trace2: write discard message to sentinel files

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

Writing this message into the sentinel file is useful for tracking how
often the file count check triggers in practice.

Bump up the event format version since we've added a new event type.

Signed-off-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/technical/api-trace2.txt b/Documentation/technical/api-trace2.txt
index 18b79128fd9c60252d1151f22afac47f796cfaa5..a045dbe422ff000fa29216028a1cfc7c4b071515 100644 (file)
--- 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 +616,23 @@ 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
 }
 ------------
 
+`"discard"`::
+       This event is written to the git-trace2-discard sentinel file if there
+       are too many files in the target trace directory (see the
+       trace2.maxFiles config option).
++
+------------
+{
+       "event":"discard",
+       ...
+}
+------------
+
 `"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 bf75e06e30a7aecf76ac37f35b7d368338bd4020..7065a1b9373b0a02a9b632b00aba2a1c5d5b1465 100755 (executable)
--- a/t/t0212-trace2-event.sh
+++ b/t/t0212-trace2-event.sh
@@ -279,7 +279,9 @@ test_expect_success 'discard traces when there are too many files' '
        ) &&
        echo git-trace2-discard >>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-discard | grep \"event\":\"version\" &&
+       head -n2 trace_target_dir/git-trace2-discard | tail -n1 | grep \"event\":\"too_many_files\"
 '
 
 test_done

diff --git a/trace2/tr2_dst.c b/trace2/tr2_dst.c
index a88c4661002a4677a5399ad732cd7566d50c12da..ae052a07fe2e4d81defdd614c2a025720bbf326b 100644 (file)
--- a/trace2/tr2_dst.c
+++ b/trace2/tr2_dst.c
@@ -48,15 +48,19 @@ 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 there
+ * are too many files 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_too_many_files(const char *tgt_prefix)
+static int tr2_dst_too_many_files(struct tr2_dst *dst, const char *tgt_prefix)
 {
        int file_count = 0, max_files = 0, ret = 0;
        const char *max_files_var;
@@ -95,8 +99,9 @@ static int tr2_dst_too_many_files(const char *tgt_prefix)
                closedir(dirp);
 
        if (file_count >= tr2env_max_files) {
-               creat(sentinel_path.buf, 0666);
-               ret = 1;
+               dst->too_many_files = 1;
+               dst->fd = open(sentinel_path.buf, O_WRONLY | O_CREAT | O_EXCL, 0666);
+               ret = -1;
                goto cleanup;
        }
 
@@ -108,7 +113,7 @@ cleanup:
 
 static int tr2_dst_try_auto_path(struct tr2_dst *dst, const char *tgt_prefix)
 {
-       int fd;
+       int too_many_files;
        const char *last_slash, *sid = tr2_sid_get();
        struct strbuf path = STRBUF_INIT;
        size_t base_path_len;
@@ -124,7 +129,19 @@ 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_too_many_files(tgt_prefix)) {
+       too_many_files = tr2_dst_too_many_files(dst, tgt_prefix);
+       if (!too_many_files) {
+               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 (too_many_files == 1) {
                strbuf_release(&path);
                if (tr2_dst_want_warning())
                        warning("trace2: not opening %s trace file due to too "
@@ -134,18 +151,7 @@ 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,
@@ -159,7 +165,6 @@ 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 3adf3bac139b1aa910b4aea0dc71e3b03ce722ed..b1a8c144e073ba9c5f5d085fa864b5bfb99892fa 100644 (file)
--- 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 too_many_files : 1;
 };
 
 /*

diff --git a/trace2/tr2_tgt_event.c b/trace2/tr2_tgt_event.c
index 9bcac20d1b5a3da6a996c85adbaf4eb19ffb9f15..6353e8ad915610bc93147c5291bc6f31020ac03f 100644 (file)
--- 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_too_many_files_fl(const char *file, int line)
+{
+       const char *event_name = "too_many_files";
+       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.too_many_files)
+               fn_too_many_files_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 438ed05a408e627d1cee0776e22762e10a5e4a3a..31b602c171fc69177a75c62135ed2629b62ec892 100644 (file)
--- 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 fd979db4ad80040ae34dfe1c53816040364e1eb3..ffac8029ad77b66aa9f94612d896ccda9e31ade0 100644 (file)
--- 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>"