linux-kernel - Re: [PATCH v5 06/21] perf arm-spe: Refactor printing string to buffer

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Date:   Thu, 29 Oct 2020 10:54:37 +0000
From:   André Przywara <andre.przywara@....com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Dave Martin <Dave.Martin@....com>,
        Wei Li <liwei391@...wei.com>,
        James Clark <james.clark@....com>, Al Grant <Al.Grant@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 06/21] perf arm-spe: Refactor printing string to buffer

On 29/10/2020 10:51, Leo Yan wrote:
> Hi Andre,
> 
> On Thu, Oct 29, 2020 at 10:23:39AM +0000, Andrï¿½ Przywara wrote:
> 
> [...]
> 
>>> +static int arm_spe_pkt_snprintf(int *err, char **buf_p, size_t *blen,
>>> +				const char *fmt, ...)
>>> +{
>>> +	va_list ap;
>>> +	int ret;
>>> +
>>> +	va_start(ap, fmt);
>>> +	ret = vsnprintf(*buf_p, *blen, fmt, ap);
>>> +	va_end(ap);
>>> +
>>> +	if (ret < 0) {
>>> +		if (err && !*err)
>>> +			*err = ret;
>>> +	} else {
>>> +		*buf_p += ret;
>>> +		*blen -= ret;
>>> +	}
>>> +
>>> +	return ret;
>>> +}
>>
>> So this now implements the old behaviour of ignoring previous errors, in
>> all cases, since we don't check for errors and bail out in the callers.
>>
>> If you simply check for validity of err and for it being 0 before
>> proceeding with the va_start() above, this should be fixed.
> 
> I think you are suggesting below code, could you take a look for it
> before I proceed to respin new patch?>
> static int arm_spe_pkt_snprintf(int *err, char **buf_p, size_t *blen,
> 				const char *fmt, ...)
> {
> 	va_list ap;
> 	int ret;
> 
>         /* Bail out if any error occurred */
>         if (err && *err)
>                 return *err;
> 
> 	va_start(ap, fmt);
> 	ret = vsnprintf(*buf_p, *blen, fmt, ap);
> 	va_end(ap);
> 
> 	if (ret < 0) {
> 		if (err && !*err)
> 			*err = ret;
> 	} else {
> 		*buf_p += ret;
> 		*blen -= ret;
> 	}
> 
> 	return ret;
> }

Yes, this is what I had in mind.

Cheers,
Andre