RDMA_CM(7) Librdmacm Programmer's Manual RDMA_CM(7)NAMErdma_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, con‐
nected and unreliable datagram data transfers. It provides an RDMA
transport neutral interface for establishing connections. The API con‐
cepts 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 (con‐
nection setup / teardown) portions of an RDMA API, or only the communi‐
cation 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 pro‐
vided, an rdma_cm identifier will report its event data (results of
connecting, for example), on that channel. If a channel is not pro‐
vided, 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 communication. This flow assume asynchro‐
nous 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 applica‐
tions 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 communication. 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 function operates asynchronously, a
return value of 0 means that the operation was successfully started.
The operation 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 fail‐
ure.
Prior versions of the library would return -errno and not set errno for
some cases related to ENOMEM, ENODEV, ENODATA, EINVAL, and EADDRNO‐
TAVAIL codes. Applications that want to check these codes and have com‐
patability with prior library versions must manually set errno to the
negative of the return code if it is < -1.
SEE ALSOrdma_accept(3), rdma_ack_cm_event(3), rdma_bind_addr(3), rdma_con‐
nect(3), rdma_create_ep(3), rdma_create_event_channel(3), rdma_cre‐
ate_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)
