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xen-devel
Re: [Xen-devel] Re: [Xen-changelog] Detach Xend from terminal, courtesy
A second fork gets you reparented to init.
-Kip
On 12/9/05, Anthony Liguori <aliguori@xxxxxxxxxx> wrote:
Sorry I missed this on Xen devel, but could someone explain this patch a
little more. The old behavior purposefully delayed the terminal
detaching until Xend was ready to accept connections. This is necessary
to avoid a race condition with executing the first xm command after a
xend start.
I don't quite understand why two fork()s would be required to properly
daemonize. I don't know of any other daemons that do that (certainly,
xenstored and xenconsoled don't).
I could be missing something so if someone could clarify I'd greatly
appreciate it.
Thanks,
Anthony Liguori
Xen patchbot -unstable wrote:
># HG changeset patch
># User emellor@xxxxxxxxxxxxxxxxxxxxxx
># Node ID efc71a3e9f6f7487ad349677369d6221a06ead3f
># Parent 52f214d983fb3edf2e265984ed9fe103dd7d2440
>Detach Xend from terminal, courtesy of Horms <horms@xxxxxxxxxxxx
>.
>
>* For setsid to effectively detach a process from the terminal,
> the following needs to occur:
>
> fork () Return control to the shell
> setsid () New session with no controlling terminal
> fork () The session leader (parent) exits and thus
> the
resulting child process can never regain the terminal
>
> This patch adds the second fork
>
>* The call to self.daemonize(), which now forks, is moved to
> run before self.tracing(), as now that it actually disconnects
> from the terminal, and thus the prevailing process, the trace
> loses the processes created in self.run().
>
>Signed-off-by: Ewan Mellor <ewan@xxxxxxxxxxxxx
>
>
>diff -r 52f214d983fb -r efc71a3e9f6f tools/python/xen/xend/server/SrvDaemon.py
>--- a/tools/python/xen/xend/server/SrvDaemon.py Thu Dec 8 16:11:48 2005
>+++ b/tools/python/xen/xend/server/SrvDaemon.py Thu Dec 8 16:17:53 2005
>@@ -123,9 +123,18 @@
>
> def daemonize(self):
> if not XEND_DAEMONIZE: return
>+
> # Detach from TTY.
>+
>+ # Become the group leader (already a child process)
> os.setsid()
>
>+ # Fork, this allows the group leader to exit,
>+ # which means the child can never again regain control of the
>+ # terminal
>+ if
self.fork_pid(XEND_PID_FILE):
>+ self.exit()
>+
> # Detach from standard file descriptors, and redirect them to
> # /dev/null or the log as appropriate.
> os.close
(0)
>@@ -164,7 +173,7 @@
> # we can avoid a race condition during startup
>
> r,w = os.pipe()
>- if self.fork_pid(XEND_PID_FILE):
>+ if os.fork():
>
os.close(w)
> r = os.fdopen(r, 'r')
> try:
>@@ -178,6 +187,7 @@
> else:
> os.close(r)
> # Child
>+ self.daemonize
()
> self.tracing(trace)
> self.run(os.fdopen(w, 'w'))
>
>@@ -274,7 +284,6 @@
>
> relocate.listenRelocation()
> servers = SrvServer.create
()
>- self.daemonize()
> servers.start(status)
> except Exception, ex:
>
print >>sys.stderr, 'Exception starting xend:', ex
>
>_______________________________________________
>Xen-changelog mailing list
>Xen-changelog@xxxxxxxxxxxxxxxxxxx
>http://lists.xensource.com/xen-changelog
>
>
>
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