linux-kernel - Re: [PATCH] tracing user_events: Simplify user_event_parse

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Date: Mon, 8 Jan 2024 21:47:44 +0000
From: Beau Belgrave <beaub@...ux.microsoft.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH] tracing user_events: Simplify user_event_parse_field()
 parsing

On Mon, Jan 08, 2024 at 01:37:23PM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> 
> Instead of having a bunch of if statements with:
> 
>        len = str_has_prefix(field, "__data_loc unsigned ");
>        if (len)
>                goto skip_next;
> 
>        len = str_has_prefix(field, "__data_loc ");
>        if (len)
>                goto skip_next;
> 
>        len = str_has_prefix(field, "__rel_loc unsigned ");
>        if (len)
>                goto skip_next;
> 
>        len = str_has_prefix(field, "__rel_loc ");
>        if (len)
>                goto skip_next;
> 
> 	goto parse;
> 
>  skip_next:
> 
> Consolidate it into a negative check and jump to parse if all the
> str_has_prefix() calls fail. If one succeeds, it will just continue with
> len equal to the proper string:
> 
>        if (!(len = str_has_prefix(field, "__data_loc unsigned ")) &&
>            !(len = str_has_prefix(field, "__data_loc ")) &&
>            !(len = str_has_prefix(field, "__rel_loc unsigned ")) &&
>            !(len = str_has_prefix(field, "__rel_loc "))) {
>                goto parse;
>        }
> 
>  skip_next:
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  kernel/trace/trace_events_user.c | 22 ++++++----------------
>  1 file changed, 6 insertions(+), 16 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> index 9365ce407426..ce0c5f1ded48 100644
> --- a/kernel/trace/trace_events_user.c
> +++ b/kernel/trace/trace_events_user.c
> @@ -1175,23 +1175,13 @@ static int user_event_parse_field(char *field, struct user_event *user,
>  		goto skip_next;
>  	}
>  
> -	len = str_has_prefix(field, "__data_loc unsigned ");
> -	if (len)
> -		goto skip_next;
> -
> -	len = str_has_prefix(field, "__data_loc ");
> -	if (len)
> -		goto skip_next;
> -
> -	len = str_has_prefix(field, "__rel_loc unsigned ");
> -	if (len)
> -		goto skip_next;
> -
> -	len = str_has_prefix(field, "__rel_loc ");
> -	if (len)
> -		goto skip_next;
> +	if (!(len = str_has_prefix(field, "__data_loc unsigned ")) &&
> +	    !(len = str_has_prefix(field, "__data_loc ")) &&
> +	    !(len = str_has_prefix(field, "__rel_loc unsigned ")) &&
> +	    !(len = str_has_prefix(field, "__rel_loc "))) {
> +		goto parse;
> +	}

This now triggers a checkpatch error:
ERROR: do not use assignment in if condition
#1184: FILE: kernel/trace/trace_events_user.c:1184:
+       if (!(len = str_has_prefix(field, "__data_loc unsigned ")) &&

I personally prefer to keep these files fully checkpatch clean.
However, I did test these changes under the self-tests and it passed.

Do they bug you that much? :)

Thanks,
-Beau

>  
> -	goto parse;
>  skip_next:
>  	type = field;
>  	field = strpbrk(field + len, " ");
> -- 
> 2.43.0