[PATCH] properly daemonize vncviewer

["Charles Coffing" <ccoffing@novell.com>]

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Hi,

Currently, vncviewer is spawned from xm, but it doesn't properly get
daemonized.  The attached patch makes vncviewer run completely separate
from xm.

There are various reasons it should be daemonized, but the particular
problem we hit was that YaST called "xm create" and waited on output on
stdout/stderr; xm then spawned vncviewer (which never closed its
inherited stdout and stderr); xm then would exit, but YaST still had
open file descriptors, and therefore waited forever.  It would be
possible to work around in YaST, but it seemed cleaner to daemonize
vncviewer.

We've been running with a variant of this patch (a variant because we
use tightvnc, which requires different arguments) for many months, and
it works well.

Please consider applying to xen-unstable.

Thanks.

Signed-off-by:  Charles Coffing <ccoffing@novell.com>


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Index: xen-unstable/tools/python/xen/xm/create.py
===================================================================
--- xen-unstable.orig/tools/python/xen/xm/create.py
+++ xen-unstable/tools/python/xen/xm/create.py
@@ -857,11 +857,49 @@ def choose_vnc_display():
 vncpid = None
 
 def spawn_vnc(display):
+    """Spawns a vncviewer that listens on the specified display.  On success,
+    returns the port that the vncviewer is listening on and sets the global
+    vncpid.  On failure, returns 0.  Note that vncviewer is daemonized.
+    """
     vncargs = (["vncviewer", "-log", "*:stdout:0",
             "-listen", "%d" % (VNC_BASE_PORT + display) ])
-    global vncpid    
-    vncpid = os.spawnvp(os.P_NOWAIT, "vncviewer", vncargs)
 
+    r, w = os.pipe()
+    pid = os.fork()
+
+    if pid == 0:
+        os.close(r)
+        w = os.fdopen(w, 'w')
+        os.setsid()
+        try:
+            pid2 = os.fork()
+        except:
+            pid2 = None
+        if pid2 == 0:
+            os.chdir("/")
+            for fd in range(0, 256):
+                try:
+                    os.close(fd)
+                except:
+                    pass
+            os.open("/dev/null", os.O_RDWR)
+            os.dup2(0, 1)
+            os.dup2(0, 2)
+            os.execvp("vncviewer", vncargs)
+            os._exit(1)
+        else:
+            w.write(str(pid2 or 0))
+            w.close()
+            os._exit(0)
+
+    global vncpid
+    os.close(w)
+    r = os.fdopen(r)
+    vncpid = int(r.read())
+    r.close()
+    os.waitpid(pid, 0)
+    if vncpid == 0:
+        return 0
     return VNC_BASE_PORT + display
     
 def preprocess_vnc(vals):

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