[RFC PATCH 5/5] sockets: Support multipath TCP

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Multipath TCP allows combining multiple interfaces/routes into a single
socket, with very little work for the user/admin.

It's enabled by 'mptcp' on most socket addresses:

   ./qemu-system-x86_64 -nographic -incoming tcp:0:4444,mptcp

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 io/dns-resolver.c   |  2 ++
 qapi/sockets.json   |  5 ++++-
 util/qemu-sockets.c | 34 ++++++++++++++++++++++++++++++++++
 3 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/io/dns-resolver.c b/io/dns-resolver.c
index 743a0efc87..b081e098bb 100644
--- a/io/dns-resolver.c
+++ b/io/dns-resolver.c
@@ -122,6 +122,8 @@ static int qio_dns_resolver_lookup_sync_inet(QIODNSResolver *resolver,
             .ipv4 = iaddr->ipv4,
             .has_ipv6 = iaddr->has_ipv6,
             .ipv6 = iaddr->ipv6,
+            .has_mptcp = iaddr->has_mptcp,
+            .mptcp = iaddr->mptcp,
         };
 
         (*addrs)[i] = newaddr;
diff --git a/qapi/sockets.json b/qapi/sockets.json
index 2e83452797..43122a38bf 100644
--- a/qapi/sockets.json
+++ b/qapi/sockets.json
@@ -57,6 +57,8 @@
 # @keep-alive: enable keep-alive when connecting to this socket. Not supported
 #              for passive sockets. (Since 4.2)
 #
+# @mptcp: enable multi-path TCP. (Since 6.0)
+#
 # Since: 1.3
 ##
 { 'struct': 'InetSocketAddress',
@@ -66,7 +68,8 @@
     '*to': 'uint16',
     '*ipv4': 'bool',
     '*ipv6': 'bool',
-    '*keep-alive': 'bool' } }
+    '*keep-alive': 'bool',
+    '*mptcp': 'bool' } }
 
 ##
 # @UnixSocketAddress:
diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c
index 8af0278f15..72527972d5 100644
--- a/util/qemu-sockets.c
+++ b/util/qemu-sockets.c
@@ -206,6 +206,21 @@ static int try_bind(int socket, InetSocketAddress *saddr, struct addrinfo *e)
 #endif
 }
 
+static int check_mptcp(const InetSocketAddress *saddr, struct addrinfo *ai,
+                       Error **errp)
+{
+    if (saddr->has_mptcp && saddr->mptcp) {
+#ifdef IPPROTO_MPTCP
+        ai->ai_protocol = IPPROTO_MPTCP;
+#else
+        error_setg(errp, "MPTCP unavailable in this build");
+        return -1;
+#endif
+    }
+
+    return 0;
+}
+
 static int inet_listen_saddr(InetSocketAddress *saddr,
                              int port_offset,
                              int num,
@@ -278,6 +293,11 @@ static int inet_listen_saddr(InetSocketAddress *saddr,
 
     /* create socket + bind/listen */
     for (e = res; e != NULL; e = e->ai_next) {
+        if (check_mptcp(saddr, e, &err)) {
+            error_propagate(errp, err);
+            return -1;
+        }
+
         getnameinfo((struct sockaddr*)e->ai_addr,e->ai_addrlen,
                         uaddr,INET6_ADDRSTRLEN,uport,32,
                         NI_NUMERICHOST | NI_NUMERICSERV);
@@ -456,6 +476,11 @@ int inet_connect_saddr(InetSocketAddress *saddr, Error **errp)
     for (e = res; e != NULL; e = e->ai_next) {
         error_free(local_err);
         local_err = NULL;
+
+        if (check_mptcp(saddr, e, &local_err)) {
+            break;
+        }
+
         sock = inet_connect_addr(saddr, e, &local_err);
         if (sock >= 0) {
             break;
@@ -687,6 +712,15 @@ int inet_parse(InetSocketAddress *addr, const char *str, Error **errp)
         }
         addr->has_keep_alive = true;
     }
+    begin = strstr(optstr, ",mptcp");
+    if (begin) {
+        if (inet_parse_flag("mptcp", begin + strlen(",mptcp"),
+                            &addr->mptcp, errp) < 0)
+        {
+            return -1;
+        }
+        addr->has_mptcp = true;
+    }
     return 0;
 }
 
-- 
2.31.1