DEVICE/API: Update NIXL device API return status (#881)

Signed-off-by: Michal Shalev <mshalev@nvidia.com>

Author: michal-shalev

src/api/gpu/ucx/nixl_device.cuh

@@ -63,7 +63,11 @@ struct nixlGpuXferReqParams {
  */
 __device__ inline nixl_status_t
 nixlGpuConvertUcsStatus(ucs_status_t status) {
-    return status == UCS_OK ? NIXL_SUCCESS : NIXL_ERR_BACKEND;
+    if (!UCS_STATUS_IS_ERR(status)) {
+        return NIXL_SUCCESS;
+    }
+    printf("UCX returned error: %d\n", status);
+    return NIXL_ERR_BACKEND;
 }
 
 /**
@@ -76,7 +80,8 @@ nixlGpuConvertUcsStatus(ucs_status_t status) {
  * @param size          [in]  Size in bytes of the memory to be transferred.
  * @param channel_id    [in]  Channel ID to use for the transfer.
  * @param is_no_delay   [in]  Whether to use no-delay mode.
- * @param xfer_status   [out] Status of the transfer. If null, the status is not reported.
+ * @param xfer_status   [out] Status of the transfer. If not null, use @ref
+ *                            nixlGpuGetXferStatus to check for completion.
  *
  * @return nixl_status_t      Error code if call was not successful
  */
@@ -107,9 +112,10 @@ nixlGpuPostSingleWriteXferReq(nixlGpuXferReqH req_hndl,
  * @param signal_offset      [in]  Offset of the signal to be sent.
  * @param channel_id         [in]  Channel ID to use for the transfer.
  * @param is_no_delay        [in]  Whether to use no-delay mode.
- * @param xfer_status        [out] Status of the transfer. If null, the status is not reported.
+ * @param xfer_status        [out] Status of the transfer. If not null, use @ref
+ *                                 nixlGpuGetXferStatus to check for completion.
  *
- * @return nixl_status_t    Error code if call was not successful
+ * @return nixl_status_t           Error code if call was not successful
  */
 template<nixl_gpu_level_t level = nixl_gpu_level_t::THREAD>
 __device__ nixl_status_t
@@ -143,9 +149,10 @@ nixlGpuPostSignalXferReq(nixlGpuXferReqH req_hndl,
  * @param signal_offset      [in]  Offset of the signal to be sent.
  * @param channel_id         [in]  Channel ID to use for the transfer.
  * @param is_no_delay        [in]  Whether to use no-delay mode.
- * @param xfer_status        [out] Status of the transfer. If null, the status is not reported.
+ * @param xfer_status        [out] Status of the transfer. If not null, use @ref
+ *                                 nixlGpuGetXferStatus to check for completion.
  *
- * @return nixl_status_t    Error code if call was not successful
+ * @return nixl_status_t           Error code if call was not successful
  */
 template<nixl_gpu_level_t level = nixl_gpu_level_t::THREAD>
 __device__ nixl_status_t
@@ -188,9 +195,10 @@ nixlGpuPostPartialWriteXferReq(nixlGpuXferReqH req_hndl,
  * @param signal_offset      [in]  Offset of the signal to be sent.
  * @param channel_id         [in]  Channel ID to use for the transfer.
  * @param is_no_delay        [in]  Whether to use no-delay mode.
- * @param xfer_status        [out] Status of the transfer. If null, the status is not reported.
+ * @param xfer_status        [out] Status of the transfer. If not null, use @ref
+ *                                 nixlGpuGetXferStatus to check for completion.
  *
- * @return nixl_status_t    Error code if call was not successful
+ * @return nixl_status_t           Error code if call was not successful
  */
 template<nixl_gpu_level_t level = nixl_gpu_level_t::THREAD>
 __device__ nixl_status_t
@@ -218,9 +226,9 @@ nixlGpuPostWriteXferReq(nixlGpuXferReqH req_hndl,
  *
  * @param xfer_status [in]  Status of the transfer.
  *
- * @return NIXL_SUCCESS  The request has completed, no more operations are in progress.
- * @return NIXL_IN_PROG  One or more operations in the request have not completed.
- * @return Error code if call was not successful
+ * @return NIXL_SUCCESS     The request has completed, no more operations are in progress.
+ * @return NIXL_IN_PROG     One or more operations in the request have not completed.
+ * @return NIXL_ERR_BACKEND An error occurred in UCX backend.
  */
 template<nixl_gpu_level_t level = nixl_gpu_level_t::THREAD>
 __device__ nixl_status_t