Messages in this thread Patch in this message | | | Date | Sat, 18 Mar 2023 15:12:08 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH 1/2] tracing/hist: simplify contains_operator() |
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On Thu, 2 Mar 2023 17:17:54 +0000 Mark Rutland <mark.rutland@arm.com> wrote:
FYI, we follow Linus's preference that subjects start with a capital letter. Unless of course you are a socialist and dislike capitalism?
tracing/hist: Simplify contains_operator()
> In a subsequent patch we'll add additional operators for histogram > expressions.
Refrain from using "subsequent patch", instead say:
Simplify contains_operator() in order to support additional operators for histogram expressions.
> > In preparation for adding additional operators, this patch refactors > contains_operator() to consider each operator within a precedence group > independently by using the 'sep' pointer as the current rightmost > operator, and removing the separate op pointers. > > Within each precedence group, this allows operators to be checked > independently with a consistent pattern: > > op = strrchr(str, $OP_CHAR); > if (op > *sep) { > *sep = op; > field_op = $FIELD_OP_TYPE; > } > > This makes it easy to add new operators of the same precedence without > needing to check multiple pointers, and without needing a final switch > statement to recover the relevant pointer. > > There should be no functional change as a result of this patch. > > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Cc: Masami Hiramatsu <mhiramat@kernel.org> > Cc: Steven Rostedt (Google) <rostedt@goodmis.org> > Cc: Tom Zanussi <zanussi@kernel.org> > Cc: linux-trace-kernel@vger.kernel.org > --- > kernel/trace/trace_events_hist.c | 80 ++++++++++++-------------------- > 1 file changed, 30 insertions(+), 50 deletions(-) > > diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c > index 10d36f751fcd..a308da2cde2f 100644 > --- a/kernel/trace/trace_events_hist.c > +++ b/kernel/trace/trace_events_hist.c > @@ -1813,13 +1813,15 @@ static char *expr_str(struct hist_field *field, unsigned int level) > static int contains_operator(char *str, char **sep) > { > enum field_op_id field_op = FIELD_OP_NONE; > - char *minus_op, *plus_op, *div_op, *mult_op; > + char *op; > > + *sep = NULL;
Hmm!
> > /* > - * Report the last occurrence of the operators first, so that the > - * expression is evaluated left to right. This is important since > - * subtraction and division are not associative. > + * For operators of the same precedence report the last occurrence of > + * the operators first, so that the expression is evaluated left to > + * right. This is important since subtraction and division are not > + * associative. > * > * e.g > * 64/8/4/2 is 1, i.e 64/8/4/2 = ((64/8)/4)/2 > @@ -1830,68 +1832,46 @@ static int contains_operator(char *str, char **sep) > * First, find lower precedence addition and subtraction > * since the expression will be evaluated recursively. > */ > - minus_op = strrchr(str, '-'); > - if (minus_op) { > + op = strrchr(str, '-'); > + if (op > *sep) {
Why compare to *sep if it is always NULL?
Oh! But later in the code we have:
if (contains_operator(field, NULL) || is_var_ref(field))
I wonder how *sep = NULL will handle that?
-- Steve
> + *sep = op; > + > /* > * Unary minus is not supported in sub-expressions. If > * present, it is always the next root operator. > */ > - if (minus_op == str) { > - field_op = FIELD_OP_UNARY_MINUS; > - goto out; > - } > + if (op == str) > + return FIELD_OP_UNARY_MINUS; > > field_op = FIELD_OP_MINUS; > } >
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