[Qemu-devel] [PATCH v2] glib-compat: work around g_test_message bug with subprocess tests

[Paolo Bonzini <pbonzini@redhat.com>]

Subprocesses are created by glib without leaving the file descriptors
open.  Therefore, g_test_message (and assertion failures, but those
trigger when things are going bad anyway) will think that it is writing
to the log file descriptor, but while actually stomping on the QMP
file descriptor or similar.  This causes spurious failures, which are
as nice to debug as the reader can imagine.  While I have opened a
pull request on GLib, this will probably take a while to propagate
to distros.

I found this while working on qgraph, but the fix is generic.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1543343726-53531-1-git-send-email-pbonzini@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 include/glib-compat.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/glib-compat.h b/include/glib-compat.h
index fdf95a255d..f675c7328f 100644
--- a/include/glib-compat.h
+++ b/include/glib-compat.h
@@ -113,4 +113,12 @@ gint g_poll_fixed(GPollFD *fds, guint nfds, gint timeout);
 
 #pragma GCC diagnostic pop
 
+/* See https://gitlab.gnome.org/GNOME/glib/merge_requests/501 */
+#define g_test_message(...)                                     \
+    do {                                                        \
+        if (!g_test_subprocess()) {                             \
+            g_test_message(__VA_ARGS__);                        \
+        }                                                       \
+    } while (0)
+
 #endif
-- 
2.19.1