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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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