text: /* -*- Mode: C; c-basic-offset:4 ; -*- */
  /*
   * Copyright (c) 2004-2007 The Trustees of Indiana University and Indiana
   *                         University Research and Technology
   *                         Corporation.  All rights reserved.
   * Copyright (c) 2004-2008 The University of Tennessee and The University
   *                         of Tennessee Research Foundation.  All rights
   *                         reserved.
   * Copyright (c) 2004-2005 High Performance Computing Center Stuttgart, 
   *                         University of Stuttgart.  All rights reserved.
   * Copyright (c) 2004-2005 The Regents of the University of California.
   *                         All rights reserved.
   * Copyright (c) 2006-2007 Los Alamos National Security, LLC.  All rights
   *                         reserved. 
   * Copyright (c) 2010      Oracle and/or its affiliates.  All rights reserved.
   * Copyright (c) 2012      NVIDIA Corporation.  All rights reserved.
   * $COPYRIGHT$
   * 
   * Additional copyrights may follow
   * 
   * $HEADER$
   */
  /**
   * @file
   *
   * Byte Transfer Layer (BTL)
   *
   *
   * BTL Initialization:
   *
   * During library initialization, all available BTL components are
   * loaded and opened via their mca_base_open_component_fn_t
   * function. The BTL open function should register any mca parameters
   * used to tune/adjust the behaviour of the BTL (mca_base_param_register_int(),
   * mca_base_param_register_string()). Note that the open function may fail
   * if the resources (e.g. shared libraries, etc) required by the network
   * transport are not available.
   *
   * The mca_btl_base_component_init_fn_t() is then called for each of the
   * components that are succesfully opened. The component init function may
   * return either:
   *
   * (1) a NULL list of BTL modules if the transport is not available,
   * (2) a list containing a one or more single BTL modules, where the BTL provides
   *     a layer of abstraction over one or more physical devices (e.g. NICs),
   *
   * During module initialization, the module should post any addressing
   * information required by its peers. An example would be the TCP
   * listen port opened by the TCP module for incoming connection
   * requests. This information is published to peers via the
   * ompi_modex_send() interface. Note that peer information is not
   * guaranteed to be available via ompi_modex_recv() during the
   * module's init function. However, it will be available during
   * BTL selection (mca_btl_base_add_proc_fn_t()).
   *
   * BTL Selection:
   *
   * The upper layer builds an ordered list of the available BTL modules sorted
   * by their exclusivity ranking. This is a relative ranking that is used
   * to determine the set of BTLs that may be used to reach a given destination.
   * During startup the BTL modules are queried via their
   * mca_btl_base_add_proc_fn_t() to determine if they are able to reach
   * a given destination.  The BTL module with the highest ranking that
   * returns success is selected. Subsequent BTL modules are selected only
   * if they have the same exclusivity ranking.
   *
   * An example of how this might be used:
   *
   * BTL         Exclusivity   Comments
   * --------    -----------   ------------------
   * LO              100       Selected exclusively for local process
   * SM               50       Selected exclusively for other processes on host
   * IB                0       Selected based on network reachability
   * IB                0       Selected based on network reachability
   * TCP               0       Selected based on network reachability
   * TCP               0       Selected based on network reachability
   *
   * When mca_btl_base_add_proc_fn_t() is called on a  BTL module, the BTL 
   * will populate an OUT variable with mca_btl_base_endpoint_t pointers. 
   * Each pointer is treated as an opaque handle by the upper layer and is
   * returned to the BTL on subsequent data transfer calls to the
   * corresponding destination process.  The actual contents of the
   * data structure are defined on a per BTL basis, and may be used to
   * cache addressing or connection information, such as a TCP socket
   * or IB queue pair.
   *
   * Progress:
   *
   * By default, the library provides for polling based progress of outstanding
   * requests. The BTL component exports an interface function (btl_progress)
   * that is called in a polling mode by the PML during calls into the MPI
   * library. Note that the btl_progress() function is called on the BTL component
   * rather than each BTL module. This implies that the BTL author is responsible
   * for iterating over the pending operations in each of the BTL modules associated
   * with the component.
   *
   * On platforms where threading support is provided, the library provides the
   * option of building with asynchronous threaded progress. In this case, the BTL
   * author is responsible for providing a thread to progress pending operations.
   * A thread is associated with the BTL component/module such that transport specific
   * functionality/APIs may be used to block the thread until a pending operation
   * completes. This thread MUST NOT poll for completion as this would oversubscribe
   * the CPU.
   *
   * Note that in the threaded case the PML may choose to use a hybrid approach,
   * such that polling is implemented from the user thread for a fixed number of
   * cycles before relying on the background thread(s) to complete requests. If
   * possible the BTL should support the use of both modes concurrently.
   *
   */
  
