[PATCH 2/4] Go away when the mountee has been shut down.

[Sergiu Ivanov]

* mount.c (mountee_control): New variable.
(mountee_notify_port): Likewise.
(start_mountee): Store the control port of the mountee in
the global variable mountee_control.
(mountee_server): New function.
(_mountee_listen_thread_proc): Likewise.
(setup_unionmount): Request to be notified when the mountee goes
away.  Detach a separate thread to wait for the notification.
* mount.h (mountee_control): New variable.
---
Hello,

On Sun, Aug 16, 2009 at 09:55:26PM +0200, olafBuddenhagen@gmx.net wrote:
> On Mon, Aug 03, 2009 at 11:37:50PM +0300, Sergiu Ivanov wrote:
> > On Wed, Jul 29, 2009 at 10:47:53AM +0200, olafBuddenhagen@gmx.net wrote:
> > > On Fri, Jul 17, 2009 at 01:57:33PM +0300, Sergiu Ivanov wrote:
>
> > > > +static void
> > > > +_mountee_listen_thread_proc (any_t * arg)
> > > > +{
> > > > +  while (1)
> > > > +    mach_msg_server (mountee_server, 0, mountee_listen_port);
> > > > +}                              /* _mountee_listen_thread */
> > > 
> > > The comment here seems pointless, when the function started only a few
> > > lines above...
> > > 
> > > Also, it's wrong :-)
> > 
> > I'm not sure I can correctly understand what you are talking about :-(
> 
> I'm talkin about the "/* _mountee_listen_thread */" comment at the end
> of the function. These comments might be useful for long functions,
> where the beginning is not visible while looking at the end -- but for a
> function that only has a few lines, it's pointless. It's just an
> unnecessary maintenance burden -- it seems that you actually forgot to
> update it at some point, as the comment doesn't match the function name.
 
I see...  I've removed the comment.

I generally like to put such comments after the final closing brace of
the function because it helps me greatly when I walking through the
code, but it never really occurred to me that short functions don't
need such decoration :-(

Regards,
scolobb

---
 mount.c |   67 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 mount.h |    1 +
 2 files changed, 65 insertions(+), 3 deletions(-)

diff --git a/mount.c b/mount.c
index 51140be..214edbf 100644
--- a/mount.c
+++ b/mount.c
@@ -24,6 +24,7 @@
 
 #include <hurd/fsys.h>
 #include <fcntl.h>
+#include <cthreads.h>
 
 #include "mount.h"
 #include "lib.h"
@@ -34,6 +35,7 @@ char * mountee_argz;
 size_t mountee_argz_len;
 
 mach_port_t mountee_root;
+mach_port_t mountee_control = MACH_PORT_NULL;
 
 int mountee_started = 0;
 
@@ -41,6 +43,10 @@ int mountee_started = 0;
    operates (transparent/non-transparent).  */
 int transparent_mount = 1;
 
+/* The port for receiving the notification about the shutdown of the
+   mountee.  */
+mach_port_t mountee_notify_port;
+
 /* Starts the mountee (given by `argz` and `argz_len`), attaches it to
    the node `np` and opens a port `port` to the mountee with
    `flags`.  */
@@ -51,8 +57,6 @@ start_mountee (node_t * np, char * argz, size_t argz_len, int 
flags,
   error_t err;
   mach_port_t underlying_port;
 
-  mach_port_t mountee_control;
-
   /* Identity information about the unionfs process (for
      fsys_getroot).  */
   uid_t * uids;
@@ -133,6 +137,31 @@ start_mountee (node_t * np, char * argz, size_t argz_len, 
int flags,
   return err;
 }                              /* start_mountee */
 
+/* Listens to the MACH_NOTIFY_DEAD_NAME notification for the port on
+   the control port of the mountee.  */
+error_t
+mountee_server (mach_msg_header_t * inp, mach_msg_header_t * outp)
+{
+  if (inp->msgh_id == MACH_NOTIFY_DEAD_NAME)
+    {
+      /* Terminate operations conducted by unionfs and shut down.  */
+      netfs_shutdown (FSYS_GOAWAY_FORCE);
+      exit (0);
+    }
+
+  return 1;
+}                              /* mountee_server */
+
+/* The main proc of the thread for listening for the
+   MACH_NOTIFY_DEAD_NAME notification on the control port of the
+   mountee.  */
+static void
+_mountee_listen_thread_proc (any_t * arg)
+{
+  while (1)
+    mach_msg_server (mountee_server, 0, mountee_notify_port);
+}
+
 /* Sets up a proxy node, sets the translator on it, and registers the
    filesystem published by the translator in the list of merged
    filesystems.  */
@@ -158,6 +187,38 @@ setup_unionmount (void)
 
   mountee_started = 1;
 
-  return 0;
+  /* The previously registered send-once right (used to hold the value
+     returned from mach_port_request_notification) */
+  mach_port_t prev;
+
+  /* Setup the port for receiving notifications.  */
+  err = mach_port_allocate (mach_task_self (), MACH_PORT_RIGHT_RECEIVE,
+                     &mountee_notify_port);
+  if (err)
+    return err;
+  err = mach_port_insert_right (mach_task_self (), mountee_notify_port,
+                               mountee_notify_port, MACH_MSG_TYPE_MAKE_SEND);
+  if (err)
+    {
+      mach_port_deallocate (mach_task_self (), mountee_notify_port);
+      return err;
+    }
+
+  /* Request to be notified when the mountee goes away and
+     `mountee_control` becomes a dead name.  */
+  err = mach_port_request_notification (mach_task_self (), mountee_control,
+                                       MACH_NOTIFY_DEAD_NAME, 1, 
mountee_notify_port,
+                                       MACH_MSG_TYPE_MAKE_SEND_ONCE, &prev);
+  assert (prev == MACH_PORT_NULL);
+  if(err)
+    {
+      mach_port_deallocate (mach_task_self(), mountee_notify_port);
+      return err;
+    }
+
+  /* Create a new thread for listening to the notification.  */
+  cthread_detach (cthread_fork ((cthread_fn_t) _mountee_listen_thread_proc, 
NULL));
+
+  return err;
 }                              /* setup_unionmount */
 
diff --git a/mount.h b/mount.h
index d51fdeb..e82c45c 100644
--- a/mount.h
+++ b/mount.h
@@ -34,6 +34,7 @@ extern char * mountee_argz;
 extern size_t mountee_argz_len;
 
 extern mach_port_t mountee_root;
+extern mach_port_t mountee_control;
 
 extern int mountee_started;
 
-- 
1.6.3.3