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RDMA_CM(7)               Librdmacm Programmer's Manual              RDMA_CM(7)



NAME
       rdma_cm - RDMA communication manager.

SYNOPSIS
       #include <rdma/rdma_cma.h>

DESCRIPTION
       Used to establish communication over RDMA transports.

NOTES
       The  RDMA  CM  is a communication manager used to setup reliable, connected and unreliable datagram data trans-
       fers.  It provides an RDMA transport neutral interface for establishing  connections.   The  API  concepts  are
       based  on  sockets, but adapted for queue pair (QP) based semantics: communication must be over a specific RDMA
       device, and data transfers are message based.

       The RDMA CM can control both the QP and communication management (connection setup / teardown) portions  of  an
       RDMA  API,  or  only the communication management piece.  It works in conjunction with the verbs API defined by
       the libibverbs library.  The libibverbs library provides the underlying interfaces needed to send  and  receive
       data.

       The  RDMA  CM  can  operate  asynchronously  or synchronously.  The mode of operation is controlled by the user
       through the use of the rdma_cm event channel parameter in specific calls.  If an event channel is provided,  an
       rdma_cm  identifier  will  report  its  event data (results of connecting, for example), on that channel.  If a
       channel is not provided, then all rdma_cm operations for the selected rdma_cm identifier will block until  they
       complete.

RDMA VERBS
       The rdma_cm supports the full range of verbs available through the libibverbs library and interfaces.  However,
       it also provides wrapper functions for some of the more commonly used verbs funcationality.  The  full  set  of
       abstracted verb calls are:

       rdma_reg_msgs  - register an array of buffers for sending and receiving

       rdma_reg_read  - registers a buffer for RDMA read operations

       rdma_reg_write - registers a buffer for RDMA write operations

       rdma_dereg_mr  - deregisters a memory region

       rdma_post_recv  - post a buffer to receive a message

       rdma_post_send  - post a buffer to send a message

       rdma_post_read  - post an RDMA to read data into a buffer

       rdma_post_write - post an RDMA to send data from a buffer

       rdma_post_recvv  - post a vector of buffers to receive a message

       rdma_post_sendv  - post a vector of buffers to send a message

       rdma_post_readv  - post a vector of buffers to receive an RDMA read

       rdma_post_writev - post a vector of buffers to send an RDMA write

       rdma_post_ud_send - post a buffer to send a message on a UD QP

       rdma_get_send_comp - get completion status for a send or RDMA operation

       rdma_get_recv_comp - get information about a completed receive

CLIENT OPERATION
       This  section  provides a general overview of the basic operation for the active, or client, side of communica-
       tion.  This flow assume asynchronous operation with low level call details shown.  For  synchronous  operation,
       calls  to rdma_create_event_channel, rdma_get_cm_event, rdma_ack_cm_event, and rdma_destroy_event_channel would
       be eliminated.  Abstracted calls, such as rdma_create_ep encapsulate serveral of these  calls  under  a  single
       API.  Users may also refer to the example applications for code samples.  A general connection flow would be:

       rdma_getaddrinfo
              retrieve address information of the destination

       rdma_create_event_channel
              create channel to receive events

       rdma_create_id
              allocate an rdma_cm_id, this is conceptually similar to a socket

       rdma_resolve_addr
              obtain a local RDMA device to reach the remote address

       rdma_get_cm_event
              wait for RDMA_CM_EVENT_ADDR_RESOLVED event

       rdma_ack_cm_event
              ack event

       rdma_create_qp
              allocate a QP for the communication

       rdma_resolve_route
              determine the route to the remote address

       rdma_get_cm_event
              wait for RDMA_CM_EVENT_ROUTE_RESOLVED event

       rdma_ack_cm_event
              ack event

       rdma_connect
              connect to the remote server

       rdma_get_cm_event
              wait for RDMA_CM_EVENT_ESTABLISHED event

       rdma_ack_cm_event
              ack event

       Perform data transfers over connection

       rdma_disconnect
              tear-down connection

       rdma_get_cm_event
              wait for RDMA_CM_EVENT_DISCONNECTED event

       rdma_ack_cm_event
              ack event

       rdma_destroy_qp
              destroy the QP

       rdma_destroy_id
              release the rdma_cm_id

       rdma_destroy_event_channel
              release the event channel

       An  almost  identical process is used to setup unreliable datagram (UD) communication between nodes.  No actual
       connection is formed between QPs however, so disconnection is not needed.