  #ifndef MCA_BTL_H
  #define MCA_BTL_H
  
  #include "ompi_config.h"
  #include "opal/mca/mca.h"
  #include "opal/class/opal_bitmap.h"
  #include "opal/datatype/opal_convertor.h"
  #include "opal/prefetch.h" /* For OPAL_LIKELY */
  #include "ompi/mca/mpool/mpool.h"
  #include "ompi/types.h"
  #include "opal/types.h"
  
  #include "opal/mca/crs/crs.h"
  #include "opal/mca/crs/base/base.h"
  
  BEGIN_C_DECLS
  
  /*
   * BTL types
   */
  
  struct mca_btl_base_module_t;
  struct mca_btl_base_endpoint_t;
  struct mca_btl_base_descriptor_t;
  struct mca_mpool_base_resources_t;
  struct ompi_proc_t; 
  
  
  /* send/recv operations require tag matching */
  typedef uint8_t mca_btl_base_tag_t;
  
  #define MCA_BTL_NO_ORDER       255
  
  /*
   * Communication specific defines. There are a number of active message ID
   * that can be shred between all frameworks that need to communicate (i.e.
   * use the PML or the BTL directly). These ID are exchanged between the
   * processes, therefore they need to be identical everywhere. The simplest
   * approach is to have them defined as constants, and give each framework a
   * small number. Here is the rule that defines these ID (they are 8 bits):
   * - the first 3 bits are used to code the framework (i.e. PML, OSC, COLL)
   * - the remaining 5 bytes are used internally by the framework, and divided
   *   based on the components requirements. Therefore, the way the PML and
   * the OSC frameworks use these defines will be different. For more
   * information about how these framework ID are defined, take a look in the
   * header file associated with the framework.
   */
  #define MCA_BTL_AM_FRAMEWORK_MASK   0xD0
  #define MCA_BTL_TAG_BTL             0x20
  #define MCA_BTL_TAG_PML             0x40
  #define MCA_BTL_TAG_OSC_RDMA        0x60
  #define MCA_BTL_TAG_USR             0x80
  #define MCA_BTL_TAG_MAX             255 /* 1 + highest allowed tag num */
  
  /*
   * Reserved tags for specific BTLs. As multiple BTLs can be active
   * simultaneously, their tags should not collide.
   */
  #define MCA_BTL_TAG_IB                (MCA_BTL_TAG_BTL + 0)
  #define MCA_BTL_TAG_UDAPL             (MCA_BTL_TAG_BTL + 1)
  
  /* prefered protocol */
  #define MCA_BTL_FLAGS_SEND            0x0001
  #define MCA_BTL_FLAGS_PUT             0x0002
  #define MCA_BTL_FLAGS_GET             0x0004
  #define MCA_BTL_FLAGS_RDMA (MCA_BTL_FLAGS_GET|MCA_BTL_FLAGS_PUT)
  
  /* btl can send directly from user buffer w/out registration */
  #define MCA_BTL_FLAGS_SEND_INPLACE    0x0008
  
  /* btl transport reliability flags - currently used only by the DR PML */
  #define MCA_BTL_FLAGS_NEED_ACK        0x0010
  #define MCA_BTL_FLAGS_NEED_CSUM       0x0020
  
  /** RDMA put/get calls must have a matching prepare_{src,dst} call
      on the target with the same base (and possibly bound). */
  #define MCA_BTL_FLAGS_RDMA_MATCHED    0x0040
  
  /* btl needs local rdma completion */
  #define MCA_BTL_FLAGS_RDMA_COMPLETION 0x0080
  
   /* btl can do heterogeneous rdma operations on byte buffers */
  #define MCA_BTL_FLAGS_HETEROGENEOUS_RDMA 0x0100
  
  /* btl can support failover if enabled */
  #define MCA_BTL_FLAGS_FAILOVER_SUPPORT 0x0200
  
