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Message-ID: <1370420173.11064.15.camel@BR9GV9YG.de.ibm.com>
Date: Wed, 05 Jun 2013 10:16:13 +0200
From: Ursula Braun <ubraun@...ux.vnet.ibm.com>
To: netdev@...r.kernel.org
Cc: ursula.braun@...ibm.com
Subject: [RFC patch net-next 1/1] tcp: introduce TCP experimental option for
SMC-R
From: Ursula Braun <ubraun@...ux.vnet.ibm.com>
RDMA is considered to become an important technology for IBM System z
(which is "s390" in Linux kernel terminology).
We intend to introduce a new socket protocol family providing Shared
Memory Communications over RDMA called SMC-R. The respective IETF draft
can be found at [1]. Its objective is to come up with a low latency, but
also low CPU cost communication vehicle exploiting RDMA technology
transparently while keeping the TCP/IP administration model and allowing
fallback to TCP sockets if necessary. The SMC-R protocol makes use of
the existing TCP 3-way hand shake, the TCP connection and IP topology to
preserve the traditional network administrative model including network
security. The SMC-R protocol also enables redundancy and load balancing
across multiple RDMA-capable devices.
An essential part of this approach is the so-called "rendezvous"
protocol through TCP sockets. It is used to dynamically discover RDMA
capabilities of connection partners and exchange credentials necessary
to exploit that capability if present and to have a fallback to TCP
sockets otherwise. It makes use of the concept of TCP experimental
options as described in [2].
This is the only part of our approach touching common TCP code in the
Linux kernel.
According to the SMC-R protocol connections are set up using regular
TCP sockets. During the TCP 3-way handshake, a new experimental TCP
option announces SMC-R capability. If both partners indicate SMC-R
capability then at the completion of the 3-way TCP handshake the SMC-R
layers in each peer take control of the TCP connection.
An implementation of a new TCP experimental option requires changes to
the existing TCP kernel code. This RFC describes our intended changes to
support TCP experimental option SMC-R. I would like to receive feedback
- if the proposed implementation of using the RFC'ed TCP experimental
option is considered done at the right level by the Linux kernel
community.
- and if not so, how the RFC can be implemented otherwise more
appropriately.
- if certain aspects prevent inclusion into the Linux kernel.
Setting TCP experimental option SMC-R will be triggered from kernel
exploiters like our new SMC-R socket address 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 TPC 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] https://datatracker.ietf.org/doc/draft-fox-tcpm-shared-memory-rdma/
[2] http://tools.ietf.org/html/draft-ietf-tcpm-experimental-options-05
Signed-off-by: Ursula Braun <ubraun@...ux.vnet.ibm.com>
---
include/linux/tcp.h | 4 +++-
include/net/request_sock.h | 3 ++-
include/net/tcp.h | 3 +++
net/ipv4/tcp_input.c | 38
+++++++++++++++++++++++++-------------
net/ipv4/tcp_ipv4.c | 3 +++
net/ipv4/tcp_minisocks.c | 4 ++++
net/ipv4/tcp_output.c | 26 ++++++++++++++++++++++++++
7 files changed, 66 insertions(+), 15 deletions(-)
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -90,6 +90,7 @@ struct tcp_options_received {
sack_ok : 4, /* SACK seen on SYN packet */
snd_wscale : 4, /* Window scaling received from sender */
rcv_wscale : 4; /* Window scaling to send to receiver */
+ u8 smc_capability:1; /* SMC capability >------->-------*/
u8 num_sacks; /* Number of SACK blocks */
u16 user_mss; /* mss requested by user in ioctl */
u16 mss_clamp; /* Maximal mss, negotiated at connection setup */
@@ -198,7 +199,8 @@ struct tcp_sock {
u8 do_early_retrans:1,/* Enable RFC5827 early-retransmit */
syn_data:1, /* SYN includes data */
syn_fastopen:1, /* SYN includes Fast Open option */
- syn_data_acked:1;/* data in SYN is acked by SYN-ACK */
+ syn_data_acked:1,/* data in SYN is acked by SYN-ACK */
+ syn_smc:1; /* SYN includes SMC>---->------->-------*/
u32 tlp_high_seq; /* snd_nxt at the time of TLP retransmit. */
/* RTT measurement */
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -51,7 +51,8 @@ struct request_sock {
struct request_sock *dl_next;
u16 mss;
u8 num_retrans; /* number of retransmits */
- u8 cookie_ts:1; /* syncookie: encode tcpopts in timestamp */
+ u8 cookie_ts:1, /* syncookie: encode tcpopts in timestamp */
+ smc_capability:1;
u8 num_timeout:7; /* number of timeouts */
/* The following two fields can be easily recomputed I think -AK */
u32 window_clamp; /* window clamp at creation time */
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -184,6 +184,7 @@ extern void tcp_time_wait(struct sock *s
* experimental options. See
draft-ietf-tcpm-experimental-options-00.txt
*/
#define TCPOPT_FASTOPEN_MAGIC 0xF989
+#define TCPOPT_SMC_MAGIC 0xE2D4C3D9
/*
* TCP option lengths
@@ -199,6 +200,7 @@ extern void tcp_time_wait(struct sock *s
#define TCPOLEN_COOKIE_PAIR 3 /* Cookie pair header extension */
#define TCPOLEN_COOKIE_MIN (TCPOLEN_COOKIE_BASE+TCP_COOKIE_MIN)
#define TCPOLEN_COOKIE_MAX (TCPOLEN_COOKIE_BASE+TCP_COOKIE_MAX)
+#define TCPOLEN_EXP_SMC_BASE 6
/* But this is what stacks really send out. */
#define TCPOLEN_TSTAMP_ALIGNED 12
@@ -209,6 +211,7 @@ extern void tcp_time_wait(struct sock *s
#define TCPOLEN_SACK_PERBLOCK 8
#define TCPOLEN_MD5SIG_ALIGNED 20
#define TCPOLEN_MSS_ALIGNED 4
+#define TCPOLEN_EXP_SMC_BASE_ALIGNED 8
/* Flags in tp->nonagle */
#define TCP_NAGLE_OFF 1 /* Nagle's algo is disabled */
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3510,20 +3510,29 @@ void tcp_parse_options(const struct sk_b
break;
#endif
case TCPOPT_EXP:
- /* Fast Open option shares code 254 using a
- * 16 bits magic number. It's valid only in
- * SYN or SYN-ACK with an even size.
