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    SubjectRe: [PATCH v2] printk: add console output tracing
    On Thu, Nov 17, 2011 at 04:21:08PM +0100, Johannes Berg wrote:
    > From: Johannes Berg <johannes.berg@intel.com>
    >
    > Add a printk.console trace point to record any printk
    > messages into the trace, regardless of the current
    > console loglevel. This can help correlate (existing)
    > printk debugging with other tracing.
    >
    > Signed-off-by: Johannes Berg <johannes.berg@intel.com>
    > ---
    > v2: remove extra file
    >
    > include/trace/events/printk.h | 44 ++++++++++++++++++++++++++++++++++++++++++
    > kernel/printk.c | 5 ++++
    > 2 files changed, 49 insertions(+)
    >
    > --- /dev/null 1970-01-01 00:00:00.000000000 +0000
    > +++ b/include/trace/events/printk.h 2011-11-16 23:18:35.000000000 +0100
    > @@ -0,0 +1,44 @@
    > +#undef TRACE_SYSTEM
    > +#define TRACE_SYSTEM printk
    > +
    > +#if !defined(_TRACE_PRINTK_H) || defined(TRACE_HEADER_MULTI_READ)
    > +#define _TRACE_PRINTK_H
    > +
    > +#include <linux/tracepoint.h>
    > +
    > +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()

    Thanks.

    > + ),
    > +
    > + TP_fast_assign(
    > + if ((start & (log_buf_len - 1)) > (end & (log_buf_len - 1))) {
    > + memcpy(__get_dynamic_array(msg),
    > + log_buf + (start & (log_buf_len - 1)),
    > + log_buf_len - (start & (log_buf_len - 1)));
    > + memcpy((char *)__get_dynamic_array(msg) +
    > + log_buf_len - (start & (log_buf_len - 1)),
    > + log_buf, end & (log_buf_len - 1));
    > + } else
    > + memcpy(__get_dynamic_array(msg),
    > + log_buf + (start & (log_buf_len - 1)),
    > + (end - start + log_buf_len) & (log_buf_len - 1));
    > + ((char *)__get_dynamic_array(msg))[(end - start + log_buf_len) &
    > + (log_buf_len - 1)] = 0;
    > + ),
    > +
    > + TP_printk("%s", __get_str(msg))
    > +);
    > +#endif /* _TRACE_PRINTK_H */
    > +
    > +/* This part must be outside protection */
    > +#include <trace/define_trace.h>
    > --- a/kernel/printk.c 2011-11-16 22:25:43.000000000 +0100
    > +++ b/kernel/printk.c 2011-11-17 16:19:19.000000000 +0100
    > @@ -44,6 +44,9 @@
    >
    > #include <asm/uaccess.h>
    >
    > +#define CREATE_TRACE_POINTS
    > +#include <trace/events/printk.h>
    > +
    > /*
    > * Architectures can override it:
    > */
    > @@ -542,6 +545,8 @@ MODULE_PARM_DESC(ignore_loglevel, "ignor
    > static void _call_console_drivers(unsigned start,
    > unsigned end, int msg_log_level)
    > {
    > + trace_console(&LOG_BUF(0), start, end, log_buf_len);
    > +
    > if ((msg_log_level < console_loglevel || ignore_loglevel) &&
    > console_drivers && start != end) {
    > if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
    >
    >


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