Re: [PATCH v25 10/16] trace-cmd: Add time sync protocol flags

[Steven Rostedt <rostedt@goodmis.org>]

On Thu, 29 Oct 2020 13:18:10 +0200
"Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com> wrote:

> Added 32bit flags for the time synchronization protocols. The first added
> flag is TRACECMD_TSYNC_FLAG_INTERPOLATE, used to specify how the
> timestamps must be corrected.
>  - If the flag is set, an interpolation is performed:
>    Find the (min, max) interval from the offsets array and calculate
> offset specific to the given timestamp using interpolation in that
> interval.
>  - If the flag is not set, do not interpolate:
>    Find the (min, max) interval from the offsets array and use the
>    min offset for all timespamps within the interval.

    "timestamps"

> 
> These flags are set by the timestamp synchronization protocols at the
> protocol initialization time.
> 
> Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
> ---
> --- a/tracecmd/trace-tsync.c
> +++ b/tracecmd/trace-tsync.c
> @@ -132,7 +132,8 @@ out:
>  static void write_guest_time_shift(struct buffer_instance *instance)
>  {
>  	struct tracecmd_output *handle;
> -	struct iovec vector[5];
> +	struct iovec vector[6];
> +	unsigned int flags;
>  	long long *scalings = NULL;
>  	long long *offsets = NULL;
>  	long long *ts = NULL;
> @@ -145,6 +146,9 @@ static void write_guest_time_shift(struct buffer_instance *instance)
>  					 &ts, &offsets, &scalings);
>  	if (ret < 0 || !count || !ts || !offsets || !scalings)
>  		return;
> +	ret = tracecmd_tsync_get_proto_flags(&instance->tsync, &flags);
> +	if (ret < 0)
> +		return;
>  
>  	file = instance->output_file;
>  	fd = open(file, O_RDWR);
> @@ -154,14 +158,16 @@ static void write_guest_time_shift(struct buffer_instance *instance)
>  	vector[0].iov_len = 8;
>  	vector[0].iov_base = &top_instance.trace_id;
>  	vector[1].iov_len = 4;
> -	vector[1].iov_base = &count;
> -	vector[2].iov_len = 8 * count;
> -	vector[2].iov_base = ts;
> +	vector[1].iov_base = &flags;
> +	vector[2].iov_len = 4;
> +	vector[2].iov_base = &count;
>  	vector[3].iov_len = 8 * count;
> -	vector[3].iov_base = offsets;
> +	vector[3].iov_base = ts;
>  	vector[4].iov_len = 8 * count;
> -	vector[4].iov_base = scalings;
> -	tracecmd_add_option_v(handle, TRACECMD_OPTION_TIME_SHIFT, vector, 5);
> +	vector[4].iov_base = offsets;
> +	vector[5].iov_len = 8 * count;
> +	vector[5].iov_base = scalings;
> +	tracecmd_add_option_v(handle, TRACECMD_OPTION_TIME_SHIFT, vector, 6);
>  	tracecmd_append_options(handle);
>  	tracecmd_output_close(handle);
>  #ifdef TSYNC_DEBUG

To make the above cleaner, I would use an enum to define the vector
indexes:

enum {
	VECTOR_TRACE_ID,
	VECTOR_FLAGS,
	VECTOR_COUNT,
	VECTOR_TIMES,
	VECTOR_OFFSETS,
	VECTOR_SCALINGS,
}

And then you can make it:

	vector[VECTOR_TRACE_ID].iov_len = 8;
	vector[VECTOR_TRACE_ID].iov_base = &top_instance.trace_id;
	vector[VECTOR_FLAGS].iov_len = 4;
	vector[VECTOR_FLAGS].iov_base = &flags;
	vector[VECTOR_COUNT].iov_len = 4;
	vector[VECTOR_COUNT].iov_base = &count;
	vector[VECTOR_TIMES].iov_len = 8 * count;
	vector[VECTOR_TIMES].iov_base = ts;
	vector[VECTOR_OFFSETS].iov_len = 8 * count;
	vector[VECTOR_OFFSETS].iov_base = offsets;
	vector[VECTOR_SCALINGS].iov_len = 8 * count;
	vector[VECTOR_SCALINGS].iov_base = scalings;

It makes it obvious what each vector is used for.

This is just an opinion. You don't need to implement it. I just hate
hard coded numbers ;-)

-- Steve