The default idle period for TCP connection could be even 2 hours.
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 '-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 a new inet socket parameter on platforms where
TCP_KEEPIDLE is defined and passes the configured value to the
TCP_KEEPIDLE socket option when a client-side or server-side socket is
created.

The default value is 0, which means system configuration is used, and no
custom value is set.

Signed-off-by: Juraj Marcin <jmarcin@redhat.com>
---
 io/dns-resolver.c   |  4 ++++
 meson.build         |  2 ++
 qapi/sockets.json   |  5 +++++
 util/qemu-sockets.c | 39 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 50 insertions(+)

diff --git a/io/dns-resolver.c b/io/dns-resolver.c
index ee7403b65b..03c59673f0 100644
--- a/io/dns-resolver.c
+++ b/io/dns-resolver.c
@@ -128,6 +128,10 @@ static int qio_dns_resolver_lookup_sync_inet(QIODNSResolver *resolver,
 #endif
             .has_keep_alive = iaddr->has_keep_alive,
             .keep_alive = iaddr->keep_alive,
+#ifdef HAVE_TCP_KEEPIDLE
+            .has_keep_alive_idle_period = iaddr->has_keep_alive_idle_period,
+            .keep_alive_idle_period = iaddr->keep_alive_idle_period,
+#endif
         };
 
         (*addrs)[i] = newaddr;
diff --git a/meson.build b/meson.build
index 0ee79c664d..ca726f317f 100644
--- a/meson.build
+++ b/meson.build
@@ -2724,6 +2724,8 @@ config_host_data.set('HAVE_OPTRESET',
                      cc.has_header_symbol('getopt.h', 'optreset'))
 config_host_data.set('HAVE_IPPROTO_MPTCP',
                      cc.has_header_symbol('netinet/in.h', 'IPPROTO_MPTCP'))
+config_host_data.set('HAVE_TCP_KEEPIDLE',
+                     cc.has_header_symbol('netinet/tcp.h', 'TCP_KEEPIDLE'))
 
 # has_member
 config_host_data.set('HAVE_SIGEV_NOTIFY_THREAD_ID',
diff --git a/qapi/sockets.json b/qapi/sockets.json
index eb50f64e3a..ddd82b1e66 100644
--- a/qapi/sockets.json
+++ b/qapi/sockets.json
@@ -59,6 +59,10 @@
 # @keep-alive: enable keep-alive when connecting to/listening on this socket.
 #     (Since 4.2, not supported for listening sockets until 10.0)
 #
+# @keep-alive-idle-period: time in seconds the connection needs to be idle
+#     before sending a keepalive packet.  Only supported for TCP sockets on
+#     systems where TCP_KEEPIDLE socket option is defined.  (Since 10.0)
+#
 # @mptcp: enable multi-path TCP.  (Since 6.1)
 #
 # Since: 1.3
@@ -71,6 +75,7 @@
     '*ipv4': 'bool',
     '*ipv6': 'bool',
     '*keep-alive': 'bool',
+    '*keep-alive-idle-period': { 'type': 'uint32', 'if': 'HAVE_TCP_KEEPIDLE' },
     '*mptcp': { 'type': 'bool', 'if': 'HAVE_IPPROTO_MPTCP' } } }
 
 ##
diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c
index c30e4ac2ce..edcda846ef 100644
--- a/util/qemu-sockets.c
+++ b/util/qemu-sockets.c
@@ -349,6 +349,18 @@ listen_ok:
             slisten = -1;
             goto exit;
         }
+#ifdef HAVE_TCP_KEEPIDLE
+        if (saddr->has_keep_alive_idle_period && saddr->keep_alive_idle_period) {
+            int keepidle = saddr->has_keep_alive_idle_period;
+            ret = setsockopt(slisten, IPPROTO_TCP, TCP_KEEPIDLE, &keepidle, sizeof(keepidle));
+            if (ret < 0) {
+                error_setg_errno(errp, errno, "Unable to set TCP_KEEPIDLE");
+                close(slisten);
+                slisten = -1;
+                goto exit;
+            }
+        }
+#endif
     }
 exit:
     freeaddrinfo(res);
@@ -492,6 +504,17 @@ int inet_connect_saddr(InetSocketAddress *saddr, Error **errp)
             close(sock);
             return -1;
         }
+#ifdef HAVE_TCP_KEEPIDLE
+        if (saddr->has_keep_alive_idle_period && saddr->keep_alive_idle_period) {
+            int keepidle = saddr->keep_alive_idle_period;
+            ret = setsockopt(sock, IPPROTO_TCP, TCP_KEEPIDLE, &keepidle, sizeof(keepidle));
+            if (ret < 0) {
+                error_setg_errno(errp, errno, "Unsable to set TCP_KEEPIDLE");
+                close(sock);
+                return -1;
+            }
+        }
+#endif
     }
 
     return sock;
@@ -698,6 +721,22 @@ int inet_parse(InetSocketAddress *addr, const char *str, Error **errp)
         }
         addr->has_keep_alive = true;
     }
+#ifdef HAVE_TCP_KEEPIDLE
+    begin = strstr(optstr, ",keep-alive-idle-period=");
+    if (begin) {
+        begin += strlen(",keep-alive-idle-period=");
+        if (sscanf(begin, "%" PRIu32 "%n", &addr->keep_alive_idle_period, &pos) != 1 ||
+            (begin[pos] != '\0' && begin[pos] != ',')) {
+            error_setg(errp, "error parsing keep-alive-idle-period argument");
+            return -1;
+        }
+        if (addr->keep_alive_idle_period > INT_MAX) {
+            error_setg(errp, "keep-alive-idle-period value is too large");
+            return -1;
+        }
+        addr->has_keep_alive_idle_period = true;
+    }
+#endif
 #ifdef HAVE_IPPROTO_MPTCP
     begin = strstr(optstr, ",mptcp");
     if (begin) {
-- 
2.48.1