  #define MCA_BTL_FLAGS_CUDA_PUT        0x0400
  #define MCA_BTL_FLAGS_CUDA_GET        0x0800
  #define MCA_BTL_FLAGS_CUDA_RDMA (MCA_BTL_FLAGS_CUDA_GET|MCA_BTL_FLAGS_CUDA_PUT)
  
  /* Default exclusivity levels */
  #define MCA_BTL_EXCLUSIVITY_HIGH     (64*1024) /* internal loopback */
  #define MCA_BTL_EXCLUSIVITY_DEFAULT  1024      /* GM/IB/etc. */
  #define MCA_BTL_EXCLUSIVITY_LOW      0         /* TCP used as a last resort */
  
  /* error callback flags */
  #define MCA_BTL_ERROR_FLAGS_FATAL 0x1
  #define MCA_BTL_ERROR_FLAGS_NONFATAL 0x2
  
  /**
   * Asynchronous callback function on completion of an operation.
   * Completion Semantics: The descriptor can be reused or returned to the 
   *  BTL via mca_btl_base_module_free_fn_t. The operation has been queued to
   *  the network device or will otherwise make asynchronous progress without 
   *  subsequent calls to btl_progress.
   *
   * @param[IN] module      the BTL module
   * @param[IN] endpoint    the BTL endpoint
   * @param[IN] descriptor  the BTL descriptor
   *
   */
  typedef void (*mca_btl_base_completion_fn_t)(
      struct mca_btl_base_module_t* module,
      struct mca_btl_base_endpoint_t* endpoint,
      struct mca_btl_base_descriptor_t* descriptor,
      int status);
  
  /**
   * Describes a region/segment of memory that is addressable 
   * by an BTL.
   *
   * Note: In many cases the alloc and prepare methods of BTLs
   * do not return a mca_btl_base_segment_t but instead return a
   * subclass. Extreme care should be used when modifying
   * BTL segments to prevent overwriting internal BTL data.
   *
   * All BTLs MUST use base segments when calling registered
   * Callbacks.
   *
   * BTL MUST use mca_btl_base_segment_t or a subclass and
   * MUST store their segment length in btl_seg_size. BTLs
   * MIST specify a segment no larger than MCA_BTL_SEG_MAX_SIZE.
   *
   */
  
  struct mca_btl_base_segment_t {
      /** Address of the memory */
      ompi_ptr_t seg_addr;        
       /** Length in bytes */
      uint64_t   seg_len;
  };
  typedef struct mca_btl_base_segment_t mca_btl_base_segment_t;
  
  /**
   * A descriptor that holds the parameters to a send/put/get
   * operation along w/ a callback routine that is called on
   * completion of the request.
   * Note: from the initiator of a PUT operation des_src is the local memory 
   *       and des_dst is the remote memory 
   *       from the initiator of a GET operations des_dst is the local memory 
   *       and des_src is the remote memory 
   *       from the initiator of a SEND operation des_src is the local memory
   *       and des_dst is not used
   */
  
  struct mca_btl_base_descriptor_t {
      ompi_free_list_item_t super;  
      mca_btl_base_segment_t *des_src;    /**< source segments */
      size_t des_src_cnt;                 /**< number of source segments */
      mca_btl_base_segment_t *des_dst;    /**< destination segments */
      size_t des_dst_cnt;                 /**< number of destination segments */
      mca_btl_base_completion_fn_t des_cbfunc;  /**< local callback function */ 
      void* des_cbdata;                         /**< opaque callback data */
      void* des_context;                        /**< more opaque callback data */
      uint32_t des_flags;                       /**< hints to BTL */
      /** order value, this is only 
          valid in the local completion callback 
          and may be used in subsequent calls to 
          btl_alloc, btl_prepare_src/dst to request 
          a descriptor that will be ordered w.r.t. 
          this descriptor
      */
      uint8_t order;                            
  };
  typedef struct mca_btl_base_descriptor_t mca_btl_base_descriptor_t;
  
  OMPI_DECLSPEC OBJ_CLASS_DECLARATION(mca_btl_base_descriptor_t);
  
  #define MCA_BTL_DES_FLAGS_PRIORITY          0x0001
  /* Allow the BTL to dispose the descriptor once the callback
   * associated was triggered.
   */
  #define MCA_BTL_DES_FLAGS_BTL_OWNERSHIP     0x0002
  /* Allow the BTL to avoid calling the descriptor callback
   * if the send succeded in the btl_send (i.e in the fast path).
   */
  #define MCA_BTL_DES_SEND_ALWAYS_CALLBACK    0x0004
  
