select: Don't timeout without setting descriptor arrays to all zero

        * select.cc (copyfd_set): Remove.
        (select): Don't copy local wait fd arrays over to returned fd arrays
        since bits set there are not accounted for in return value.  Zero out
        returned fd arrays instead.  Always call sel.poll even in case of a
        timeout.  Always zero out fd array when timing out.  Convert while/do
        to do/while for clarity.  Use dedicated variable as return value to
        decouple return value from artificial return code from sel.wait.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

1 files changed, 20 insertions, 15 deletions

diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc
index 524e578ae..b4c37783a 100644
--- a/winsup/cygwin/select.cc
+++ b/winsup/cygwin/select.cc
@@ -77,8 +77,6 @@ details. */
   (fd_set *) __res; \
 })
 
-#define copyfd_set(to, from, n) memcpy (to, from, sizeof_fd_set (n));
-
 #define set_handle_or_return_if_not_open(h, s) \
   h = (s)->fh->get_io_handle_cyg (); \
   if (cygheap->fdtab.not_open ((s)->fd)) \
@@ -132,6 +130,7 @@ select (int maxfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
 	DWORD ms)
 {
   int res = select_stuff::select_loop;
+  int ret = 0;
 
   /* Record the current time for later use. */
   LONGLONG start_time = gtod.msecs ();
@@ -144,7 +143,7 @@ select (int maxfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
   fd_set *w = allocfd_set (maxfds);
   fd_set *e = allocfd_set (maxfds);
 
-  while (res == select_stuff::select_loop)
+  do
     {
       /* Build the select record per fd linked list and set state as
 	 needed. */
@@ -187,14 +186,15 @@ select (int maxfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
       select_printf ("res %d", res);
       if (res >= 0)
 	{
-	  copyfd_set (readfds, r, maxfds);
-	  copyfd_set (writefds, w, maxfds);
-	  copyfd_set (exceptfds, e, maxfds);
-	  if (res == select_stuff::select_set_zero)
-	    res = 0;
-	  else
-	    /* Set the bit mask from sel records */
-	    res = sel.poll (readfds, writefds, exceptfds) ?: select_stuff::select_loop;
+	  UNIX_FD_ZERO (readfds, maxfds);
+	  UNIX_FD_ZERO (writefds, maxfds);
+	  UNIX_FD_ZERO (exceptfds, maxfds);
+	  /* Set bit mask from sel records even in case of a timeout so we
+	     don't miss one.  This also sets ret to the right value >= 0,
+	     matching the number of bits set in the fds records. */
+	  ret = sel.poll (readfds, writefds, exceptfds);
+	  if (!ret && res != select_stuff::select_set_zero)
+	    res = select_stuff::select_loop;
 	}
       /* Always clean up everything here.  If we're looping then build it
 	 all up again.  */
@@ -208,7 +208,11 @@ select (int maxfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
 	  if (now > (start_time + ms))
 	    {
 	      select_printf ("timed out after verification");
-	      res = 0;
+	      /* Set descriptor bits to zero per POSIX. */
+	      UNIX_FD_ZERO (readfds, maxfds);
+	      UNIX_FD_ZERO (writefds, maxfds);
+	      UNIX_FD_ZERO (exceptfds, maxfds);
+	      ret = res = 0;
 	    }
 	  else
 	    {
@@ -218,10 +222,11 @@ select (int maxfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
 	    }
 	}
     }
+  while (res == select_stuff::select_loop);
 
-  if (res < -1)
-    res = -1;
-  return res;
+  if (res < 0)
+    ret = -1;
+  return ret;
 }
 
 extern "C" int