glib-unix: Add O_NONBLOCK support to g_unix_open_pipe()

Add support for it, but don’t use it anywhere yet — this is an API
addition, but currently doesn’t cause any functional changes. It’ll be
used in the next commit.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

gio/gtestdbus.c

@@ -249,7 +249,7 @@ watcher_init (void)
       gint pipe_fds[2];
 
       /* fork a child to clean up when we are killed */
-      if (!g_unix_open_pipe_internal (pipe_fds, TRUE))
+      if (!g_unix_open_pipe_internal (pipe_fds, TRUE, FALSE))
         {
           errsv = errno;
           g_warning ("pipe() failed: %s", g_strerror (errsv));

glib/gbacktrace.c

@@ -398,8 +398,8 @@ stack_trace (const char * const *args)
   stack_trace_done = FALSE;
   signal (SIGCHLD, stack_trace_sigchld);
 
-  if (!g_unix_open_pipe_internal (in_fd, TRUE) ||
+  if (!g_unix_open_pipe_internal (in_fd, TRUE, FALSE) ||
-      !g_unix_open_pipe_internal (out_fd, TRUE))
+      !g_unix_open_pipe_internal (out_fd, TRUE, FALSE))
     {
       perror ("unable to open pipe");
       _exit (0);

glib/glib-unix.c

@@ -74,11 +74,16 @@ g_unix_set_error_from_errno (GError **error,
  *
  * Similar to the UNIX pipe() call, but on modern systems like Linux
  * uses the pipe2() system call, which atomically creates a pipe with
- * the configured flags. The only supported flag currently is
+ * the configured flags.
- * %FD_CLOEXEC. If for example you want to configure %O_NONBLOCK, that
- * must still be done separately with fcntl().
  *
- * This function does not take %O_CLOEXEC, it takes %FD_CLOEXEC as if
+ * As of GLib 2.78, the supported flags are `FD_CLOEXEC` and `O_NONBLOCK`. Prior
+ * to GLib 2.78, only `FD_CLOEXEC` was supported — if you wanted to configure
+ * `O_NONBLOCK` then that had to be done separately with `fcntl()`.
+ *
+ * It is a programmer error to call this function with unsupported flags, and a
+ * critical warning will be raised.
+ *
+ * This function does not take `O_CLOEXEC`, it takes `FD_CLOEXEC` as if
  * for fcntl(); these are different on Linux/glibc.
  *
  * Returns: %TRUE on success, %FALSE if not (and errno will be set).
@@ -90,11 +95,12 @@ g_unix_open_pipe (int     *fds,
                   int      flags,
                   GError **error)
 {
-  /* We only support FD_CLOEXEC */
+  /* We only support FD_CLOEXEC and O_NONBLOCK */
-  g_return_val_if_fail ((flags & (FD_CLOEXEC)) == flags, FALSE);
+  g_return_val_if_fail ((flags & (FD_CLOEXEC | O_NONBLOCK)) == flags, FALSE);
 
   if (!g_unix_open_pipe_internal (fds,
-                                  (flags & FD_CLOEXEC) != 0))
+                                  (flags & FD_CLOEXEC) != 0,
+                                  (flags & O_NONBLOCK) != 0))
     return g_unix_set_error_from_errno (error, errno);
 
   return TRUE;

glib/glib-unixprivate.h

@@ -41,15 +41,22 @@ G_BEGIN_DECLS
 
 static inline gboolean
 g_unix_open_pipe_internal (int *fds,
-                           gboolean close_on_exec)
+                           gboolean close_on_exec,
+                           gboolean nonblock)
   {
 #ifdef HAVE_PIPE2
   do
     {
       int ecode;
+      int flags = 0;
+
+      if (close_on_exec)
+        flags |= O_CLOEXEC;
+      if (nonblock)
+        flags |= O_NONBLOCK;
 
       /* Atomic */
-      ecode = pipe2 (fds, close_on_exec ? O_CLOEXEC : 0);
+      ecode = pipe2 (fds, flags);
       if (ecode == -1 && errno != ENOSYS)
         return FALSE;
       else if (ecode == 0)
@@ -62,21 +69,44 @@ g_unix_open_pipe_internal (int *fds,
   if (pipe (fds) == -1)
     return FALSE;
 
-  if (!close_on_exec)
+  if (close_on_exec)
-    return TRUE;
-
-  if (fcntl (fds[0], F_SETFD, FD_CLOEXEC) == -1 ||
-      fcntl (fds[1], F_SETFD, FD_CLOEXEC) == -1)
     {
-      int saved_errno = errno;
+      if (fcntl (fds[0], F_SETFD, FD_CLOEXEC) == -1 ||
+          fcntl (fds[1], F_SETFD, FD_CLOEXEC) == -1)
+        {
+          int saved_errno = errno;
 
-      close (fds[0]);
+          close (fds[0]);
-      close (fds[1]);
+          close (fds[1]);
-      fds[0] = -1;
+          fds[0] = -1;
-      fds[1] = -1;
+          fds[1] = -1;
 
-      errno = saved_errno;
+          errno = saved_errno;
-      return FALSE;
+          return FALSE;
+        }
+    }
+
+  if (nonblock)
+    {
+#ifdef O_NONBLOCK
+      int flags = O_NONBLOCK;
+#else
+      int flags = O_NDELAY;
+#endif
+
+      if (fcntl (fds[0], F_SETFL, flags) == -1 ||
+          fcntl (fds[1], F_SETFL, flags) == -1)
+        {
+          int saved_errno = errno;
+
+          close (fds[0]);
+          close (fds[1]);
+          fds[0] = -1;
+          fds[1] = -1;
+
+          errno = saved_errno;
+          return FALSE;
+        }
     }
 
   return TRUE;