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Subject[PATCH 1/3 v4] Add tracing_off_event() to stop tracing when a bug or warning occur
Date
The tracing_off_event() function calls tracing_off() to stop tracing
when an event occurs. By default, only BUG-type events stop tracing,
while WARNING type events do not. This is controlled through the
tracing_off={none,warn,bug} commandline parameter.
Call this function from bug and warning event handlers to enable a user
to debug their kernel by starting a trace, hitting an event, and then
retrieving trace info knowing that the trace was stopped right after the
event was hit.

Signed-off-by: Chase Douglas <chase.douglas@canonical.com>
---
include/linux/kernel.h | 7 +++++++
kernel/trace/ring_buffer.c | 34 ++++++++++++++++++++++++++++++++++
2 files changed, 41 insertions(+), 0 deletions(-)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 9365227..80c67ad 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -478,16 +478,23 @@ static inline char *pack_hex_byte(char *buf, u8 byte)
*
* Most likely, you want to use tracing_on/tracing_off.
*/
+enum trace_off_event {
+ TRACE_EVENT_BUG = 0,
+ TRACE_EVENT_WARN,
+};
+
#ifdef CONFIG_RING_BUFFER
void tracing_on(void);
void tracing_off(void);
/* trace_off_permanent stops recording with no way to bring it back */
void tracing_off_permanent(void);
+void tracing_off_event(enum trace_off_event event);
int tracing_is_on(void);
#else
static inline void tracing_on(void) { }
static inline void tracing_off(void) { }
static inline void tracing_off_permanent(void) { }
+static inline void tracing_off_event(enum trace_off_event event) { }
static inline int tracing_is_on(void) { return 0; }
#endif
#ifdef CONFIG_TRACING
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 41ca394..f6be195 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -194,6 +194,40 @@ void tracing_off_permanent(void)
set_bit(RB_BUFFERS_DISABLED_BIT, &ring_buffer_flags);
}

+static enum trace_off_event tracing_off_event_ctrl = TRACE_EVENT_BUG;
+
+/**
+ * tracing_off_event - turn off tracing depending on event type
+ * @event: type of event that occurred
+ *
+ * This function checks the event type to determine whether tracing should be
+ * disabled. Useful for disabling tracing on bugs or warnings.
+ */
+void tracing_off_event(enum trace_off_event event)
+{
+ if (event <= tracing_off_event_ctrl)
+ tracing_off();
+}
+EXPORT_SYMBOL_GPL(tracing_off_event);
+
+static int __init tracing_off_event_setup(char *str)
+{
+ if (!strcmp("none", str))
+ tracing_off_event_ctrl = -1;
+ else if (!strcmp("bug", str))
+ tracing_off_event_ctrl = TRACE_EVENT_BUG;
+ else if (!strcmp("warn", str))
+ tracing_off_event_ctrl = TRACE_EVENT_WARN;
+ else {
+ printk(KERN_NOTICE "Invalid value passed for tracing_off parameter\n");
+ return 1;
+ }
+
+ return 0;
+}
+
+__setup("tracing_off=", tracing_off_event_setup);
+
/**
* tracing_is_on - show state of ring buffers enabled
*/
--
1.7.0


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