Ubuntu Manpage: rdma_connect - Initiate an active connection request.

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.