Eric,
understood, would it be acceptable if the SMC-specific hooks in the
TCP-code are enclosed with "#ifdef CONFIG_SMC ... #endif"?
Regards, Ursula
On Mon, 2015-07-06 at 18:08 +0200, Eric Dumazet wrote:
> On Mon, 2015-07-06 at 17:11 +0200, Ursula Braun wrote:
> > From: Ursula Braun <ursula.br...@de.ibm.com>
> >
> > The SMC-R protocol defines dynamic discovery of peers. This is done by
> > implementing experimental TCP options as defined in RFC6994. The TCP code
> > needs to be extended to support RFC6994.
> >
> > Setting the TCP experimental option for SMC-R [2] will be triggered from
> > kernel exploiters like the new SMC-R socket family by setting a new
> > flag "syn_smc" on struct tcp_sock of the connecting and the listening
> > socket. If the client peer is SMC-R capable, flag syn_smc is kept on the
> > connecting socket after the 3-way TCP handshake, otherwise it is reset.
> > If the server peer is SMC-R capable, the new connected TCP socket has
> > the new flag set, otherwise not.
> >
> > Code snippet client:
> > tcp_sk(sock->sk)->syn_smc = 1;
> > rc = kernel_connect(sock, addr, alen, flags);
> > if (tcp_sk(sock->sk)->syn_smc) {
> > /* switch to smc for this connection */
> >
> > Code snippet server:
> > tcp_sk(sock->sk)->syn_smc = 1;
> > rc = kernel_listen(sock, backlog);
> > rc = kernel_accept(sock, &newsock, 0);
> > if (tcp_sk(newsock->sk)->syn_smc) {
> > /* switch to smc for this connection */
> >
> > References:
> > [1] Shared Use of TCP Experimental Options RFC 6994:
> > https://tools.ietf.org/rfc/rfc6994.txt
> > [2] IANA ExID SMCR:
> >
> > http://www.iana.org/assignments/tcp-parameters/tcp-parameters.xhtml#tcp-exids
> >
> > This patch has already been posted in June 2013, but Dave Miller has
> > postponed applying till the user of the new flags, ie. the entire SMC-R
> > protocol stack is implemented.
> >
> > Signed-off-by: Ursula Braun <ubr...@linux.vnet.ibm.com>
>
>
> > struct tcp_out_options {
> > u16 options; /* bit field of OPTION_* */
> > @@ -544,6 +545,14 @@ static void tcp_options_write(__be32 *ptr, struct
> > tcp_sock *tp,
> > }
> > ptr += (len + 3) >> 2;
> > }
> > +
> > + if (unlikely(OPTION_SMC & options)) {
> > + *ptr++ = htonl((TCPOPT_NOP << 24) |
> > + (TCPOPT_NOP << 16) |
> > + (TCPOPT_EXP << 8) |
> > + (TCPOLEN_EXP_SMC_BASE));
> > + *ptr++ = htonl(TCPOPT_SMC_MAGIC);
> > + }
> > }
>
>
> I am concerned about adding an additional conditional branch in TCP
> write fast path, on all hosts, while SMC seems to be available only for
> some hardware class.
>
>
>
>
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