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

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Message-ID: <7bcde520-e933-c2d6-c960-3f8acdaf6047@huawei.com>
Date:   Mon, 7 Dec 2020 20:02:20 +0300
From:   Alexei Budankov <abudankov@...wei.com>
To:     Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
CC:     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

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.

Regards,
Alexei