Re: [RFC PATCH 2/4] vfio-ccw: Trace the FSM jumptable

[Steffen Maier <maier@linux.ibm.com>]

On 10/14/19 8:08 PM, Eric Farman wrote:
> It would be nice if we could track the sequence of events within
> vfio-ccw, based on the state of the device/FSM and our calling
> sequence within it.  So let's add a simple trace here so we can
> watch the states change as things go, and allow it to be folded
> into the rest of the other cio traces.
> 
> Signed-off-by: Eric Farman <farman@linux.ibm.com>
> ---
>   drivers/s390/cio/vfio_ccw_private.h |  1 +
>   drivers/s390/cio/vfio_ccw_trace.c   |  1 +
>   drivers/s390/cio/vfio_ccw_trace.h   | 26 ++++++++++++++++++++++++++
>   3 files changed, 28 insertions(+)
> 
> diff --git a/drivers/s390/cio/vfio_ccw_private.h b/drivers/s390/cio/vfio_ccw_private.h
> index bbe9babf767b..9b9bb4982972 100644
> --- a/drivers/s390/cio/vfio_ccw_private.h
> +++ b/drivers/s390/cio/vfio_ccw_private.h
> @@ -135,6 +135,7 @@ extern fsm_func_t *vfio_ccw_jumptable[NR_VFIO_CCW_STATES][NR_VFIO_CCW_EVENTS];
>   static inline void vfio_ccw_fsm_event(struct vfio_ccw_private *private,
>   				     int event)
>   {
> +	trace_vfio_ccw_fsm_event(private->sch->schid, private->state, event);
>   	vfio_ccw_jumptable[private->state][event](private, event);
>   }
> 
> diff --git a/drivers/s390/cio/vfio_ccw_trace.c b/drivers/s390/cio/vfio_ccw_trace.c
> index d5cc943c6864..b37bc68e7f18 100644
> --- a/drivers/s390/cio/vfio_ccw_trace.c
> +++ b/drivers/s390/cio/vfio_ccw_trace.c
> @@ -9,4 +9,5 @@
>   #define CREATE_TRACE_POINTS
>   #include "vfio_ccw_trace.h"
> 
> +EXPORT_TRACEPOINT_SYMBOL(vfio_ccw_fsm_event);
>   EXPORT_TRACEPOINT_SYMBOL(vfio_ccw_io_fctl);
> diff --git a/drivers/s390/cio/vfio_ccw_trace.h b/drivers/s390/cio/vfio_ccw_trace.h
> index 2a2937a40124..24a8152acfdf 100644
> --- a/drivers/s390/cio/vfio_ccw_trace.h
> +++ b/drivers/s390/cio/vfio_ccw_trace.h
> @@ -17,6 +17,32 @@
> 
>   #include <linux/tracepoint.h>
> 
> +TRACE_EVENT(vfio_ccw_fsm_event,
> +	TP_PROTO(struct subchannel_id schid, int state, int event),
> +	TP_ARGS(schid, state, event),
> +
> +	TP_STRUCT__entry(
> +		__field(u8, cssid)
> +		__field(u8, ssid)
> +		__field(u16, schno)
> +		__field(int, state)
> +		__field(int, event)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->cssid = schid.cssid;
> +		__entry->ssid = schid.ssid;
> +		__entry->schno = schid.sch_no;
> +		__entry->state = state;
> +		__entry->event = event;
> +	),
> +
> +	TP_printk("schid=%x.%x.%04x state=%x event=%x",

/sys/kernel/debug/tracing/events](0)# grep -R '%[^%]*x'

Many existing TPs often seem to format hex output with a 0x prefix (either 
explicit with 0x%x or implicit with %#x). Since some of your other TPs also 
output decimal integer values, I wonder if a distinction would help 
unexperienced TP readers.

> +		__entry->cssid, __entry->ssid, __entry->schno,
> +		__entry->state,
> +		__entry->event)
> +);
> +
>   TRACE_EVENT(vfio_ccw_io_fctl,
>   	TP_PROTO(int fctl, struct subchannel_id schid, int errno, char *errstr),
>   	TP_ARGS(fctl, schid, errno, errstr),
> 


-- 
Mit freundlichen Gruessen / Kind regards
Steffen Maier

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