Commit 3558a5ac authored Nov 27, 2014 by Dan Carpenter Committed by Steven Rostedt Dec 03, 2014

tracing: Truncated output is better than nothing

The initial reason for this patch is that I noticed that:

	if (len > TRACE_BUF_SIZE)

is off by one.  In this code, if len == TRACE_BUF_SIZE, then it means we
have truncated the last character off the output string.  If we truncate
two or more characters then we exit without printing.

After some discussion, we decided that printing truncated data is better
than not printing at all so we should just use vscnprintf() and remove
the test entirely.  Also I have updated memcpy() to copy the NUL char
instead of setting the NUL in a separate step.

Link: http://lkml.kernel.org/r/20141127155752.GA21914@mwanda



Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

parent 8e1e1df2

kernel/trace/trace.c

+2 −5

Original line number	Diff line number	Diff line
		@@ -2158,9 +2158,7 @@ __trace_array_vprintk(struct ring_buffer *buffer,
		goto out;
		}

		len = vsnprintf(tbuffer, TRACE_BUF_SIZE, fmt, args);
		if (len > TRACE_BUF_SIZE)
		goto out;
		len = vscnprintf(tbuffer, TRACE_BUF_SIZE, fmt, args);

		local_save_flags(flags);
		size = sizeof(*entry) + len + 1;
		@@ -2171,8 +2169,7 @@ __trace_array_vprintk(struct ring_buffer *buffer,
		entry = ring_buffer_event_data(event);
		entry->ip = ip;

		memcpy(&entry->buf, tbuffer, len);
		entry->buf[len] = '\0';
		memcpy(&entry->buf, tbuffer, len + 1);
		if (!call_filter_check_discard(call, entry, buffer, event)) {
		__buffer_unlock_commit(buffer, event);
		ftrace_trace_stack(buffer, flags, 6, pc);

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