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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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