btl: fix warning about enum type and modify btl_sendi to allow the

value NULL for the descriptor

The send inline optimization uses the btl_sendi function to achieve
lower latency and higher message rates. The problem is the btl_sendi
function was allowed to return a descriptor to the caller. This is fine
for some paths but not ok for the send inline optimization. To fix
this the btl now must be able to handle descriptor = NULL.

opal/mca/btl/btl.h

@@ -279,7 +279,7 @@ enum {
     /** The btl supports atomic bitwise exclusive or */
     MCA_BTL_ATOMIC_SUPPORTS_XOR    = 0x00000800,
     /** The btl supports atomic compare-and-swap */
-    MCA_BTL_ATOMIC_SUPPORTS_CSWAP  = 0x80000000,
+    MCA_BTL_ATOMIC_SUPPORTS_CSWAP  = 0x10000000,
 };
 
 enum mca_btl_base_atomic_op_t {
@@ -839,7 +839,8 @@ typedef int (*mca_btl_base_module_send_fn_t)(
  * @param flags (IN)           Flags.
  * @param tag (IN)             The tag value used to notify the peer.
  * @param descriptor (OUT)     The descriptor to be returned unable to be sent immediately
-
+ *                             (may be NULL).
+ *
  * @retval OPAL_SUCCESS           The send was successfully queued  
  * @retval OPAL_ERROR             The send failed 
  * @retval OPAL_ERR_UNREACH       The endpoint is not reachable 

opal/mca/btl/scif/btl_scif_send.c

@@ -223,7 +223,9 @@ int mca_btl_scif_sendi (struct mca_btl_base_module_t *btl,
 
     rc = mca_btl_scif_send_get_buffer (endpoint, length, &base);
     if (OPAL_UNLIKELY(OPAL_SUCCESS != rc)) {
-        *descriptor = NULL;
+        if (NULL != descriptor) {
+            *descriptor = NULL;
+        }
         return OPAL_ERR_OUT_OF_RESOURCE;
     }
 

opal/mca/btl/sm/btl_sm.c

@@ -947,9 +947,12 @@ int mca_btl_sm_sendi( struct mca_btl_base_module_t* btl,
         return OPAL_SUCCESS;
     }
 
-    /* presumably, this code path will never get executed */
-    *descriptor = mca_btl_sm_alloc( btl, endpoint, order,
-                                    payload_size + header_size, flags);
+    if (NULL != descriptor) {
+        /* presumably, this code path will never get executed */
+        *descriptor = mca_btl_sm_alloc( btl, endpoint, order,
+                                        payload_size + header_size, flags);
+    }
+
     return OPAL_ERR_RESOURCE_BUSY;
 }
 

opal/mca/btl/ugni/btl_ugni_send.c

@@ -135,7 +135,9 @@ int mca_btl_ugni_sendi (struct mca_btl_base_module_t *btl,
         return OPAL_SUCCESS;
     } while (0);
 
-    *descriptor = NULL;
+    if (NULL != descriptor) {
+        *descriptor = NULL;
+    }
     return OPAL_ERR_OUT_OF_RESOURCE;
 }
 

opal/mca/btl/vader/btl_vader_sendi.c

@@ -98,7 +98,9 @@ int mca_btl_vader_sendi (struct mca_btl_base_module_t *btl,
 
     /* write the fragment pointer to peer's the FIFO. the progress function will return the fragment */
     if (!vader_fifo_write_ep (frag->hdr, endpoint)) {
-        *descriptor = &frag->base;
+        if (descriptor) {
+            *descriptor = &frag->base;
+        }
         return OPAL_ERR_OUT_OF_RESOURCE;
     }