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[PATCH v4 4/4] trace2: write overload message to sentinel files

From
Josh Steadmon <steadmon@google.com>
Date
Oct 3, 2019, 23:32 UTC
Message-ID
<790c5ac95a8aa929f061fc68c89f53f95778e0f6.1570144820.git.steadmon@google.com>
In-Reply-To
<cover.1570144820.git.steadmon@google.com>

Add a new "overload" event type for trace2 event destinations. When the trace2 overload feature creates a sentinel file, it will include the normal trace2 output in the sentinel, along with this new overload event.

Writing this message into the sentinel file is useful for tracking how often the overload protection feature is triggered in practice.

Bump up the event format version since we've added a new event type.
Signed-off-by: Josh Steadmon <steadmon@google.com>
---
 Documentation/technical/api-trace2.txt | 15 ++++++--
 t/t0212-trace2-event.sh                |  4 ++-
 trace2/tr2_dst.c                       | 47 ++++++++++++++------------
 trace2/tr2_dst.h                       |  1 +
 trace2/tr2_tgt_event.c                 | 31 +++++++++++++----
 trace2/tr2_tgt_normal.c                |  2 +-
 trace2/tr2_tgt_perf.c                  |  2 +-
 7 files changed, 69 insertions(+), 33 deletions(-)
diff --git a/Documentation/technical/api-trace2.txt b/Documentation/technical/api-trace2.txt
index 18b79128fd..5afd643fa6 100644
--- a/Documentation/technical/api-trace2.txt
+++ b/Documentation/technical/api-trace2.txt
@@ -128,7 +128,7 @@ yields
 
 ------------
 $ cat ~/log.event
-{"event":"version","sid":"sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.620713Z","file":"common-main.c","line":38,"evt":"1","exe":"2.20.1.155.g426c96fcdb"}
+{"event":"version","sid":"sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.620713Z","file":"common-main.c","line":38,"evt":"2","exe":"2.20.1.155.g426c96fcdb"}
 {"event":"start","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621027Z","file":"common-main.c","line":39,"t_abs":0.001173,"argv":["git","version"]}
 {"event":"cmd_name","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621122Z","file":"git.c","line":432,"name":"version","hierarchy":"version"}
 {"event":"exit","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621236Z","file":"git.c","line":662,"t_abs":0.001227,"code":0}
@@ -616,11 +616,22 @@ only present on the "start" and "atexit" events.
 {
 	"event":"version",
 	...
-	"evt":"1",		       # EVENT format version
+	"evt":"2",		       # EVENT format version
 	"exe":"2.20.1.155.g426c96fcdb" # git version
 }
 ------------
 
+`"overload"`::
+	This event is created in a sentinel file if we are overloading a target
+	trace directory (see the trace2.maxFiles config option).
++
+------------
+{
+	"event":"overload",
+	...
+}
+------------
+
 `"start"`::
 	This event contains the complete argv received by main().
 +
diff --git a/t/t0212-trace2-event.sh b/t/t0212-trace2-event.sh
index 2ff97e72da..7081153a11 100755
--- a/t/t0212-trace2-event.sh
+++ b/t/t0212-trace2-event.sh
@@ -279,7 +279,9 @@ test_expect_success "don't overload target directory" '
 	) &&
 	echo git-trace2-overload >>expected_filenames.txt &&
 	ls trace_target_dir >ls_output.txt &&
-	test_cmp expected_filenames.txt ls_output.txt
+	test_cmp expected_filenames.txt ls_output.txt &&
+	head -n1 trace_target_dir/git-trace2-overload | grep \"event\":\"version\" &&
+	head -n2 trace_target_dir/git-trace2-overload | tail -n1 | grep \"event\":\"overload\"
 '
 
