linux-kernel - [PATCH 1/2] tracing - trace lost events properly

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Date:	Sat, 12 Mar 2011 23:59:45 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	rostedt@...dmis.org, fweisbec@...il.com, mingo@...hat.com
Cc:	linux-kernel@...r.kernel.org, oleg@...hat.com,
	Jiri Olsa <jolsa@...hat.com>
Subject: [PATCH 1/2] tracing - trace lost events properly

Add proper handling of lost event trace, allowing callers
to get correct trace buffer info.

 - returning TRACE_TYPE_PARTIAL_LINE, in case we dont fit into
   the trace_seq buffer
 - added WARN_ON to make sure we don't miss incorrect trace_seq
   handling

wbr,
jirka


Signed-off-by: Jiri Olsa <jolsa@...hat.com>
---
 kernel/trace/trace.c |   14 +++++++++++---
 1 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 9541c27..20d84f8 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2013,9 +2013,10 @@ enum print_line_t print_trace_line(struct trace_iterator *iter)
 {
 	enum print_line_t ret;
 
-	if (iter->lost_events)
-		trace_seq_printf(&iter->seq, "CPU:%d [LOST %lu EVENTS]\n",
-				 iter->cpu, iter->lost_events);
+	if (iter->lost_events &&
+	    !trace_seq_printf(&iter->seq, "CPU:%d [LOST %lu EVENTS]\n",
+				 iter->cpu, iter->lost_events))
+		return TRACE_TYPE_PARTIAL_LINE;
 
 	if (iter->trace && iter->trace->print_line) {
 		ret = iter->trace->print_line(iter);
@@ -3229,6 +3230,13 @@ waitagain:
 
 		if (iter->seq.len >= cnt)
 			break;
+
+		/*
+		 * Setting the full flag means we reached the trace_seq buffer
+		 * size and we should leave by partial output condition above.
+		 * One of the trace_seq_* functions is not used properly.
+		 */
+		WARN_ON(iter->seq.full);
 	}
 	trace_access_unlock(iter->cpu_file);
 	trace_event_read_unlock();
-- 
1.7.1

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