[Qemu-devel] PATCH: enabling TCP keepalives on VNC connections

["David S. Ahern" <daahern@cisco.com>]

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This patch enables TCP keepalives on VNC connections for linux hosts.
After 60-seconds of idle time, probes are sent every 12 seconds with the
connection resetting after 5 failed probes (ie., connection is closed if
no response received in 60-seconds).

Signed-off-by: David Ahern <dsahern@gmail.com>


david

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diff --git a/vnc.c b/vnc.c
index ab1f044..7a8bbd7 100644
--- a/vnc.c
+++ b/vnc.c
@@ -32,6 +32,12 @@
 
 #define VNC_REFRESH_INTERVAL (1000 / 30)
 
+#ifdef __linux__
+#define VNC_TCP_KEEPIDLE  60
+#define VNC_TCP_KEEPINTVL 12
+#define VNC_TCP_KEEPCNT    5
+#endif
+
 #include "vnc_keysym.h"
 #include "d3des.h"
 
@@ -2015,12 +2021,41 @@ static void vnc_listen_read(void *opaque)
     VncDisplay *vs = opaque;
     struct sockaddr_in addr;
     socklen_t addrlen = sizeof(addr);
+    int val;
 
     /* Catch-up */
     vga_hw_update();
 
     int csock = accept(vs->lsock, (struct sockaddr *)&addr, &addrlen);
     if (csock != -1) {
+#ifdef __linux__
+        /* best effort to enable keep alives */
+        val = 1;
+        if (setsockopt(csock, SOL_SOCKET, SO_KEEPALIVE,
+                       &val, sizeof(val)) < 0) {
+            fprintf(stderr, "VNC: failed to enable keepalives\n");
+        }
+
+        /* after N-seconds of idle time, send probes every X seconds
+         * dropping the connection after Y failed probes.
+         */
+        val = VNC_TCP_KEEPIDLE;
+        if (setsockopt(csock, IPPROTO_TCP, TCP_KEEPIDLE,
+                       &val, sizeof(val)) < 0) {
+            fprintf(stderr, "VNC: failed to set tcp idle interval\n");
+        }
+        val = VNC_TCP_KEEPINTVL;
+        if (setsockopt(csock, IPPROTO_TCP, TCP_KEEPINTVL,
+                       &val, sizeof(val)) < 0) {
+            fprintf(stderr, "VNC: failed to set tcp probe interval\n");
+        }
+        val = VNC_TCP_KEEPCNT;
+        if (setsockopt(csock, IPPROTO_TCP, TCP_KEEPCNT,
+                       &val, sizeof(val)) < 0) {
+            fprintf(stderr, "VNC: failed to set tcp missed probe count\n");
+        }
+#endif
+
         vnc_connect(vs, csock);
     }
 }