NAME

       AF_SMC - Sockets for SMC communication

SYNOPSIS

       #include <sys/socket.h>

       #define AF_SMC 43

       #define SMCPROTO_SMC  0

       #define SMCPROTO_SMC6 1

       tcp_sockfd = socket(AF_SMC, SOCK_STREAM, SMCPROTO_SMC);

       tcp_sockfd = socket(AF_SMC, SOCK_STREAM, SMCPROTO_SMC6);

DESCRIPTION

       Shared  Memory  Communication  via  RDMA  (SMC)  is  a  socket over the RDMA communication
       protocol that allows existing TCP socket applications to transparently benefit  from  RDMA
       when  exchanging  data over an RDMA over Converged Ethernet (RoCE) network. Those networks
       are not routable.  SMC provides host-to-host  direct  memory  access  without  traditional
       TCP/IP  processing  overhead.   SMC  offers  preservation  of  existing IP topology and IP
       security, and introduces minimal administrative and operational changes.  The exploitation
       of SMC is transparent to TCP socket applications.

       The  new  address  family AF_SMC supports the SMC protocol on Linux.  It keeps the address
       format of AF_INET and AF_INET6 sockets and supports streaming socket types only.

   Usage modes
       Two usage modes are possible:

       AF_SMC native usage
              uses  the  socket  domain  AF_SMC  instead  of  AF_INET  and   AF_INET6.    Specify
              SMCPROTO_SMC  for  AF_INET  compatible  socket  semantics,  and  SMC_PROTO_SMC6 for
              AF_INET6 respectively.

       Usage of AF_INET socket applications with SMC preload library
              converts AF_INET and AF_INET6 sockets to AF_SMC sockets.  The SMC  preload  library
              is part of the SMC tools package.

       SMC  socket  capabilities  are  negotiated  at  connection  setup.  If one peer is not SMC
       capable, further socket processing falls back to TCP usage automatically.

   Implementation details: Links and Link Groups
       To run RDMA traffic to a peer, a so-called link is established between a local  RoCE  card
       and  a  remote  RoCE card. To enhance availability, you can configure alternate links with
       automatic fail over.  Primary and backup links to a certain peer are  combined  in  a  so-
       called link group.

   RoCE adapter mapping: Creation of a pnet table
       The  SMC  protocol requires grouping of multiple physical networks - standard Ethernet and
       RoCE networks. Such groups are called Physical Networks (PNets).  For  SMC,  RoCE  adapter
       mapping  is configured within a table called pnet table.  Any available Ethernet interface
       can be combined with available RDMA-capable  network  interface  cards  (RNICs),  if  they
       belong to the same Converged Ethernet fabric.  To configure RoCE Adapter mapping, you must
       create a pnet table.  Modify the table with the smc-tools command smc_pnet.

       For details see smc_pnet(8).

   Displaying SMC socket state information
       SMC socket state information can be  obtained  with  the  smc-tools  command  smcss.   For
       details see smcss(8).

   Starting a TCP application to work with SMC
       To use an existing TCP application to work with SMC, use the SMC preload library.  The SMC
       Tools package provides the command smc_run to convert AF_INET and AF_INET6 socket calls to
       AF_SMC  socket  calls  by  means of the preload technique.  For more information about the
       preload mechanism, see also ld.so(8).

       Example:

              smc_run ftp

       This command-line example starts an FTP client over SMC.

   MTU and Infiniband data transfer
       Infiniband traffic may use MTU values 256, 512, 1024, 2048, or 4096.  SMC  determines  the
       configured  MTU size of the RoCE Ethernet port, announces this MTU size to the peer during
       connection start, and chooses the minimum MTU size of both peers.

SEE ALSO

       socket(2), ip(7), tcp(7), socket(7), smc_chk(8) smc_run(8), smcss(8), smc_pnet(8)

HISTORY

       AF_SMC, version 1.0.0

             Initial version.