[PATCH 08/11] fsmonitor: log invocation of FSMonitor hook to trace2

["Jeff Hostetler via GitGitGadget" <gitgitgadget@gmail.com>]

From: Jeff Hostetler <jeffhost@microsoft.com>

Let's measure the time taken to request and receive FSMonitor data
via the hook API and the size of the response.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
---
 fsmonitor.c | 29 ++++++++++++++++++++++++++++-
 fsmonitor.h |  5 +++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/fsmonitor.c b/fsmonitor.c
index ca031c3abb8..7a2be24cd43 100644
--- a/fsmonitor.c
+++ b/fsmonitor.c
@@ -142,6 +142,7 @@ void write_fsmonitor_extension(struct strbuf *sb, struct index_state *istate)
 static int query_fsmonitor(int version, const char *last_update, struct strbuf *query_result)
 {
 	struct child_process cp = CHILD_PROCESS_INIT;
+	int result;
 
 	if (!core_fsmonitor)
 		return -1;
@@ -152,7 +153,33 @@ static int query_fsmonitor(int version, const char *last_update, struct strbuf *
 	cp.use_shell = 1;
 	cp.dir = get_git_work_tree();
 
-	return capture_command(&cp, query_result, 1024);
+	trace2_region_enter("fsm_hook", "query", NULL);
+
+	result = capture_command(&cp, query_result, 1024);
+
+	if (result)
+		trace2_data_intmax("fsm_hook", NULL, "query/failed", result);
+	else {
+		trace2_data_intmax("fsm_hook", NULL, "query/response-length",
+				   query_result->len);
+
+		if (fsmonitor_is_trivial_response(query_result))
+			trace2_data_intmax("fsm_hook", NULL,
+					   "query/trivial-response", 1);
+	}
+
+	trace2_region_leave("fsm_hook", "query", NULL);
+
+	return result;
+}
+
+int fsmonitor_is_trivial_response(const struct strbuf *query_result)
+{
+	static char trivial_response[3] = { '\0', '/', '\0' };
+	int is_trivial = !memcmp(trivial_response,
+				 &query_result->buf[query_result->len - 3], 3);
+
+	return is_trivial;
 }
 
 static void fsmonitor_refresh_callback(struct index_state *istate, const char *name)
diff --git a/fsmonitor.h b/fsmonitor.h
index 739318ab6d1..7f1794b90b0 100644
--- a/fsmonitor.h
+++ b/fsmonitor.h
@@ -44,6 +44,11 @@ void tweak_fsmonitor(struct index_state *istate);
  */
 void refresh_fsmonitor(struct index_state *istate);
 
+/*
+ * Does the received result contain the "trivial" response?
+ */
+int fsmonitor_is_trivial_response(const struct strbuf *query_result);
+
 /*
  * Set the given cache entries CE_FSMONITOR_VALID bit. This should be
  * called any time the cache entry has been updated to reflect the
-- 
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