Re: [PATCH] properly daemonize vncviewer

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

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On Wed, Aug 2, 2006 at  2:32 AM, Keir Fraser <Keir.Fraser@cl.cam.ac.uk>
wrote: 
> On 1 Aug 2006, at 20:11, Charles Coffing wrote:
> 
>> 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.
> 
> Is there no Python library function that can do this (I couldn't find

> one)?

No.  And as an added twist, I wanted to get the PID of the daemonized
program back (without the mess or risk of writing to a temporary file)
and I didn't see any such thing out there already.

> If not, can you at least put the new code in a function with a 
> spawn- like interface (i.e., takes two parameters --  program name
and 
> program argument list). It's okay to put the new function somewhere 
> nearby in create.py.

I've attached the updated patch with the suggested changes.



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Index: xen-3.0-testing/tools/python/xen/xm/create.py
===================================================================
--- xen-3.0-testing.orig/tools/python/xen/xm/create.py
+++ xen-3.0-testing/tools/python/xen/xm/create.py
@@ -765,14 +765,58 @@ def choose_vnc_display():
 
 vncpid = None
 
+def daemonize(prog, args):
+    """Runs a program as a daemon with the list of arguments.  Returns the PID
+    of the daemonized program, or returns 0 on error.
+    """
+    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(prog, args)
+            os._exit(1)
+        else:
+            w.write(str(pid2 or 0))
+            w.close()
+            os._exit(0)
+
+    os.close(w)
+    r = os.fdopen(r)
+    daemon_pid = int(r.read())
+    r.close()
+    os.waitpid(pid, 0)
+    return daemon_pid
+
 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)
-
+    global vncpid
+    vncpid = daemonize("vncviewer", vncargs)
+    if vncpid == 0:
+        return 0
     return VNC_BASE_PORT + display
-    
+
 def preprocess_vnc(vals):
     """If vnc was specified, spawn a vncviewer in listen mode
     and pass its address to the domain on the kernel command line.

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