[ovs-dev] [PATCH] ofproto-dpif-xlate: Log flow in XLATE_REPORT().

[Joe Stringer]

To assist debugging pipelines when resubmit resource checks fail, print
the base_flow from the translation context. This base flow can then be
used from ofproto/trace to figure out which parts of the pipeline lead
to this translation error.

As far as I can see, the "## __VA_ARGS__" trick is a GCC thing rather
than part of the C standard, but it successfully compiles on GCC 6.1.1,
Clang 3.8.1, and the compiler that Appveyor CI uses so it seems like it
is widely supported.

Signed-off-by: Joe Stringer <joe at ovn.org>
---
 ofproto/ofproto-dpif-xlate.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/ofproto/ofproto-dpif-xlate.c b/ofproto/ofproto-dpif-xlate.c
index 393854e4bfc7..73ab3e558f9d 100644
--- a/ofproto/ofproto-dpif-xlate.c
+++ b/ofproto/ofproto-dpif-xlate.c
@@ -627,13 +627,20 @@ xlate_report(struct xlate_ctx *ctx, const char *format, ...)
 
 static struct vlog_rate_limit error_report_rl = VLOG_RATE_LIMIT_INIT(1, 5);
 
-#define XLATE_REPORT_ERROR(CTX, ...)                    \
-    do {                                                \
-        if (OVS_UNLIKELY((CTX)->xin->report_hook)) {    \
-            xlate_report(CTX, __VA_ARGS__);             \
-        } else {                                        \
-            VLOG_ERR_RL(&error_report_rl, __VA_ARGS__); \
-        }                                               \
+#define XLATE_REORDER(LAST, DUMMY, ...) __VA_ARGS__, LAST
+#define XLATE_REPORT_ERROR(CTX, FMT, ...)                               \
+    do {                                                                \
+        if (OVS_UNLIKELY((CTX)->xin->report_hook)) {                    \
+            xlate_report(CTX, FMT, ## __VA_ARGS__);                     \
+        } else {                                                        \
+            struct ds ds = DS_EMPTY_INITIALIZER;                        \
+                                                                        \
+            flow_format(&ds, &ctx->base_flow);                          \
+            VLOG_ERR_RL(&error_report_rl,                               \
+                        XLATE_REORDER(ds_cstr(&ds), dummy,              \
+                                      FMT": %s", ## __VA_ARGS__));      \
+            ds_destroy(&ds);                                            \
+        }                                                               \
     } while (0)
 
 static inline void
-- 
2.9.2