# rdma_accept

## NAME



           rdma_accept - Called to accept a connection request.
    


## SYNOPSIS



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


## ARGUMENTS



           id          Connection identifier associated with the request.
    
           conn_param  Information needed to establish the connection.  See
                       CONNECTION PROPERTIES below for details.
    


## DESCRIPTION



           Called from the listening side to accept a connection or datagram
           service lookup request.
    


## RETURN VALUE



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


## NOTES



           Unlike the socket accept routine, rdma_accept is not called on a
           listening rdma_cm_id.  Instead, after calling rdma_listen, the
           user waits for an RDMA_CM_EVENT_CONNECT_REQUEST event to occur.
           Connection request events give the user a newly created
           rdma_cm_id, similar to a new socket, but the rdma_cm_id is bound
           to a specific RDMA device.  rdma_accept is called on the new
           rdma_cm_id.
    


## CONNECTION PROPERTIES



           The following properties are used to configure the communication
           and specified by the conn_param parameter when accepting a
           connection or datagram communication request.  Users should use
           the rdma_conn_param values reported in the connection request
           event to determine appropriate values for these fields when
           accepting.  Users may reference the rdma_conn_param structure in
           the connection event directly, or can reference their own
           structure.  If the rdma_conn_param structure from an event is
           referenced, the event must not be acked until after this call
           returns.
    
           If the conn_param parameter is NULL, the values reported in the
           connection request event are used, adjusted down based on local
           hardware restrictions.
    
           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, but preferably greater than or equal to the
                  responder_resources value reported in the connect request
                  event.
    
           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 the initiator_depth value reported
                  in the connect request event.
    
           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
                  This value is ignored.
    
           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.
    


## 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 route (path record) information obtained by the active side
           of the connection.  The HCA ACK delay is a property of the locally
           used HCA.
    
           The RNR retry count is a 3-bit value.
    
           The length of the private data provided by the user is limited to
           196 bytes for RDMA_PS_TCP, or 136 bytes for RDMA_PS_UDP.
    


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