  /* Type of transfer that will be done with this frag.
   */
  #define MCA_BTL_DES_FLAGS_PUT               0x0010
  #define MCA_BTL_DES_FLAGS_GET               0x0020
  
  /**
   * Maximum number of allowed segments in src/dst fields of a descriptor.
   */
  #define MCA_BTL_DES_MAX_SEGMENTS 16
  
  /**
   * Maximum size of a BTL segment (NTH: does it really save us anything
   * to hardcode this?)
   */
  #define MCA_BTL_SEG_MAX_SIZE 256
  
  /* 
   *  BTL base header, stores the tag at a minimum 
   */ 
  struct mca_btl_base_header_t{ 
      mca_btl_base_tag_t tag; 
  }; 
  typedef struct mca_btl_base_header_t mca_btl_base_header_t; 
  
  #define MCA_BTL_BASE_HEADER_HTON(hdr)
  #define MCA_BTL_BASE_HEADER_NTOH(hdr)
  
  /*
   *  BTL component interface functions and datatype.
   */
  
  /**
   * MCA->BTL Initializes the BTL component and creates specific BTL
   * module(s).
   *
   * @param num_btls (OUT) Returns the number of btl modules created, or 0
   *                       if the transport is not available.
   *
   * @param enable_progress_threads (IN) Whether this component is
   * allowed to run a hidden/progress thread or not.
   *
   * @param enable_mpi_threads (IN) Whether support for multiple MPI
   * threads is enabled or not (i.e., MPI_THREAD_MULTIPLE), which
   * indicates whether multiple threads may invoke this component
   * simultaneously or not.
   *
   * @return Array of pointers to BTL modules, or NULL if the transport  
   *         is not available.
   *
   * During component initialization, the BTL component should discover
   * the physical devices that are available for the given transport,
   * and create a BTL module to represent each device. Any addressing 
   * information required by peers to reach the device should be published 
   * during this function via the ompi_modex_send() interface. 
   *
   */
  
  typedef struct mca_btl_base_module_t** (*mca_btl_base_component_init_fn_t)(
      int *num_btls, 
      bool enable_progress_threads,
      bool enable_mpi_threads
  );
  
  /**
   * MCA->BTL Called to progress outstanding requests for
   * non-threaded polling environments.
   *
   * @return           Count of "completions", a metric of 
   *                   how many items where completed in the call 
   *                   to progress.
   */
  
  typedef int (*mca_btl_base_component_progress_fn_t)(void);
  
  
  /**
   * Callback function that is called asynchronously on receipt
   * of data by the transport layer. 
   * Note that the the mca_btl_base_descriptor_t is only valid within the 
   * completion function, this implies that all data payload in the 
   * mca_btl_base_descriptor_t must be copied out within this callback or 
   * forfeited back to the BTL.
   * Note also that descriptor segments (des_dst, des_src) must be base
   * segments for all callbacks.
   * 
   * @param[IN] btl        BTL module
   * @param[IN] tag        The active message receive callback tag value 
   * @param[IN] descriptor The BTL descriptor (contains the receive payload) 
   * @param[IN] cbdata     Opaque callback data
   */
  
  typedef void (*mca_btl_base_module_recv_cb_fn_t)(
      struct mca_btl_base_module_t* btl, 
      mca_btl_base_tag_t tag,
      mca_btl_base_descriptor_t* descriptor,
      void* cbdata
  );
  
  typedef struct mca_btl_active_message_callback_t {
      mca_btl_base_module_recv_cb_fn_t cbfunc;
      void* cbdata;
  } mca_btl_active_message_callback_t;
  
  OMPI_DECLSPEC extern
  mca_btl_active_message_callback_t mca_btl_base_active_message_trigger[MCA_BTL_TAG_MAX];
  
  /**
   *  BTL component descriptor. Contains component version information
   *  and component open/close/init functions.
   */
  
  struct mca_btl_base_component_2_0_0_t {
    mca_base_component_t btl_version;
    mca_base_component_data_t btl_data;
    mca_btl_base_component_init_fn_t btl_init;
    mca_btl_base_component_progress_fn_t btl_progress;
  };
  typedef struct mca_btl_base_component_2_0_0_t mca_btl_base_component_2_0_0_t;
  typedef struct mca_btl_base_component_2_0_0_t mca_btl_base_component_t;
  
