[Qemu-devel] [Patch] Publish VNC display with zeroconf

[Oliver Gerlich]

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Hi,

here's a little gimmick for VNC support :-)

The patch makes Qemu publish its VNC display via zeroconf if it is
called with -vnc option. The patch uses the avahi-publish helper app for
this, which comes with the Avahi suite (eg. in Debian and Ubuntu it's in
the avahi-utils package). If avahi-publish is not installed, this patch
won't do anything.

With the patch applied, you can use the service-discovery-applet under
Gnome to see all Qemu instances which use VNC. Under KDE, Krdc offers a
list of all zeroconf-published VNC displays (choose "DNS-SD" from the
listbox in the upper left corner in Krdc).


Regards,
Oliver
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--- qemu-0.8.1/vnc.c    2006-05-03 22:32:58.000000000 +0200
+++ qemu-0.8.1-avahi/vnc.c      2006-05-14 16:21:05.000000000 +0200
@@ -64,6 +64,11 @@
     size_t read_handler_expect;
 };
 
+#ifndef _WIN32
+#include <signal.h>
+pid_t mdns_publish_pid = 0;
+#endif
+
 /* TODO
    1) Get the queue working for IO.
    2) there is some weirdness when using the -S option (the screen is grey
@@ -852,6 +857,71 @@
     }
 }
 
+#ifndef _WIN32
+static void vnc_unpublish_mdns(void)
+{
+    if (mdns_publish_pid != 0)
+    {
+        kill(mdns_publish_pid, SIGTERM);
+    }
+    return;
+}
+#endif
+
+/// Publish VNC display via mdns/zeroconf using the Avahi suite.
+/// See RFC 2782 and avahi-publish(1) for more info.
+void vnc_publish_mdns(int port)
+{
+#ifndef _WIN32
+    // Execute avahi helper program in a child process.
+    pid_t childPid = fork();
+    switch(childPid)
+    {
+        case -1:
+            // fork() failed; ignore this.
+            break;
+
+        case 0:
+        {
+            // New child process.
+            char name[250];
+            char portString[10];
+            char *argv[10];
+            int i = 0;
+
+            sprintf(name, "QEMU instance on port %d", port);
+            sprintf(portString, "%d", port);
+
+            argv[i++] = "avahi-publish"; // avahi-publish is a helper program 
from Avahi that publishes DNS-SD records.
+            argv[i++] = "-s";            // Flag: publish a service.
+            argv[i++] = name;            // Name of the service
+            argv[i++] = "_rfb._tcp";     // Service type (see 
http://www.dns-sd.org/ServiceTypes.html)
+            argv[i++] = portString;      // TCP port
+            argv[i++] = NULL;
+
+            // Close stdout/stderr to suppress output from avahi-publish
+            close(STDOUT_FILENO);
+            close(STDERR_FILENO);
+
+            // Execute avahi-publish
+            execvp(argv[0], argv);
+
+            // This point might be reached, eg. if avahi-publish is not 
installed.
+            exit(0);
+            break;
+        }
+
+        default:
+            // Parent process. Record child pid and set exit handler.
+            mdns_publish_pid = childPid;
+            atexit(vnc_unpublish_mdns);
+            break;
+    }
+#endif
+
+    return;
+}
+
 void vnc_display_init(DisplayState *ds, int display)
 {
     struct sockaddr_in addr;
@@ -918,4 +988,6 @@
     memset(vs->dirty_row, 0xFF, sizeof(vs->dirty_row));
 
     vnc_dpy_resize(vs->ds, 640, 400);
+
+    vnc_publish_mdns(5900 + display);
 }