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.

smc-tools                                         January 2017                                         AF_SMC(7)