* fhandler_serial.cc (fhandler_serial::raw_read): Just call ReadFile

	directly in case of non-blocking I/O and handle result gracefully.

1 files changed, 9 insertions, 12 deletions

diff --git a/winsup/cygwin/fhandler_serial.cc b/winsup/cygwin/fhandler_serial.cc
index 677b6221f..c58d0418c 100644
--- a/winsup/cygwin/fhandler_serial.cc
+++ b/winsup/cygwin/fhandler_serial.cc
@@ -71,7 +71,7 @@ fhandler_serial::raw_read (void *ptr, size_t& ulen)
 	termios_printf ("error detected %x", ev);
       else if (st.cbInQue && !vtime_)
 	inq = st.cbInQue;
-      else if (!overlapped_armed)
+      else if (!is_nonblocking () && !overlapped_armed)
 	{
 	  if ((size_t) tot >= minchars)
 	    break;
@@ -83,16 +83,6 @@ fhandler_serial::raw_read (void *ptr, size_t& ulen)
 	    }
 	  else if (GetLastError () != ERROR_IO_PENDING)
 	    goto err;
-	  else if (is_nonblocking ())
-	    {
-	      PurgeComm (get_handle (), PURGE_RXABORT);
-	      if (tot == 0)
-		{
-		  tot = -1;
-		  set_errno (EAGAIN);
-		}
-	      goto out;
-	    }
 	  else
 	    {
 	      overlapped_armed = 1;
@@ -132,7 +122,14 @@ fhandler_serial::raw_read (void *ptr, size_t& ulen)
 	goto err;
       else if (is_nonblocking ())
 	{
-	  PurgeComm (get_handle (), PURGE_RXABORT);
+	  /* Use CancelIo rather than PurgeComm (PURGE_RXABORT) since
+	     PurgeComm apparently discards in-flight bytes while CancelIo
+	     only stops the overlapped IO routine. */
+	  CancelIo (get_handle ());
+	  if (GetOverlappedResult (get_handle (), &io_status, &n, FALSE))
+	    tot = n;
+	  else if (GetLastError () != ERROR_IO_INCOMPLETE)
+	    goto err;
 	  if (tot == 0)
 	    {
 	      tot = -1;