  /*  add the 1_0_0_t typedef for source compatibility 
   *  we can do this safely because 1_0_0 components are the same as 
   *  1_0_1 components, the difference is in the btl module. 
   *  Fortunately the only difference in the module is an additional interface
   *  function added to 1_0_1. We can therefore safely treat an older module just
   *  just like the new one so long as we check the component version 
   *  prior to invoking the new interface function.
   */
  typedef struct mca_btl_base_component_2_0_0_t mca_btl_base_component_1_0_1_t;
  typedef struct mca_btl_base_component_2_0_0_t mca_btl_base_component_1_0_0_t;
  
  
  
  /*
   * BTL module interface functions and datatype.
   */
  
  /**
   * MCA->BTL Clean up any resources held by BTL module 
   * before the module is unloaded.
   *  
   * @param btl (IN)   BTL module.
   * @return           OMPI_SUCCESS or error status on failure.
   *
   * Prior to unloading a BTL module, the MCA framework will call 
   * the BTL finalize method of the module. Any resources held by 
   * the BTL should be released and if required the memory corresponding
   * to the BTL module freed.
   * 
   */
  typedef int (*mca_btl_base_module_finalize_fn_t)(
      struct mca_btl_base_module_t* btl
  );
                                                                                                           
  /**
   * BML->BTL notification of change in the process list. 
   *
   * @param btl (IN)            BTL module
   * @param nprocs (IN)         Number of processes
   * @param procs (IN)          Array of processes
   * @param endpoint (OUT)      Array of mca_btl_base_endpoint_t structures by BTL.
   * @param reachable (OUT)     Bitmask indicating set of peer processes that are reachable by this BTL.
   * @return                    OMPI_SUCCESS or error status on failure.
   *
   * The mca_btl_base_module_add_procs_fn_t() is called by the BML to 
   * determine the set of BTLs that should be used to reach each process.
   * Any addressing information exported by the peer via the ompi_modex_send()
   * function should be available during this call via the corresponding 
   * ompi_modex_recv() function. The BTL may utilize this information to 
   * determine reachability of each peer process. 
   *
   * For each process that is reachable by the BTL, the bit corresponding to the index 
   * into the proc array (nprocs) should be set in the reachable bitmask. The BTL 
   * will return an array of pointers to a data structure defined
   * by the BTL that is then returned to the BTL on subsequent calls to the BTL data
   * transfer functions (e.g btl_send). This may be used by the BTL to cache any addressing 
   * or connection information (e.g. TCP socket, IB queue pair).
   */
  typedef int (*mca_btl_base_module_add_procs_fn_t)(
      struct mca_btl_base_module_t* btl, 
      size_t nprocs,
      struct ompi_proc_t** procs, 
      struct mca_btl_base_endpoint_t** endpoints,
      struct opal_bitmap_t* reachable
  );
  
  /**
   * Notification of change to the process list.
   *
   * @param btl (IN)     BTL module
   * @param nprocs (IN)  Number of processes
   * @param proc (IN)    Set of processes
   * @param peer (IN)    Set of peer addressing information.
   * @return             Status indicating if cleanup was successful
   *
   * When the process list changes, the BML notifies the BTL of the
   * change, to provide the opportunity to cleanup or release any
   * resources associated with the peer.
   */
  typedef int (*mca_btl_base_module_del_procs_fn_t)(
      struct mca_btl_base_module_t* btl, 
      size_t nprocs,
      struct ompi_proc_t** procs, 
      struct mca_btl_base_endpoint_t** peer
  );
  
  /**
   * Register a callback function that is called on receipt
   * of a fragment.
   *
   * @param[IN] btl      BTL module
   * @param[IN] tag      tag value of this callback 
   *                     (specified on subsequent send operations)
   * @param[IN] cbfunc   The callback function
   * @param[IN] cbdata   Opaque callback data 
   * 
   * @return OMPI_SUCCESS The callback was registered successfully
   * @return OMPI_ERROR   The callback was NOT registered successfully
   *
   */
  typedef int (*mca_btl_base_module_register_fn_t)(
      struct mca_btl_base_module_t* btl, 
      mca_btl_base_tag_t tag,
      mca_btl_base_module_recv_cb_fn_t cbfunc,
      void* cbdata
  );
  
