util/qemu-sockets: Introduce inet socket options controlling TCP keep-alive

With the default TCP stack configuration, it could be even 2 hours
before the connection times out due to the other side not being
reachable. However, in some cases, the application needs to be aware of
a connection issue much sooner.

This is the case, for example, for postcopy live migration. If there is
no traffic from the migration destination guest (server-side) to the
migration source guest (client-side), the destination keeps waiting for
pages indefinitely and does not switch to the postcopy-paused state.
This can happen, for example, if the destination QEMU instance is
started with the '-S' command line option and the machine is not started
yet, or if the machine is idle and produces no new page faults for
not-yet-migrated pages.

This patch introduces new inet socket parameters that control count,
idle period, and interval of TCP keep-alive packets before the
connection is considered broken. These parameters are available on
systems where the respective TCP socket options are defined, that
includes Linux, Windows, macOS, but not OpenBSD. Additionally, macOS
defines TCP_KEEPIDLE as TCP_KEEPALIVE instead, so the patch supplies its
own definition.

The default value for all is 0, which means the system configuration is
used.

Signed-off-by: Juraj Marcin <jmarcin@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

1 files changed, 80 insertions, 0 deletions

diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c
index 403dc26b36..4773755fd5 100644
--- a/util/qemu-sockets.c
+++ b/util/qemu-sockets.c
@@ -45,6 +45,14 @@
 # define AI_NUMERICSERV 0
 #endif
 
+/*
+ * On macOS TCP_KEEPIDLE is available under a different name, TCP_KEEPALIVE.
+ * https://github.com/apple/darwin-xnu/blob/xnu-4570.1.46/bsd/man/man4/tcp.4#L172
+ */
+#if defined(TCP_KEEPALIVE) && !defined(TCP_KEEPIDLE)
+# define TCP_KEEPIDLE TCP_KEEPALIVE
+#endif
+
 
 static int inet_getport(struct addrinfo *e)
 {
@@ -218,6 +226,42 @@ static int inet_set_sockopts(int sock, InetSocketAddress *saddr, Error **errp)
                              "Unable to set keep-alive option on socket");
             return -1;
         }
+#ifdef HAVE_TCP_KEEPCNT
+        if (saddr->has_keep_alive_count && saddr->keep_alive_count) {
+            int keep_count = saddr->keep_alive_count;
+            ret = setsockopt(sock, IPPROTO_TCP, TCP_KEEPCNT, &keep_count,
+                             sizeof(keep_count));
+            if (ret < 0) {
+                error_setg_errno(errp, errno,
+                                 "Unable to set TCP keep-alive count option on socket");
+                return -1;
+            }
+        }
+#endif
+#ifdef HAVE_TCP_KEEPIDLE
+        if (saddr->has_keep_alive_idle && saddr->keep_alive_idle) {
+            int keep_idle = saddr->keep_alive_idle;
+            ret = setsockopt(sock, IPPROTO_TCP, TCP_KEEPIDLE, &keep_idle,
+                             sizeof(keep_idle));
+            if (ret < 0) {
+                error_setg_errno(errp, errno,
+                                 "Unable to set TCP keep-alive idle option on socket");
+                return -1;
+            }
+        }
+#endif
+#ifdef HAVE_TCP_KEEPINTVL
+        if (saddr->has_keep_alive_interval && saddr->keep_alive_interval) {
+            int keep_interval = saddr->keep_alive_interval;
+            ret = setsockopt(sock, IPPROTO_TCP, TCP_KEEPINTVL, &keep_interval,
+                             sizeof(keep_interval));
+            if (ret < 0) {
+                error_setg_errno(errp, errno,
+                                 "Unable to set TCP keep-alive interval option on socket");
+                return -1;
+            }
+        }
+#endif
     }
     return 0;
 }
@@ -630,6 +674,24 @@ static QemuOptsList inet_opts = {
             .name = "keep-alive",
             .type = QEMU_OPT_BOOL,
         },
+#ifdef HAVE_TCP_KEEPCNT
+        {
+            .name = "keep-alive-count",
+            .type = QEMU_OPT_NUMBER,
+        },
+#endif
+#ifdef HAVE_TCP_KEEPIDLE
+        {
+            .name = "keep-alive-idle",
+            .type = QEMU_OPT_NUMBER,
+        },
+#endif
+#ifdef HAVE_TCP_KEEPINTVL
+        {
+            .name = "keep-alive-interval",
+            .type = QEMU_OPT_NUMBER,
+        },
+#endif
 #ifdef HAVE_IPPROTO_MPTCP
         {
             .name = "mptcp",
@@ -695,6 +757,24 @@ int inet_parse(InetSocketAddress *addr, const char *str, Error **errp)
         addr->has_keep_alive = true;
         addr->keep_alive = qemu_opt_get_bool(opts, "keep-alive", false);
     }
+#ifdef HAVE_TCP_KEEPCNT
+    if (qemu_opt_find(opts, "keep-alive-count")) {
+        addr->has_keep_alive_count = true;
+        addr->keep_alive_count = qemu_opt_get_number(opts, "keep-alive-count", 0);
+    }
+#endif
+#ifdef HAVE_TCP_KEEPIDLE
+    if (qemu_opt_find(opts, "keep-alive-idle")) {
+        addr->has_keep_alive_idle = true;
+        addr->keep_alive_idle = qemu_opt_get_number(opts, "keep-alive-idle", 0);
+    }
+#endif
+#ifdef HAVE_TCP_KEEPINTVL
+    if (qemu_opt_find(opts, "keep-alive-interval")) {
+        addr->has_keep_alive_interval = true;
+        addr->keep_alive_interval = qemu_opt_get_number(opts, "keep-alive-interval", 0);
+    }
+#endif
 #ifdef HAVE_IPPROTO_MPTCP
     if (qemu_opt_find(opts, "mptcp")) {
         addr->has_mptcp = true;