -14,13 +14,18 @@
 
 #include <infiniband/verbs.h>
 
+#include "opal_stdint.h"
+
 typedef void *(*ompi_btl_usnic_dlsym_fn_t)(const char *name);
 
 typedef struct {
     int lookup_version;
+    uint64_t magic;
     ompi_btl_usnic_dlsym_fn_t lookup;
 } ompi_btl_usnic_query_port_table_t;
 
+#define USNIC_PORT_QUERY_MAGIC (0x43494e7375534355ULL)
+
 /*
  * Tells libusnic_verbs to enable UDP support.
  */

ompi/mca/common/verbs/common_verbs_find_ports.c

@@ -232,6 +232,20 @@ enum {
     USNIC_UNKNOWN
 };
 
+/* See comment in btl_usnic_ext.c about why we must check the return
+   from the usnic verbs extensions probe for a magic number (which
+   means we must also copy the usnic extension struct and magic number
+   value down here into common/verbs.  Bummer). */
+typedef union {
+    struct {
+        int lookup_version;
+        uint64_t magic;
+    } qpt;
+    struct ibv_port_attr attr;
+} port_query_u;
+
+#define USNIC_PORT_QUERY_MAGIC (0x43494e7375534355ULL)
+
 /*
  * usNIC devices will always return one of three
  * device->transport_type values:
@@ -269,10 +283,18 @@ static int usnic_transport(struct ibv_device *device,
        here. */
     if (IBV_TRANSPORT_IWARP == device->transport_type) {
         int rc;
-        struct ibv_port_attr attr;
+        port_query_u u;
-        rc = ibv_query_port(context, 42, &attr);
+        rc = ibv_query_port(context, 42, &u.attr);
-        if (0 == rc) {
+        /* See comment in btl_usnic_ext.c about why we have to check
+           for rc==0 *and* the magic number. */
+        if (0 == rc && USNIC_PORT_QUERY_MAGIC == u.qpt.magic) {
+            /* We only support version 1 of the lookup function in
+               this particular version of Open MPI */
+            if (1 == u.qpt.lookup_version) {
                 return USNIC_UDP;
+            } else {
+                return USNIC_UNKNOWN;
+            }
         } else {
             return USNIC_L2;
         }