  
  /**
   * Callback function that is called asynchronously on receipt
   * of an error from the transport layer 
   *
   * @param[IN] btl     BTL module
   * @param[IN] flags   type of error 
   * @param[IN] errproc process that had an error
   * @param[IN] btlinfo descriptive string from the BTL
   */
  
  typedef void (*mca_btl_base_module_error_cb_fn_t)(
          struct mca_btl_base_module_t* btl,
          int32_t flags,
          struct ompi_proc_t* errproc,
          char* btlinfo
  );
  
  
  /**
   * Register a callback function that is called on receipt
   * of an error.
   *
   * @param[IN] btl       BTL module
   * @param[IN] cbfunc    The callback function
   *
   * @return OMPI_SUCCESS The callback was registered successfully
   * @return OMPI_ERROR   The callback was NOT registered successfully
   *
   */
  typedef int (*mca_btl_base_module_register_error_fn_t)(
      struct mca_btl_base_module_t* btl, 
      mca_btl_base_module_error_cb_fn_t cbfunc
  );
  
  
  /**
   * Allocate a descriptor with a segment of the requested size. 
   * Note that the BTL layer may choose to return a smaller size
   * if it cannot support the request. The order tag value ensures that
   * operations on the descriptor that is allocated will be 
   * ordered w.r.t. a previous operation on a particular descriptor. 
   * Ordering is only guaranteed if the previous descriptor had its 
   * local completion callback function called and the order tag of 
   * that descriptor is only valid upon the local completion callback function.
   * 
   *
   * @param btl (IN)      BTL module
   * @param size (IN)     Request segment size.
   * @param order (IN)    The ordering tag (may be MCA_BTL_NO_ORDER)
   */
  
  typedef mca_btl_base_descriptor_t* (*mca_btl_base_module_alloc_fn_t)(
      struct mca_btl_base_module_t* btl,
      struct mca_btl_base_endpoint_t* endpoint,
      uint8_t order,
      size_t size,
      uint32_t flags
  );
  
  /**
   * Return a descriptor allocated from this BTL via alloc/prepare.
   * A descriptor can only be deallocated after its local completion 
   * callback function has called for all send/put/get operations.
   * 
   * @param btl (IN)      BTL module
   * @param segment (IN)  Descriptor allocated from the BTL
   */
  typedef int (*mca_btl_base_module_free_fn_t)(
      struct mca_btl_base_module_t* btl,
      mca_btl_base_descriptor_t* descriptor
  );
  
  
  /**
   * Prepare a descriptor for send/put/get using the supplied
   * convertor. If the convertor references data that is contiguous,
   * the descriptor may simply point to the user buffer. Otherwise,
   * this routine is responsible for allocating buffer space and
   * packing if required.
   *
   * The descriptor returned can be used in multiple concurrent operations 
   * (send/put/get) unless the BTL has the MCA_BTL_FLAGS_RDMA_MATCHED flag set 
   * in which case a corresponding prepare call must accompany the put/get call
   * in addition, the address and length that is put/get must match the address 
   * and length which is prepared.
   *
   * The order tag value ensures that operations on the 
   * descriptor that is prepared will be ordered w.r.t. a previous
   * operation on a particular descriptor. Ordering is only guaranteed if 
   * the previous descriptor had its local completion callback function 
   * called and the order tag of that descriptor is only valid upon the local 
   * completion callback function.
   *
   * @param btl (IN)          BTL module
   * @param endpoint (IN)     BTL peer addressing
   * @param registration (IN) Memory registration
   * @param convertor (IN)    Data type convertor
   * @param order (IN)        The ordering tag (may be MCA_BTL_NO_ORDER)
   * @param reserve (IN)      Additional bytes requested by upper layer to precede user data
   * @param size (IN/OUT)     Number of bytes to prepare (IN),
   *                          number of bytes actually prepared (OUT)
   *
   */
  typedef struct mca_btl_base_descriptor_t* (*mca_btl_base_module_prepare_fn_t)(
      struct mca_btl_base_module_t* btl,
      struct mca_btl_base_endpoint_t* endpoint,
      mca_mpool_base_registration_t* registration,
      struct opal_convertor_t* convertor,
      uint8_t order,
      size_t reserve,
      size_t* size,
      uint32_t flags
  );
  
