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Date:   Wed, 6 May 2020 17:21:38 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 02/11] perf evlist: implement control command handling
 functions

Em Wed, May 06, 2020 at 09:19:22PM +0300, Alexey Budankov escreveu:
> 
> Implement functions of initialization, finalization and processing
> of control commands coming from control file descriptors.
> 
> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
> ---
>  tools/perf/util/evlist.c | 100 +++++++++++++++++++++++++++++++++++++++
>  tools/perf/util/evlist.h |  12 +++++
>  2 files changed, 112 insertions(+)
> 
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 2db4bedc4f81..e086c846ef3a 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -1707,3 +1707,103 @@ struct evsel *perf_evlist__reset_weak_group(struct evlist *evsel_list,
>  	}
>  	return leader;
>  }
> +
> +int perf_evlist__initialize_ctlfd(struct evlist *evlist, int ctl_fd, int ctl_fd_ack)
> +{
> +	if (ctl_fd == -1) {
> +		pr_debug("Control descriptor is not initialized\n");
> +		return 0;
> +	}
> +
> +	evlist->ctl_fd_pos = perf_evlist__add_pollfd(&evlist->core, ctl_fd, NULL, POLLIN);
> +	if (evlist->ctl_fd_pos < 0) {
> +		evlist->ctl_fd_pos = -1;
> +		pr_err("Failed to add ctl fd entry: %m\n");
> +		return -1;
> +	}
> +
> +	evlist->ctl_fd = ctl_fd;
> +	evlist->ctl_fd_ack = ctl_fd_ack;
> +
> +	return 0;
> +}
> +
> +int perf_evlist__finalize_ctlfd(struct evlist *evlist)
> +{
> +	if (evlist->ctl_fd_pos == -1)
> +		return 0;
> +
> +	evlist->core.pollfd.entries[evlist->ctl_fd_pos].fd = -1;
> +	evlist->ctl_fd_pos = -1;
> +	evlist->ctl_fd_ack = -1;
> +	evlist->ctl_fd = -1;
> +
> +	return 0;
> +}
> +
> +static int perf_evlist__ctlfd_recv(struct evlist *evlist, enum evlist_ctl_cmd *cmd)
> +{
> +	int err;
> +	char buf[2];
> +
> +	err = read(evlist->ctl_fd, &buf, sizeof(buf));
> +	if (err > 0)
> +		*cmd = buf[0];
> +	else if (err == -1)
> +		pr_err("Failed to read from ctlfd %d: %m\n", evlist->ctl_fd);
> +
> +	return err;
> +}
> +
> +static int perf_evlist__ctlfd_ack(struct evlist *evlist)
> +{
> +	int err;
> +	char buf[2] = {CTL_CMD_ACK, '\n'};
> +
> +	if (evlist->ctl_fd_ack == -1)
> +		return 0;
> +
> +	err = write(evlist->ctl_fd_ack, buf, sizeof(buf));
> +	if (err == -1)
> +		pr_err("failed to write to ctl_ack_fd %d: %m\n", evlist->ctl_fd_ack);
> +
> +	return err;
> +}
> +
> +int perf_evlist__ctlfd_process(struct evlist *evlist, enum evlist_ctl_cmd *cmd)
> +{
> +	int err = 0;
> +	int ctlfd_pos = evlist->ctl_fd_pos;
> +	struct pollfd *entries = evlist->core.pollfd.entries;
> +
> +	if (!entries[ctlfd_pos].revents)
> +		return 0;
> +
> +	if (entries[ctlfd_pos].revents & POLLIN) {
> +		err = perf_evlist__ctlfd_recv(evlist, cmd);
> +		if (err > 0) {
> +			switch (*cmd) {
> +			case CTL_CMD_ENABLE:
> +				evlist__enable(evlist);
> +				break;
> +			case CTL_CMD_DISABLE:
> +				evlist__disable(evlist);
> +				break;
> +			case CTL_CMD_ACK:
> +			case CTL_CMD_UNSUPPORTED:
> +			default:
> +				pr_debug("ctlfd: unsupported %d\n", *cmd);
> +				break;
> +			}
> +			if (!(*cmd == CTL_CMD_ACK || *cmd == CTL_CMD_UNSUPPORTED))
> +				perf_evlist__ctlfd_ack(evlist);
> +		}
> +	}
> +
> +	if (entries[ctlfd_pos].revents & (POLLHUP | POLLERR))
> +		perf_evlist__finalize_ctlfd(evlist);
> +	else
> +		entries[ctlfd_pos].revents = 0;
> +
> +	return err;
> +}
> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> index 62f259d89b41..84386850c290 100644
> --- a/tools/perf/util/evlist.h
> +++ b/tools/perf/util/evlist.h
> @@ -358,4 +358,16 @@ void perf_evlist__force_leader(struct evlist *evlist);
>  struct evsel *perf_evlist__reset_weak_group(struct evlist *evlist,
>  						 struct evsel *evsel,
>  						bool close);
> +
> +enum evlist_ctl_cmd {
> +	CTL_CMD_UNSUPPORTED = 0,
> +	CTL_CMD_ENABLE = 'e',
> +	CTL_CMD_DISABLE = 'd',
> +	CTL_CMD_ACK = 'a'
> +};

Can we make this a string, I think we'll eventually ask for lots more
stuff, like asking for a --switch-output snapshot with --overwrite,
reconfiguring events to increase/decrease frequency, etc, interfacing
with PERF_EVENT_IOC_MODIFY_ATTRIBUTES, PERF_EVENT_IOC_SET_FILTER, etc.

This will also allow us to have parameters, etc, wdyt?

Also please since these are events that deal with 'struct evlist', name
them with the evlist__ prefix, not the perf_evlist__ one, as those
should be used with 'struct perf_evlist', i.e. the one in libperf
(tools/lib/perf/).

Right now this is inconsistent, we did it that way to minimize
disruption of the codebase when moving things from tools/perf/ to
tools/lib/perf/, but this confuses things and I just did a
s/perf_evsel__/evsel__) for things dealing with 'struct evsel', so lets
not add new ones with the wrong prefix, eventually we'll have perf_ only
for things in libperf.

> +
> +int perf_evlist__initialize_ctlfd(struct evlist *evlist, int ctl_fd, int ctl_fd_ack);
> +int perf_evlist__finalize_ctlfd(struct evlist *evlist);
> +int perf_evlist__ctlfd_process(struct evlist *evlist, enum evlist_ctl_cmd *cmd);
> +
>  #endif /* __PERF_EVLIST_H */
> -- 
> 2.24.1
> 
> 

-- 

- Arnaldo

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