 test_done
diff --git a/trace2/tr2_dst.c b/trace2/tr2_dst.c
index af3405f179..eedc5a332f 100644
--- a/trace2/tr2_dst.c
+++ b/trace2/tr2_dst.c
@@ -50,15 +50,19 @@ void tr2_dst_trace_disable(struct tr2_dst *dst)
 /*
  * Check to make sure we're not overloading the target directory with too many
  * files. First get the threshold (if present) from the config or envvar. If
- * it's zero or unset, disable this check.  Next check for the presence of a
- * sentinel file, then check file count. If we are overloaded, create the
- * sentinel file if it doesn't already exist.
+ * it's zero or unset, disable this check. Next check for the presence of a
+ * sentinel file, then check file count.
+ *
+ * Returns 0 if tracing should proceed as normal. Returns 1 if the sentinel file
+ * already exists, which means tracing should be disabled. Returns -1 if we are
+ * overloaded but there was no sentinel file, which means we have created and
+ * should write traces to the sentinel file.
  *
  * We expect that some trace processing system is gradually collecting files
  * from the target directory; after it removes the sentinel file we'll start
  * writing traces again.
  */
-static int tr2_dst_overloaded(const char *tgt_prefix)
+static int tr2_dst_overloaded(struct tr2_dst *dst, const char *tgt_prefix)
 {
 	int file_count = 0, max_files = 0, ret = 0;
 	const char *max_files_var;
@@ -97,8 +101,9 @@ static int tr2_dst_overloaded(const char *tgt_prefix)
 		closedir(dirp);
 
 	if (file_count >= tr2env_max_files) {
-		creat(sentinel_path.buf, 0666);
-		ret = 1;
+		dst->overloaded = 1;
+		dst->fd = open(sentinel_path.buf, O_WRONLY | O_CREAT | O_EXCL, 0666);
+		ret = -1;
 		goto cleanup;
 	}
 
@@ -110,7 +115,7 @@ static int tr2_dst_overloaded(const char *tgt_prefix)
 
 static int tr2_dst_try_auto_path(struct tr2_dst *dst, const char *tgt_prefix)
 {
-	int fd;
+	int overloaded;
 	const char *last_slash, *sid = tr2_sid_get();
 	struct strbuf path = STRBUF_INIT;
 	size_t base_path_len;
@@ -126,7 +131,19 @@ static int tr2_dst_try_auto_path(struct tr2_dst *dst, const char *tgt_prefix)
 	strbuf_addstr(&path, sid);
 	base_path_len = path.len;
 
-	if (tr2_dst_overloaded(tgt_prefix)) {
+	overloaded = tr2_dst_overloaded(dst, tgt_prefix);
+	if (!overloaded) {
+		for (attempt_count = 0; attempt_count < MAX_AUTO_ATTEMPTS; attempt_count++) {
+			if (attempt_count > 0) {
+				strbuf_setlen(&path, base_path_len);
+				strbuf_addf(&path, ".%d", attempt_count);
+			}
+
+			dst->fd = open(path.buf, O_WRONLY | O_CREAT | O_EXCL, 0666);
+			if (dst->fd != -1)
+				break;
+		}
+	} else if (overloaded == 1) {
 		strbuf_release(&path);
 		if (tr2_dst_want_warning())
 			warning("trace2: not opening %s trace file due to too "
@@ -136,18 +153,7 @@ static int tr2_dst_try_auto_path(struct tr2_dst *dst, const char *tgt_prefix)
 		return 0;
 	}
 
-	for (attempt_count = 0; attempt_count < MAX_AUTO_ATTEMPTS; attempt_count++) {
-		if (attempt_count > 0) {
-			strbuf_setlen(&path, base_path_len);
-			strbuf_addf(&path, ".%d", attempt_count);
-		}
-
-		fd = open(path.buf, O_WRONLY | O_CREAT | O_EXCL, 0666);
-		if (fd != -1)
-			break;
-	}
-
-	if (fd == -1) {
+	if (dst->fd == -1) {
 		if (tr2_dst_want_warning())
 			warning("trace2: could not open '%.*s' for '%s' tracing: %s",
 				(int) base_path_len, path.buf,
@@ -161,7 +167,6 @@ static int tr2_dst_try_auto_path(struct tr2_dst *dst, const char *tgt_prefix)
 
 	strbuf_release(&path);
 
