run_erl: Fix failing run_erl invokation on OpenBSD

Symptom: run_erl does exit(0) and child program (erl) does
not seem to start.  Running run_erl again however brings the previous
child program to life.

Problem: A race causing run_erl to read 0 from master pty and exit
because the child has not yet opened its corresponding slave pty.

Solution: Use the non standard openpty() function instead that does
not expose this race as the slave fd is opened in the parent.


Question:
Is there a race free way to do this with posix_openpt on OpenBSD?

1 files changed, 14 insertions, 2 deletions

diff --git a/erts/etc/unix/run_erl.c b/erts/etc/unix/run_erl.c
index d7cfbe675e..f8b5da47ab 100644
--- a/erts/etc/unix/run_erl.c
+++ b/erts/etc/unix/run_erl.c
@@ -904,14 +904,26 @@ static int create_fifo(char *name, int perm)
  * Find a master device, open and return fd and slave device name.
  */
 
+#ifdef HAVE_WORKING_POSIX_OPENPT
+   /*
+    * Use openpty() on OpenBSD even if we have posix_openpt()
+    * as there is a race when read from master pty returns 0
+    * if child has not yet opened slave pty.
+    * (maybe other BSD's have the same problem?)
+    */
+#  if !(defined(__OpenBSD__) && defined(HAVE_OPENPTY))
+#    define TRY_POSIX_OPENPT
+#  endif
+#endif
+
 static int open_pty_master(char **ptyslave, int *sfdp)
 {
   int mfd;
 
 /* Use the posix_openpt if working, as this guarantees creation of the 
    slave device properly. */
-#if defined(HAVE_WORKING_POSIX_OPENPT) || (defined(__sun) && defined(__SVR4))
-#  ifdef HAVE_WORKING_POSIX_OPENPT
+#if defined(TRY_POSIX_OPENPT) || (defined(__sun) && defined(__SVR4))
+#  ifdef TRY_POSIX_OPENPT
   mfd = posix_openpt(O_RDWR);
 #  elif defined(__sun) && defined(__SVR4)
   mfd = sf_open("/dev/ptmx", O_RDWR, 0);