  /**
   * Initiate an asynchronous send.
   * Completion Semantics: the descriptor has been queued for a send operation
   *                       the BTL now controls the descriptor until local 
   *                       completion callback is made on the descriptor
   *                       
   * All BTLs allow multiple concurrent asynchronous send operations on a descriptor
   *
   * @param btl (IN)         BTL module
   * @param endpoint (IN)    BTL addressing information
   * @param descriptor (IN)  Description of the data to be transfered
   * @param tag (IN)         The tag value used to notify the peer.
   * 
   * @retval OMPI_SUCCESS    The descriptor was successfully queued for a send 
   * @retval OMPI_ERROR      The descriptor was NOT successfully queued for a send 
   * @retval OMPI_ERR_UNREACH The endpoint is not reachable 
   */
  typedef int (*mca_btl_base_module_send_fn_t)(
      struct mca_btl_base_module_t* btl,
      struct mca_btl_base_endpoint_t* endpoint,
      struct mca_btl_base_descriptor_t* descriptor,
      mca_btl_base_tag_t tag
  );
  
  /**
   * Initiate an immediate blocking send. 
   * Completion Semantics: the BTL will make a best effort 
   *  to send the header and "size" bytes from the datatype using the convertor. 
   *  The header is guaranteed to be delivered entirely in the first segment. 
   *  Should the BTL be unable to deliver the data due to resource constraints 
   *  the BTL will return a descriptor (via the OUT param) 
   *  of size "payload_size + header_size".
   *
   * @param btl (IN)             BTL module
   * @param endpoint (IN)        BTL addressing information
   * @param convertor (IN)       Data type convertor
   * @param header (IN)          Pointer to header.
   * @param header_size (IN)     Size of header.
   * @param payload_size (IN)    Size of payload (from convertor).
   * @param order (IN)           The ordering tag (may be MCA_BTL_NO_ORDER)
   * @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
  
   * @retval OMPI_SUCCESS           The send was successfully queued  
   * @retval OMPI_ERROR             The send failed 
   * @retval OMPI_ERR_UNREACH       The endpoint is not reachable 
   * @retval OMPI_ERR_RESOURCE_BUSY The BTL is busy a descriptor will be returned 
   *                                (via the OUT param) if descriptors are available 
  
   */
  
  typedef int (*mca_btl_base_module_sendi_fn_t)(
      struct mca_btl_base_module_t* btl,
      struct mca_btl_base_endpoint_t* endpoint,
      struct opal_convertor_t* convertor,
      void* header,
      size_t header_size,
      size_t payload_size,
      uint8_t order,
      uint32_t flags,
      mca_btl_base_tag_t tag,
      mca_btl_base_descriptor_t** descriptor
   );
  
  /**
   * Initiate an asynchronous put. 
   * Completion Semantics: the descriptor has been queued for a put operation
   *                       the BTL now controls the descriptor until local 
   *                       completion callback is made on the descriptor
   *
   * BTLs that do not have the MCA_BTL_FLAGS_RDMA_MATCHED flag set 
   *  allow multiple concurrent put operations on the same descriptor. 
   * BTLs that do have the MCA_BTL_FLAGS_RDMA_MATCHED  flag set require 
   *  a corresponding prepare_src/dst call for each put operation and 
   *  therefore prohibit multiple concurrent put operations.
   * 
   * @param btl (IN)         BTL module
   * @param endpoint (IN)    BTL addressing information
   * @param descriptor (IN)  Description of the data to be transferred
   * 
   * @retval OMPI_SUCCESS    The descriptor was successfully queued for a put
   * @retval OMPI_ERROR      The descriptor was NOT successfully queued for a put
   */
  
  typedef int (*mca_btl_base_module_put_fn_t)(
      struct mca_btl_base_module_t* btl,
      struct mca_btl_base_endpoint_t* endpoint,
      struct mca_btl_base_descriptor_t* descriptor
  );
  
