From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Carpenter Date: Thu, 27 Nov 2014 15:57:52 +0000 Subject: [patch v2] tracing: truncated output is better than nothing Message-Id: <20141127155752.GA21914@mwanda> List-Id: In-Reply-To: <20141126102244.4bffa4b2@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Steven Rostedt Cc: Ingo Molnar , linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org 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. Signed-off-by: Dan Carpenter diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 42a822d..ab76b7b 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2160,9 +2160,7 @@ __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; @@ -2173,8 +2171,7 @@ __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);