Re: [PATCH 2/3] tracing: Clean up and document pred_funcs_##type creation and use

[Masami Hiramatsu]

On Fri, 09 Mar 2018 21:34:44 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
> 
> The pred_funcs_##type arrays consist of five functions that are assigned
> based on the ops. The array must be in the same order of the ops each
> function represents. The PRED_FUNC_START macro denotes the op enum that
> starts the op that maps to the pred_funcs_##type arrays. This is all very
> subtle and prone to bugs if the code is changed.
> 
> Add comments describing how PRED_FUNC_START and pred_funcs_##type array is
> used, and also a PRED_FUNC_MAX that is the maximum number of functions in
> the arrays.
> 
> Clean up select_comparison_fn() that assigns the predicates to the
> pred_funcs_##type array function as well as add protection in case an op is
> passed in that does not map correctly to the array.
> 

This looks good to me.

Reviewed-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

Thanks,

> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> ---
>  kernel/trace/trace_events_filter.c | 46 ++++++++++++++++++++++++++------------
>  1 file changed, 32 insertions(+), 14 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
> index a2ef393b3bb2..9d383f4383dc 100644
> --- a/kernel/trace/trace_events_filter.c
> +++ b/kernel/trace/trace_events_filter.c
> @@ -65,6 +65,13 @@ struct filter_op {
>  
>  static struct filter_op filter_ops[] = { OPS };
>  
> +/*
> + * pred functions are OP_LT, OP_LE, OP_GT, OP_GE, and OP_BAND
> + * pred_funcs_##type below must match the order of them above.
> + */
> +#define PRED_FUNC_START			OP_LT
> +#define PRED_FUNC_MAX			(OP_BAND - PRED_FUNC_START)
> +
>  #define ERRORS								\
>  	C( NONE,	 	"No error"),				\
>  	C( INVALID_OP,		"Invalid operator"),			\
> @@ -172,8 +179,6 @@ static const filter_pred_fn_t pred_funcs_##type[] = {			\
>  	filter_pred_BAND_##type,					\
>  };
>  
> -#define PRED_FUNC_START			OP_LT
> -
>  #define DEFINE_EQUALITY_PRED(size)					\
>  static int filter_pred_##size(struct filter_pred *pred, void *event)	\
>  {									\
> @@ -946,39 +951,52 @@ static filter_pred_fn_t select_comparison_fn(enum filter_op_ids op,
>  					    int field_size, int field_is_signed)
>  {
>  	filter_pred_fn_t fn = NULL;
> +	int pred_func_index = -1;
> +
> +	switch (op) {
> +	case OP_EQ:
> +	case OP_NE:
> +		break;
> +	default:
> +		if (WARN_ON_ONCE(op < PRED_FUNC_START))
> +			return NULL;
> +		pred_func_index = op - PRED_FUNC_START;
> +		if (WARN_ON_ONCE(pred_func_index > PRED_FUNC_MAX))
> +			return NULL;
> +	}
>  
>  	switch (field_size) {
>  	case 8:
> -		if (op == OP_EQ || op == OP_NE)
> +		if (pred_func_index < 0)
>  			fn = filter_pred_64;
>  		else if (field_is_signed)
> -			fn = pred_funcs_s64[op - PRED_FUNC_START];
> +			fn = pred_funcs_s64[pred_func_index];
>  		else
> -			fn = pred_funcs_u64[op - PRED_FUNC_START];
> +			fn = pred_funcs_u64[pred_func_index];
>  		break;
>  	case 4:
> -		if (op == OP_EQ || op == OP_NE)
> +		if (pred_func_index < 0)
>  			fn = filter_pred_32;
>  		else if (field_is_signed)
> -			fn = pred_funcs_s32[op - PRED_FUNC_START];
> +			fn = pred_funcs_s32[pred_func_index];
>  		else
> -			fn = pred_funcs_u32[op - PRED_FUNC_START];
> +			fn = pred_funcs_u32[pred_func_index];
>  		break;
>  	case 2:
> -		if (op == OP_EQ || op == OP_NE)
> +		if (pred_func_index < 0)
>  			fn = filter_pred_16;
>  		else if (field_is_signed)
> -			fn = pred_funcs_s16[op - PRED_FUNC_START];
> +			fn = pred_funcs_s16[pred_func_index];
>  		else
> -			fn = pred_funcs_u16[op - PRED_FUNC_START];
> +			fn = pred_funcs_u16[pred_func_index];
>  		break;
>  	case 1:
> -		if (op == OP_EQ || op == OP_NE)
> +		if (pred_func_index < 0)
>  			fn = filter_pred_8;
>  		else if (field_is_signed)
> -			fn = pred_funcs_s8[op - PRED_FUNC_START];
> +			fn = pred_funcs_s8[pred_func_index];
>  		else
> -			fn = pred_funcs_u8[op - PRED_FUNC_START];
> +			fn = pred_funcs_u8[pred_func_index];
>  		break;
>  	}
>  
> -- 
> 2.15.1
> 
> 


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>