Messages in this thread | | | Subject | Re: [PATCH v2] printk: add console output tracing | From | Johannes Berg <> | Date | Fri, 18 Nov 2011 19:59:12 +0100 |
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On Fri, 2011-11-18 at 19:54 +0100, Frederic Weisbecker wrote: > On Fri, Nov 18, 2011 at 07:46:15PM +0100, Johannes Berg wrote: > > On Fri, 2011-11-18 at 19:44 +0100, Frederic Weisbecker wrote: > > > > > > +TRACE_EVENT_CONDITION(console, > > > > + TP_PROTO(const char *log_buf, unsigned start, unsigned end, > > > > + unsigned log_buf_len), > > > > + > > > > + TP_ARGS(log_buf, start, end, log_buf_len), > > > > + > > > > + TP_CONDITION(start != end), > > > > + > > > > + TP_STRUCT__entry( > > > > + __dynamic_array(char, msg, > > > > + ((end - start + log_buf_len) & > > > > + (log_buf_len - 1)) + 1) > > > > > > Is all that care about log_buf_len necessary? It seems that > > > printk ensures that log_end - con_start never exceeds log_buf_len, > > > looking at emit_log_char() > > > > I think it is. The buffer can wrap around so in that case end < start, > > which just end-start won't handle here. > > Even if it wraps, end - start should always give a positive result. > > We have that check in call_console_drivers(): > > BUG_ON(((int)(start - end)) > 0)
That's .. confusing, start - end > 0 <=> start > end ??
Also, call_console_drivers() doesn't pass this start/end through to _call_console_drivers(), it has loops and stuff there...
In any case -- feel free to clean it all up, I basically copied the logic from _call_console_drivers assuming it was needed. I don't really want to know about the printk details :-)
johannes
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