# rdma_connect

## NAME



           rdma_connect - Initiate an active connection request.
    


## SYNOPSIS



           **#include <rdma/rdma_cma.h>**
    
           **int rdma_connect (struct rdma_cm_id ***_id_**, struct rdma_conn_param**
           *****_conn_param_**);**
    


## ARGUMENTS



           id          RDMA identifier.
    
           conn_param  connection parameters.  See CONNECTION PROPERTIES
                       below for details.
    


## DESCRIPTION



           For an rdma_cm_id of type RDMA_PS_TCP, this call initiates a
           connection request to a remote destination.  For an rdma_cm_id of
           type RDMA_PS_UDP, it initiates a lookup of the remote QP providing
           the datagram service.
    


## RETURN VALUE



           Returns 0 on success, or -1 on error.  If an error occurs, errno
           will be set to indicate the failure reason.
    


## NOTES



           Users must have resolved a route to the destination address by
           having called rdma_resolve_route or rdma_create_ep before calling
           this routine.
    


## CONNECTION PROPERTIES



           The following properties are used to configure the communication
           and specified by the conn_param parameter when connecting or
           establishing datagram communication.
    
           private_data
                  References a user-controlled data buffer.  The contents of
                  the buffer are copied and transparently passed to the
                  remote side as part of the communication request.  May be
                  NULL if private_data is not required.
    
           private_data_len
                  Specifies the size of the user-controlled data buffer.
                  Note that the actual amount of data transferred to the
                  remote side is transport dependent and may be larger than
                  that requested.
    
           responder_resources
                  The maximum number of outstanding RDMA read and atomic
                  operations that the local side will accept from the remote
                  side.  Applies only to RDMA_PS_TCP.  This value must be
                  less than or equal to the local RDMA device attribute
                  max_qp_rd_atom and remote RDMA device attribute
                  max_qp_init_rd_atom.  The remote endpoint can adjust this
                  value when accepting the connection.
    
           initiator_depth
                  The maximum number of outstanding RDMA read and atomic
                  operations that the local side will have to the remote
                  side.  Applies only to RDMA_PS_TCP.  This value must be
                  less than or equal to the local RDMA device attribute
                  max_qp_init_rd_atom and remote RDMA device attribute
                  max_qp_rd_atom.  The remote endpoint can adjust this value
                  when accepting the connection.
    
           flow_control
                  Specifies if hardware flow control is available.  This
                  value is exchanged with the remote peer and is not used to
                  configure the QP.  Applies only to RDMA_PS_TCP.
    
           retry_count
                  The maximum number of times that a data transfer operation
                  should be retried on the connection when an error occurs.
                  This setting controls the number of times to retry send,
                  RDMA, and atomic operations when timeouts occur.  Applies
                  only to RDMA_PS_TCP.
    
           rnr_retry_count
                  The maximum number of times that a send operation from the
                  remote peer should be retried on a connection after
                  receiving a receiver not ready (RNR) error.  RNR errors are
                  generated when a send request arrives before a buffer has
                  been posted to receive the incoming data.  Applies only to
                  RDMA_PS_TCP.
    
           srq    Specifies if the QP associated with the connection is using
                  a shared receive queue.  This field is ignored by the
                  library if a QP has been created on the rdma_cm_id.
                  Applies only to RDMA_PS_TCP.
    
           qp_num Specifies the QP number associated with the connection.
                  This field is ignored by the library if a QP has been
                  created on the rdma_cm_id.  Applies only to RDMA_PS_TCP.
    


## INFINIBAND SPECIFIC



           In addition to the connection properties defined above, InfiniBand
           QPs are configured with minimum RNR NAK timer and local ACK
           timeout values.  The minimum RNR NAK timer value is set to 0, for
           a delay of 655 ms.  The local ACK timeout is calculated based on
           the packet lifetime and local HCA ACK delay.  The packet lifetime
           is determined by the InfiniBand Subnet Administrator and is part
           of the resolved route (path record) information.  The HCA ACK
           delay is a property of the locally used HCA.
    
           Retry count and RNR retry count values are 3-bit values.
    
           The length of the private data provided by the user is limited to
           56 bytes for RDMA_PS_TCP, or 180 bytes for RDMA_PS_UDP.
    


## IWARP SPECIFIC



           Connections established over iWarp RDMA devices currently require
           that the active side of the connection send the first message.
    


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