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tracing: Truncated output is better than nothing

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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>
This commit is contained in:
Dan Carpenter 2014-11-27 18:57:52 +03:00 committed by Steven Rostedt
parent 8e1e1df29d
commit 3558a5ac50
1 changed files with 2 additions and 5 deletions
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7
kernel/trace/trace.c
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@ -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);