linux-kernel - Re: [PATCH 2/3] perf tools: Allow to enable/disable events via control file

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Date:   Thu, 10 Dec 2020 21:32:48 +0300
From:   Alexei Budankov <abudankov@...wei.com>
To:     Jiri Olsa <jolsa@...hat.com>
CC:     Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "Namhyung Kim" <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Petlan <mpetlan@...hat.com>,
        Ian Rogers <irogers@...gle.com>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 2/3] perf tools: Allow to enable/disable events via
 control file



On 10.12.2020 21:20, Alexei Budankov wrote:
> 
> On 10.12.2020 21:06, Jiri Olsa wrote:
>> On Thu, Dec 10, 2020 at 05:24:30PM +0100, Jiri Olsa wrote:
>>> On Mon, Dec 07, 2020 at 08:02:20PM +0300, Alexei Budankov wrote:
>>>> Hi,
>>>>
>>>> On 06.12.2020 20:05, Jiri Olsa wrote:
>>>>> Adding new control events to enable/disable specific event.
>>>>> The interface string for control file are:
>>>>>
>>>>>   'enable-<EVENT NAME>'
>>>>>   'disable-<EVENT NAME>'
>>>>
>>>> <SNIP>
>>>>
>>>>>
>>>>> when received the command, perf will scan the current evlist
>>>>> for <EVENT NAME> and if found it's enabled/disabled.
>>>>
>>>> <SNIP>
>>>>
>>>>> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
>>>>> index 70aff26612a9..05723227bebf 100644
>>>>> --- a/tools/perf/util/evlist.c
>>>>> +++ b/tools/perf/util/evlist.c
>>>>> @@ -1915,7 +1915,13 @@ static int evlist__ctlfd_recv(struct evlist *evlist, enum evlist_ctl_cmd *cmd,
>>>>>  		 bytes_read == data_size ? "" : c == '\n' ? "\\n" : "\\0");
>>>>>  
>>>>>  	if (bytes_read > 0) {
>>>>> -		if (!strncmp(cmd_data, EVLIST_CTL_CMD_ENABLE_TAG,
>>>>> +		if (!strncmp(cmd_data, EVLIST_CTL_CMD_ENABLE_EVSEL_TAG,
>>>>> +				    (sizeof(EVLIST_CTL_CMD_ENABLE_EVSEL_TAG)-1))) {
>>>>> +			*cmd = EVLIST_CTL_CMD_ENABLE_EVSEL;
>>>>> +		} else if (!strncmp(cmd_data, EVLIST_CTL_CMD_DISABLE_EVSEL_TAG,
>>>>> +				    (sizeof(EVLIST_CTL_CMD_DISABLE_EVSEL_TAG)-1))) {
>>>>> +			*cmd = EVLIST_CTL_CMD_DISABLE_EVSEL;
>>>>> +		} else if (!strncmp(cmd_data, EVLIST_CTL_CMD_ENABLE_TAG,
>>>>>  			     (sizeof(EVLIST_CTL_CMD_ENABLE_TAG)-1))) {
>>>>>  			*cmd = EVLIST_CTL_CMD_ENABLE;
>>>>>  		} else if (!strncmp(cmd_data, EVLIST_CTL_CMD_DISABLE_TAG,
>>>>> @@ -1952,6 +1958,8 @@ int evlist__ctlfd_process(struct evlist *evlist, enum evlist_ctl_cmd *cmd)
>>>>>  	char cmd_data[EVLIST_CTL_CMD_MAX_LEN];
>>>>>  	int ctlfd_pos = evlist->ctl_fd.pos;
>>>>>  	struct pollfd *entries = evlist->core.pollfd.entries;
>>>>> +	struct evsel *evsel;
>>>>> +	char *evsel_name;
>>>>>  
>>>>>  	if (!evlist__ctlfd_initialized(evlist) || !entries[ctlfd_pos].revents)
>>>>>  		return 0;
>>>>> @@ -1967,6 +1975,26 @@ int evlist__ctlfd_process(struct evlist *evlist, enum evlist_ctl_cmd *cmd)
>>>>>  			case EVLIST_CTL_CMD_DISABLE:
>>>>>  				evlist__disable(evlist);
>>>>>  				break;
>>>>> +			case EVLIST_CTL_CMD_ENABLE_EVSEL:
>>>>> +				evsel_name = cmd_data + sizeof(EVLIST_CTL_CMD_ENABLE_EVSEL_TAG) - 1;
>>>>
>>>> It makes sense to check that evsel_name still points
>>>> into cmd_data buffer after assigning to event name.
>>>
>>> right, will add that
>>
>> actualy it's already checked in evlist__ctlfd_recv, evsel_name at
>> worst will be empty string so evlist__find_evsel_by_str will fail
>>
>> I'll add '' around %s in the error output string:
>>
>>   failed: can't find '%s' event
>>
>> so it's obvious when it's empty

Acked-by: Alexei Budankov <abudankov@...wei.com>

Thanks,
Alexei