-	dst->fd = fd;
 	dst->need_close = 1;
 	dst->initialized = 1;
 
diff --git a/trace2/tr2_dst.h b/trace2/tr2_dst.h
index 3adf3bac13..e8abe1e490 100644
--- a/trace2/tr2_dst.h
+++ b/trace2/tr2_dst.h
@@ -9,6 +9,7 @@ struct tr2_dst {
 	int fd;
 	unsigned int initialized : 1;
 	unsigned int need_close : 1;
+	unsigned int overloaded : 1;
 };
 
 /*
diff --git a/trace2/tr2_tgt_event.c b/trace2/tr2_tgt_event.c
index c2852d1bd2..f27bc572c5 100644
--- a/trace2/tr2_tgt_event.c
+++ b/trace2/tr2_tgt_event.c
@@ -10,16 +10,17 @@
 #include "trace2/tr2_tgt.h"
 #include "trace2/tr2_tls.h"
 
-static struct tr2_dst tr2dst_event = { TR2_SYSENV_EVENT, 0, 0, 0 };
+static struct tr2_dst tr2dst_event = { TR2_SYSENV_EVENT, 0, 0, 0, 0 };
 
 /*
- * The version number of the JSON data generated by the EVENT target
- * in this source file.  Update this if you make a significant change
- * to the JSON fields or message structure.  You probably do not need
- * to update this if you just add another call to one of the existing
- * TRACE2 API methods.
+ * The version number of the JSON data generated by the EVENT target in this
+ * source file. The version should be incremented if new event types are added,
+ * if existing fields are removed, or if there are significant changes in
+ * interpretation of existing events or fields. Smaller changes, such as adding
+ * a new field to an existing event, do not require an increment to the EVENT
+ * format version.
  */
-#define TR2_EVENT_VERSION "1"
+#define TR2_EVENT_VERSION "2"
 
 /*
  * Region nesting limit for messages written to the event target.
@@ -107,6 +108,19 @@ static void event_fmt_prepare(const char *event_name, const char *file,
 		jw_object_intmax(jw, "repo", repo->trace2_repo_id);
 }
 
+static void fn_overload_fl(const char *file, int line)
+{
+	const char *event_name = "overload";
+	struct json_writer jw = JSON_WRITER_INIT;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
 static void fn_version_fl(const char *file, int line)
 {
 	const char *event_name = "version";
@@ -120,6 +134,9 @@ static void fn_version_fl(const char *file, int line)
 
 	tr2_dst_write_line(&tr2dst_event, &jw.json);
 	jw_release(&jw);
+
+	if (tr2dst_event.overloaded)
+		fn_overload_fl(file, line);
 }
 
 static void fn_start_fl(const char *file, int line,
diff --git a/trace2/tr2_tgt_normal.c b/trace2/tr2_tgt_normal.c
index 00b116d797..e91633468d 100644
--- a/trace2/tr2_tgt_normal.c
+++ b/trace2/tr2_tgt_normal.c
@@ -9,7 +9,7 @@
 #include "trace2/tr2_tgt.h"
 #include "trace2/tr2_tls.h"
 
-static struct tr2_dst tr2dst_normal = { TR2_SYSENV_NORMAL, 0, 0, 0 };
+static struct tr2_dst tr2dst_normal = { TR2_SYSENV_NORMAL, 0, 0, 0, 0 };
 