  /**
   * Initiate an asynchronous get.
   *
   * Completion Semantics: the descriptor has been queued for a get operation
   *                       the BTL now controls the descriptor until local 
   *                       completion callback is made on the descriptor
   *
   * BTLs that do not have the MCA_BTL_FLAGS_RDMA_MATCHED flag set 
   *  allow multiple concurrent get operations on the same descriptor. 
   * BTLs that do have the MCA_BTL_FLAGS_RDMA_MATCHED  flag set require 
   *  a corresponding prepare_src/dst call for each get operation and 
   *  therefore prohibit multiple concurrent get operations.
   *
   * @param btl (IN)         BTL module
   * @param endpoint (IN)    BTL addressing information
   * @param descriptor (IN)  Description of the data to be transferred
   * 
   * @retval OMPI_SUCCESS    The descriptor was successfully queued for a get
   * @retval OMPI_ERROR      The descriptor was NOT successfully queued for a get
   *
   */
  
  typedef int (*mca_btl_base_module_get_fn_t)(
      struct mca_btl_base_module_t* btl,
      struct mca_btl_base_endpoint_t* endpoint,
      struct mca_btl_base_descriptor_t* descriptor
  );
  
  
  /**
   * Diagnostic dump of btl state.
   *
   * @param btl (IN)         BTL module
   * @param endpoint (IN)    BTL endpoint
   * @param verbose (IN)     Verbosity level
   */
  
  typedef void (*mca_btl_base_module_dump_fn_t)(
      struct mca_btl_base_module_t* btl,
      struct mca_btl_base_endpoint_t* endpoint,
      int verbose
  );
  
  /**
   * Fault Tolerance Event Notification Function
   * @param state Checkpoint Status
   * @return OMPI_SUCCESS or failure status
   */
  typedef int (*mca_btl_base_module_ft_event_fn_t)(int state);
  
  /**
   * BTL module interface functions and attributes.
   */
  struct mca_btl_base_module_t {
  
      /* BTL common attributes */
      mca_btl_base_component_t* btl_component; /**< pointer back to the BTL component structure */
      size_t      btl_eager_limit;      /**< maximum size of first fragment -- eager send */
      size_t      btl_rndv_eager_limit;    /**< the size of a data sent in a first fragment of rendezvous protocol */
      size_t      btl_max_send_size;    /**< maximum send fragment size supported by the BTL */
      size_t      btl_rdma_pipeline_send_length; /**< amount of bytes that should be send by pipeline protocol */
      size_t      btl_rdma_pipeline_frag_size; /**< maximum rdma fragment size supported by the BTL */
      size_t      btl_min_rdma_pipeline_size; /**< minimum packet size for pipeline protocol  */
      uint32_t    btl_exclusivity;      /**< indicates this BTL should be used exclusively */
      uint32_t    btl_latency;          /**< relative ranking of latency used to prioritize btls */
      uint32_t    btl_bandwidth;        /**< bandwidth (Mbytes/sec) supported by each endpoint */
      uint32_t    btl_flags;            /**< flags (put/get...) */
      size_t      btl_seg_size;         /**< size of a btl segment */
  
      /* BTL function table */
      mca_btl_base_module_add_procs_fn_t      btl_add_procs;
      mca_btl_base_module_del_procs_fn_t      btl_del_procs;
      mca_btl_base_module_register_fn_t       btl_register;
      mca_btl_base_module_finalize_fn_t       btl_finalize;
  
      mca_btl_base_module_alloc_fn_t          btl_alloc;
      mca_btl_base_module_free_fn_t           btl_free;
      mca_btl_base_module_prepare_fn_t        btl_prepare_src;
      mca_btl_base_module_prepare_fn_t        btl_prepare_dst;
      mca_btl_base_module_send_fn_t           btl_send;
      mca_btl_base_module_sendi_fn_t          btl_sendi;
      mca_btl_base_module_put_fn_t            btl_put;
      mca_btl_base_module_get_fn_t            btl_get;
      mca_btl_base_module_dump_fn_t           btl_dump; 
     
      /** the mpool associated with this btl (optional) */ 
      mca_mpool_base_module_t*             btl_mpool; 
      /** register a default error handler */ 
      mca_btl_base_module_register_error_fn_t btl_register_error;
      /** fault tolerant even notification */
      mca_btl_base_module_ft_event_fn_t btl_ft_event;
  };
  typedef struct mca_btl_base_module_t mca_btl_base_module_t;
  
  /*
   * Macro for use in modules that are of type btl v2.0.1
   */
  #define MCA_BTL_BASE_VERSION_2_0_0 \
    MCA_BASE_VERSION_2_0_0, \
    "btl", 2, 0, 0
  
  END_C_DECLS
  
  #endif /* OMPI_MCA_BTL_H */
  