Commit aec21d3175 (qapi: Add InetSocketAddress member keep-alive)
introduces the keep-alive flag, which enables the SO_KEEPALIVE socket
option, but only on client-side sockets. However, this option is also
useful for server-side sockets, so they can check if a client is still
reachable or drop the connection otherwise.

This patch enables the SO_KEEPALIVE socket option on passive server-side
sockets if the keep-alive flag is enabled. This socket option is then
inherited by active server-side sockets communicating with connected
clients.

This patch also fixes an issue in 'qio_dns_resolver_lookup_sync_inet()'
where the keep-alive flag is not copied together with other attributes.

Signed-off-by: Juraj Marcin <jmarcin@redhat.com>
---
 io/dns-resolver.c   |  2 ++
 qapi/sockets.json   |  4 ++--
 util/qemu-sockets.c | 19 +++++++++++++------
 3 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/io/dns-resolver.c b/io/dns-resolver.c
index 53b0e8407a..ee7403b65b 100644
--- a/io/dns-resolver.c
+++ b/io/dns-resolver.c
@@ -126,6 +126,8 @@ static int qio_dns_resolver_lookup_sync_inet(QIODNSResolver *resolver,
             .has_mptcp = iaddr->has_mptcp,
             .mptcp = iaddr->mptcp,
 #endif
+            .has_keep_alive = iaddr->has_keep_alive,
+            .keep_alive = iaddr->keep_alive,
         };
 
         (*addrs)[i] = newaddr;
diff --git a/qapi/sockets.json b/qapi/sockets.json
index 6a95023315..eb50f64e3a 100644
--- a/qapi/sockets.json
+++ b/qapi/sockets.json
@@ -56,8 +56,8 @@
 # @ipv6: whether to accept IPv6 addresses, default try both IPv4 and
 #     IPv6
 #
-# @keep-alive: enable keep-alive when connecting to this socket.  Not
-#     supported for passive sockets.  (Since 4.2)
+# @keep-alive: enable keep-alive when connecting to/listening on this socket.
+#     (Since 4.2, not supported for listening sockets until 10.0)
 #
 # @mptcp: enable multi-path TCP.  (Since 6.1)
 #
diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c
index 77477c1cd5..c30e4ac2ce 100644
--- a/util/qemu-sockets.c
+++ b/util/qemu-sockets.c
@@ -220,12 +220,6 @@ static int inet_listen_saddr(InetSocketAddress *saddr,
     int saved_errno = 0;
     bool socket_created = false;
 
-    if (saddr->keep_alive) {
-        error_setg(errp, "keep-alive option is not supported for passive "
-                   "sockets");
-        return -1;
-    }
-
     memset(&ai,0, sizeof(ai));
     ai.ai_flags = AI_PASSIVE;
     if (saddr->has_numeric && saddr->numeric) {
@@ -344,6 +338,19 @@ listen_failed:
     return -1;
 
 listen_ok:
+    if (saddr->keep_alive) {
+        int val = 1;
+        int ret = setsockopt(slisten, SOL_SOCKET, SO_KEEPALIVE,
+                             &val, sizeof(val));
+
+        if (ret < 0) {
+            error_setg_errno(errp, errno, "Unable to set KEEPALIVE");
+            close(slisten);
+            slisten = -1;
+            goto exit;
+        }
+    }
+exit:
     freeaddrinfo(res);
     return slisten;
 }
-- 
2.48.1