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    Subject[PATCH v2] printk: add console output tracing
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    Date
    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)
    + ),
    +
    + 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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