Re: [PATCH v4] sctp: Implement quick failover draft from tsvwg

On Fri, Jul 20, 2012 at 01:55:35PM -0400, Vlad Yasevich wrote:

On 07/20/2012 01:19 PM, Neil Horman wrote:

quoted

I've seen several attempts recently made to do quick failover of sctp transports
by reducing various retransmit timers and counters.  While its possible to
implement a faster failover on multihomed sctp associations, its not
particularly robust, in that it can lead to unneeded retransmits, as well as
false connection failures due to intermittent latency on a network.

Instead, lets implement the new ietf quick failover draft found here:
http://tools.ietf.org/html/draft-nishida-tsvwg-sctp-failover-05

This will let the sctp stack identify transports that have had a small number of
errors, and avoid using them quickly until their reliability can be
re-established.  I've tested this out on two virt guests connected via multiple
isolated virt networks and believe its in compliance with the above draft and
works well.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Vlad Yasevich <redacted>
CC: Sridhar Samudrala <redacted>
CC: "David S. Miller" <davem@davemloft.net>
CC: linux-sctp@vger.kernel.org
CC: joe@perches.com

---
Change notes:

V2)
- Added socket option API from section 6.1 of the specification, as per
request from Vlad. Adding this socket option allows us to alter both the path
maximum retransmit value and the path partial failure threshold for each
transport and the association as a whole.

- Added a per transport pf_retrans value, and initialized it from the
association value.  This makes each transport independently configurable as per
the socket option above, and prevents changes in the sysctl from bleeding into
an already created association.

V3)
- Cleaned up some line spacing (Joe Perches)
- Fixed some socket option user data sanitization (Vlad Yasevich)

V4)
- Added additional documentation (Flavio Leitner)
---
 Documentation/networking/ip-sysctl.txt |   14 +++++
 include/net/sctp/constants.h           |    1 +
 include/net/sctp/structs.h             |   20 ++++++-
 include/net/sctp/user.h                |   11 ++++
 net/sctp/associola.c                   |   37 ++++++++++--
 net/sctp/outqueue.c                    |    6 +-
 net/sctp/sm_sideeffect.c               |   33 +++++++++-
 net/sctp/socket.c                      |  100 ++++++++++++++++++++++++++++++++
 net/sctp/sysctl.c                      |    9 +++
 net/sctp/transport.c                   |    4 +-
 10 files changed, 220 insertions(+), 15 deletions(-)

[ snip ]

quoted

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index b3b8a8d..fef9bfa 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c

@@ -3470,6 +3470,56 @@ static int sctp_setsockopt_auto_asconf(struct sock *sk, char __user *optval,
 }


+/*
+ * SCTP_PEER_ADDR_THLDS
+ *
+ * This option allows us to alter the partially failed threshold for one or all
+ * transports in an association.  See Section 6.1 of:
+ * http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt
+ */
+static int sctp_setsockopt_paddr_thresholds(struct sock *sk,
+					    char __user *optval,
+					    unsigned int optlen)
+{
+	struct sctp_paddrthlds val;
+	struct sctp_transport *trans;
+	struct sctp_association *asoc;
+
+	if (optlen < sizeof(struct sctp_paddrthlds))
+		return -EINVAL;
+	if (copy_from_user(&val, (struct sctp_paddrthlds __user *)optval,
+			   sizeof(struct sctp_paddrthlds)))
+		return -EFAULT;
+
+	/* path_max_retrans shouldn't ever be zero */
+	if (!val.spt_pathmaxrxt)
+		return -EINVAL;

I am not sure I like this solution.  This means that the application
must fetch the pathmaxrx and then write the same value back here.
Why not simply ignore the patthmaxrxt if it's 0?  That way someone
can just tweak the pf value without changing the pathmaxrxt.

Yeah, I can make that change.
Neil