 /*
  * Use the TR2_SYSENV_NORMAL_BRIEF setting to omit the "<time> <file>:<line>"
diff --git a/trace2/tr2_tgt_perf.c b/trace2/tr2_tgt_perf.c
index ea0cbbe13e..bebac4782d 100644
--- a/trace2/tr2_tgt_perf.c
+++ b/trace2/tr2_tgt_perf.c
@@ -11,7 +11,7 @@
 #include "trace2/tr2_tgt.h"
 #include "trace2/tr2_tls.h"
 
-static struct tr2_dst tr2dst_perf = { TR2_SYSENV_PERF, 0, 0, 0 };
+static struct tr2_dst tr2dst_perf = { TR2_SYSENV_PERF, 0, 0, 0, 0 };
 
 /*
  * Use TR2_SYSENV_PERF_BRIEF to omit the "<time> <file>:<line>"

-- 
2.23.0.581.g78d2f28ef7-goog
Previous: Josh SteadmonNext: Josh Steadmon
Message 35 of 40 in “trace2: don't overload target directories”
  1. trace2: don't overload target directoriesJosh Steadmon, Jul 29, 2019
  2. Derrick StoleeJul 30, 2019
  3. Josh SteadmonJul 30, 2019
  4. Jeff HostetlerJul 30, 2019
  5. Josh SteadmonJul 30, 2019
  6. Josh SteadmonJul 30, 2019
  7. Jeff HostetlerJul 30, 2019
  8. Josh SteadmonJul 30, 2019
  9. 0/2 trace2: don't overload target directoriesJosh Steadmon, Aug 2, 2019
  10. 1/2 docs: mention trace2 target-dir mode in git-configJosh Steadmon, Aug 2, 2019
  11. 2/2 trace2: don't overload target directoriesJosh Steadmon, Aug 2, 2019
  12. Jeff HostetlerAug 5, 2019
  13. Josh SteadmonAug 5, 2019
  14. SZEDER GáborAug 5, 2019
  15. Josh SteadmonAug 5, 2019
  16. 0/3 trace2: don't overload target directoriesJosh Steadmon, Sep 14, 2019
  17. 1/3 docs: mention trace2 target-dir mode in git-configJosh Steadmon, Sep 14, 2019
  18. 2/3 trace2: don't overload target directoriesJosh Steadmon, Sep 14, 2019
  19. 3/3 trace2: write overload message to sentinel filesJosh Steadmon, Sep 14, 2019
  20. Derrick StoleeSep 16, 2019
  21. Jeff HostetlerSep 16, 2019
  22. Josh SteadmonSep 16, 2019
  23. Jeff HostetlerSep 19, 2019
  24. Josh SteadmonSep 19, 2019
  25. Jeff HostetlerSep 20, 2019
  26. Josh SteadmonSep 16, 2019
  27. 0/4 trace2: don't overload target directoriesJosh Steadmon, Oct 3, 2019
  28. 1/4 docs: mention trace2 target-dir mode in git-configJosh Steadmon, Oct 3, 2019
  29. 2/4 docs: clarify trace2 version invariantsJosh Steadmon, Oct 3, 2019
  30. 3/4 trace2: don't overload target directoriesJosh Steadmon, Oct 3, 2019
  31. Junio C HamanoOct 4, 2019
  32. Josh SteadmonOct 4, 2019
  33. Johannes SchindelinOct 4, 2019
  34. Josh SteadmonOct 4, 2019
  35. 4/4 trace2: write overload message to sentinel filesJosh Steadmon, Oct 3, 2019
  36. 0/4 trace2: discard new traces if the target directory contains too many filesJosh Steadmon, Oct 4, 2019
  37. 1/4 docs: mention trace2 target-dir mode in git-configJosh Steadmon, Oct 4, 2019
  38. 2/4 docs: clarify trace2 version invariantsJosh Steadmon, Oct 4, 2019
  39. 3/4 trace2: discard new traces if target directory has too many filesJosh Steadmon, Oct 4, 2019
  40. 4/4 trace2: write discard message to sentinel filesJosh Steadmon, Oct 4, 2019

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