- */
- if (opsize < TCPOLEN_EXP_FASTOPEN_BASE ||
- get_unaligned_be16(ptr) != TCPOPT_FASTOPEN_MAGIC ||
- foc == NULL || !th->syn || (opsize & 1))
+ if (!th->syn || (opsize & 1) ||
+ (opsize < TCPOLEN_EXP_FASTOPEN_BASE))
+ break;
+ if (get_unaligned_be16(ptr) == TCPOPT_FASTOPEN_MAGIC) {
+ if (foc == NULL)
+ break;
+ /* Fast Open option shares code 254 using a
+ * 16 bits magic number. It's valid only in
+ * SYN or SYN-ACK with an even size.
+ */
+ foc->len = opsize - TCPOLEN_EXP_FASTOPEN_BASE;
+ if (foc->len >= TCP_FASTOPEN_COOKIE_MIN &&
+ foc->len <= TCP_FASTOPEN_COOKIE_MAX)
+ memcpy(foc->val, ptr + 2, foc->len);
+ else if (foc->len != 0)
+ foc->len = -1;
+ break;
+ } else if (opsize < TCPOLEN_EXP_SMC_BASE)
break;
- foc->len = opsize - TCPOLEN_EXP_FASTOPEN_BASE;
- if (foc->len >= TCP_FASTOPEN_COOKIE_MIN &&
- foc->len <= TCP_FASTOPEN_COOKIE_MAX)
- memcpy(foc->val, ptr + 2, foc->len);
- else if (foc->len != 0)
- foc->len = -1;
+ else if (get_unaligned_be32(ptr) == TCPOPT_SMC_MAGIC) {
+ opt_rx->smc_capability = 1;
+ break;
+ }
break;
}
@@ -5418,6 +5427,9 @@ static int tcp_rcv_synsent_state_process
* is initialized. */
tp->copied_seq = tp->rcv_nxt;
+ if (tp->syn_smc && !tp->rx_opt.smc_capability)
+ tp->syn_smc = 0;
+
smp_mb();
tcp_finish_connect(sk, skb);
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1508,6 +1508,9 @@ int tcp_v4_conn_request(struct sock *sk,
tmp_opt.user_mss = tp->rx_opt.user_mss;
tcp_parse_options(skb, &tmp_opt, 0, want_cookie ? NULL : &foc);
+ if (tmp_opt.smc_capability)
+ req->smc_capability = 1;
+
if (want_cookie && !tmp_opt.saw_tstamp)
tcp_clear_options(&tmp_opt);
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -385,6 +385,10 @@ struct sock *tcp_create_openreq_child(st
struct tcp_request_sock *treq = tcp_rsk(req);
struct inet_connection_sock *newicsk = inet_csk(newsk);
struct tcp_sock *newtp = tcp_sk(newsk);
+ struct tcp_sock *oldtp = tcp_sk(sk);
+
+ if (oldtp->syn_smc && !req->smc_capability)
+ newtp->syn_smc = 0;
/* Now setup tcp_sock */
newtp->pred_flags = 0;
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -381,6 +381,7 @@ static inline bool tcp_urg_mode(const st
#define OPTION_MD5 (1 << 2)
#define OPTION_WSCALE (1 << 3)
#define OPTION_FAST_OPEN_COOKIE (1 << 8)
+#define OPTION_SMC (1 << 9)
struct tcp_out_options {
u16 options; /* bit field of OPTION_* */
@@ -490,6 +491,14 @@ static void tcp_options_write(__be32 *pt
}
ptr += (foc->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);
+ }
}
/* Compute TCP options for SYN packets. This is not the final
@@ -553,6 +562,14 @@ static unsigned int tcp_syn_options(stru
}
}
+ if (tp->syn_smc) {
+ int need = TCPOLEN_EXP_SMC_BASE_ALIGNED;
+ if (remaining >= need) {
+ opts->options |= OPTION_SMC;
+ remaining -= need;
+ }
+ }
+
return MAX_TCP_OPTION_SPACE - remaining;
}
@@ -565,6 +582,7 @@ static unsigned int tcp_synack_options(s
struct tcp_fastopen_cookie *foc)
{
struct inet_request_sock *ireq = inet_rsk(req);
+ struct tcp_sock *tp = tcp_sk(sk);
unsigned int remaining = MAX_TCP_OPTION_SPACE;
#ifdef CONFIG_TCP_MD5SIG
@@ -613,6 +631,14 @@ static unsigned int tcp_synack_options(s
remaining -= need;
}
}
+
+ if (tp->syn_smc && req->smc_capability) {
+ int need = TCPOLEN_EXP_SMC_BASE_ALIGNED;
+ if (remaining >= need) {
+ opts->options |= OPTION_SMC;
+ remaining -= need;
+ }
+ }
return MAX_TCP_OPTION_SPACE - remaining;
}
--
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