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    SubjectRe: [PATCH v2] printk: add console output tracing
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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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