       Although this example shows the client initiating the disconnect, either side of a connection may initiate  the
       disconnect.

SERVER OPERATION
       This  section provides a general overview of the basic operation for the passive, or server, side of communica-
       tion.  A general connection flow would be:

       rdma_create_event_channel
              create channel to receive events

       rdma_create_id
              allocate an rdma_cm_id, this is conceptually similar to a socket

       rdma_bind_addr
              set the local port number to listen on

       rdma_listen
              begin listening for connection requests

       rdma_get_cm_event
              wait for RDMA_CM_EVENT_CONNECT_REQUEST event with a new rdma_cm_id

       rdma_create_qp
              allocate a QP for the communication on the new rdma_cm_id

       rdma_accept
              accept the connection request

       rdma_ack_cm_event
              ack event

       rdma_get_cm_event
              wait for RDMA_CM_EVENT_ESTABLISHED event

       rdma_ack_cm_event
              ack event

       Perform data transfers over connection

       rdma_get_cm_event
              wait for RDMA_CM_EVENT_DISCONNECTED event

       rdma_ack_cm_event
              ack event

       rdma_disconnect
              tear-down connection

       rdma_destroy_qp
              destroy the QP

       rdma_destroy_id
              release the connected rdma_cm_id

       rdma_destroy_id
              release the listening rdma_cm_id

       rdma_destroy_event_channel
              release the event channel

RETURN CODES
       =  0   success

       = -1   error - see errno for more details

       Most librdmacm functions return 0 to indicate success, and a -1 return value to indicate failure.  If  a  func-
       tion operates asynchronously, a return value of 0 means that the operation was successfully started.  The oper-
       ation could still complete in error; users should check the status of the related event.  If the  return  value
       is -1, then errno will contain additional information regarding the reason for the failure.

       Prior  versions  of the library would return -errno and not set errno for some cases related to ENOMEM, ENODEV,
       ENODATA, EINVAL, and EADDRNOTAVAIL codes. Applications that want to check these codes  and  have  compatability
       with prior library versions must manually set errno to the negative of the return code if it is < -1.

SEE ALSO
       rdma_accept(3),   rdma_ack_cm_event(3),   rdma_bind_addr(3),   rdma_connect(3),   rdma_create_ep(3),  rdma_cre-
       ate_event_channel(3),    rdma_create_id(3),    rdma_create_qp(3),     rdma_dereg_mr(3),     rdma_destroy_ep(3),
       rdma_destroy_event_channel(3),  rdma_destroy_id(3),  rdma_destroy_qp(3), rdma_disconnect(3), rdma_event_str(3),
       rdma_free_devices(3),  rdma_getaddrinfo(3),  rdma_get_cm_event(3),  rdma_get_devices(3),  rdma_get_dst_port(3),
       rdma_get_local_addr(3),        rdma_get_peer_addr(3),        rdma_get_recv_comp(3),        rdma_get_request(3),
       rdma_get_send_comp(3), rdma_get_src_port(3), rdma_join_multicast(3),  rdma_leave_multicast(3),  rdma_listen(3),
       rdma_migrate_id(3),      rdma_notify(3),      rdma_post_read(3)      rdma_post_readv(3),     rdma_post_recv(3),
       rdma_post_recvv(3),   rdma_post_send(3),    rdma_post_sendv(3),    rdma_post_ud_send(3),    rdma_post_write(3),
       rdma_post_writev(3),      rdma_reg_msgs(3),      rdma_reg_read(3),      rdma_reg_write(3),      rdma_reject(3),
       rdma_resolve_addr(3),  rdma_resolve_route(3),  rdma_set_option(3)  mckey(1),  rdma_client(1),   rdma_server(1),
       rping(1), ucmatose(1), udaddy(1)



librdmacm                         2010-07-19                        RDMA_CM(7)