tracepoint event exclusion

Hi,

In order to support situations where a user wants generally all tracepoints enabled but specific tracepoints to be suppressed during a trace session, I created a small patch that allows us to do the following:

...
lttng enable-event -u -c met_tools -a
lttng enable-event -u -c met_tools --tracepoint '!met_func:*' lttng enable-event -u -c met_tools --tracepoint '!met_call:*'

...

This has the effect that all tracepoints get recorded except for tracepoints that match met_func:* or met_call:*.

If you think this feature is useful for others we would be happy to see this patch merged into trunk.

Thanks,
Paul

Signature · 17 lines

Paul Woegerer | SW Development Engineer
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From 74602f6f4ea4b1d7faa01f76542f62b496b94091 Mon Sep 17 00:00:00 2001
From: Paul Woegerer <[email protected]>
Date: Wed, 27 Jun 2012 15:21:30 +0200
Subject: [PATCH] Added excluding/filtering of events with !NAME

---
 liblttng-ust/ltt-events.c |   33 +++++++++++++++++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

liblttng-ust/ltt-events.c +31 -2

index 0fdfd2f..b663312 100644
@@ -150,11 +150,32 @@ struct wildcard_entry *match_wildcard(const struct lttng_event_desc *desc)
 	struct wildcard_entry *e;
 
 	cds_list_for_each_entry(e, &wildcard_list, list) {
+	    size_t len = strlen(e->name);
+	    if (len < 1 || e->name[0] != '!')
+		continue;
+
+	    DBG("Filter %s against wildcard_entry %s\n", desc->name, e->name);
+
+	    /* Compare exclusion wildcards excluding initial '!' and final '*' */
+	    if (!strncmp(desc->name, e->name + 1, len - 2))
+	    {
+		DBG("Exclude %s due to exclusion wildcard_entry %s\n", desc->name, e->name);
+		return NULL; /* exclusion wildcard matched */
+	    }
+	}
+
+	cds_list_for_each_entry(e, &wildcard_list, list) {
+	    size_t len = strlen(e->name);
+	    if (len > 0 && e->name[0] == '!')
+		continue;
+
+	    DBG("Match %s against wildcard_entry %s\n", desc->name, e->name);
+
 		/* If only contain '*' */
-		if (strlen(e->name) == 1)
+		if (len == 1)
 			goto possible_match;
 		/* Compare excluding final '*' */
-		if (!strncmp(desc->name, e->name, strlen(e->name) - 1))
+		if (!strncmp(desc->name, e->name, len - 1))
 			goto possible_match;
 		continue;	/* goto next, no match */
 	possible_match:

@@ -507,6 +528,13 @@ int ltt_event_create(struct ltt_channel *chan,
 	struct ltt_event *event;
 	int ret = 0;
 
+	if (strlen(event_param->name) > 0 && event_param->name[0] == '!')
+	{
+	    struct session_wildcard *sw = NULL;
+	    ltt_wildcard_create(chan, event_param, &sw );
+	    goto filter;
+	}
+
 	if (chan->used_event_id == -1U) {
 		ret = -ENOMEM;
 		goto full;

@@ -607,6 +635,7 @@ cache_error:
 no_loglevel_match:
 exist:
 full:
+filter:
 	return ret;
 }
 

Signature · 7 lines

1.7.10.4


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hrm, although possibly interesting, I don't think this semantic follows the lttng UI event enabling semantic. There are a few use-cases to cover:

1) enable tracepoints, start tracing, run app.

2) enable some tracepoints, start tracing, run app, enable more tracepoints while app is running.

3) start tracing, run app, enable all tracepoints while app is running.

AFAIU, your patch and proposed semantic covers use-case #1, but breaks the other 2. Basically, we have to apply a logical "or" between each enable-event command (rather than an "and" as your proposed semantic suggests), because they can be applied independently.

We could however try to come up with an event attribute that gets applied on a specific event, e.g.:

lttng enable-event -u -a --exclude 'met_func:*' --exclude 'met_call:*'