linux-kernel - Re: [PATCH 2/7] tracing: Change strlen to sizeof for hist trigger static strings

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Date:   Wed, 19 Dec 2018 13:46:49 -0600
From:   Tom Zanussi <zanussi@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     tglx@...utronix.de, mhiramat@...nel.org, namhyung@...nel.org,
        vedang.patel@...el.com, bigeasy@...utronix.de,
        joel@...lfernandes.org, mathieu.desnoyers@...icios.com,
        julia@...com, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org
Subject: Re: [PATCH 2/7] tracing: Change strlen to sizeof for hist trigger
 static strings

Hi Steve,

On Wed, 2018-12-19 at 14:40 -0500, Steven Rostedt wrote:
> On Tue, 18 Dec 2018 14:33:21 -0600
> Tom Zanussi <zanussi@...nel.org> wrote:
> 
> > From: Tom Zanussi <tom.zanussi@...ux.intel.com>
> > 
> > There's no need to use strlen() for static strings when the length
> > is
> > already known, so update trace_events_hist.c with sizeof() for
> > those
> > cases.
> > 
> > Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
> > ---
> >  kernel/trace/trace_events_hist.c | 38 +++++++++++++++++++---------
> > ----------
> >  1 file changed, 19 insertions(+), 19 deletions(-)
> > 
> > diff --git a/kernel/trace/trace_events_hist.c
> > b/kernel/trace/trace_events_hist.c
> > index d29bf8a8e1dd..25d06b3ae1f6 100644
> > --- a/kernel/trace/trace_events_hist.c
> > +++ b/kernel/trace/trace_events_hist.c
> > @@ -507,7 +507,7 @@ static int synth_field_string_size(char *type)
> >  	start = strstr(type, "char[");
> >  	if (start == NULL)
> >  		return -EINVAL;
> > -	start += strlen("char[");
> > +	start += sizeof("char[") - 1;
> >  
> >  	end = strchr(type, ']');
> >  	if (!end || end < start)
> > @@ -1843,8 +1843,8 @@ static int parse_action(char *str, struct
> > hist_trigger_attrs *attrs)
> >  	if (attrs->n_actions >= HIST_ACTIONS_MAX)
> >  		return ret;
> >  
> > -	if ((strncmp(str, "onmatch(", strlen("onmatch(")) == 0) ||
> > -	    (strncmp(str, "onmax(", strlen("onmax(")) == 0)) {
> > +	if ((strncmp(str, "onmatch(", sizeof("onmatch(") - 1) ==
> > 0) ||
> > +	    (strncmp(str, "onmax(", sizeof("onmax(") - 1) == 0)) {
> >  		attrs->action_str[attrs->n_actions] = kstrdup(str,
> > GFP_KERNEL);
> >  		if (!attrs->action_str[attrs->n_actions]) {
> >  			ret = -ENOMEM;
> > @@ -1861,34 +1861,34 @@ static int parse_assignment(char *str,
> > struct hist_trigger_attrs *attrs)
> >  {
> >  	int ret = 0;
> >  
> > -	if ((strncmp(str, "key=", strlen("key=")) == 0) ||
> > -	    (strncmp(str, "keys=", strlen("keys=")) == 0)) {
> > +	if ((strncmp(str, "key=", sizeof("key=") - 1) == 0) ||
> > +	    (strncmp(str, "keys=", sizeof("keys=") - 1) == 0)) {
> >  		attrs->keys_str = kstrdup(str, GFP_KERNEL);
> 
> I'll apply this as is, but since there's a lot of these, I wonder if
> we
> should make a marcro for this:
> 
> #define strcmp_const(str, str_const) strncmp(str, str_const,
> sizeof(str_const) - 1)
> 
> ?
> 
> This would help prevent bugs due to typos and bad cut and paste.
> 

Yeah, I had considered it but wasn't sure it was worth it.  Since
you're suggesting it is, I can send another patch on top of these, or
feel free if you want to too.  ;-)

Tom