perf tools: Add 'ping' control command

Add a control 'ping' command to detect if perf is up and its control
interface is operational.

It will be used in following daemon patches to synchronize with record
session - when control interface is up and running, we know that perf
record is monitoring and ready to receive signals.

Example session:

  terminal 1:

    # mkfifo control ack
    # perf record --control=fifo:control,ack

  terminal 2:

    # echo ping > control
    # cat ack
    ack
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexei Budankov <abudankov@huawei.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20201226232038.390883-5-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-record.txt

@@ -652,6 +652,7 @@ Available commands:
   'disable name'     : disable event 'name'
   'snapshot'         : AUX area tracing snapshot).
   'stop'             : stop perf record
+  'ping'             : ping
 
   'evlist [-v|-g|-F] : display all events
                        -F  Show just the sample frequency used for each event.

tools/perf/builtin-record.c

@@ -1950,6 +1950,7 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
 			case EVLIST_CTL_CMD_ENABLE:
 			case EVLIST_CTL_CMD_DISABLE:
 			case EVLIST_CTL_CMD_EVLIST:
+			case EVLIST_CTL_CMD_PING:
 			default:
 				break;
 			}

tools/perf/builtin-stat.c

@@ -623,6 +623,7 @@ static void process_evlist(struct evlist *evlist, unsigned int interval)
 		case EVLIST_CTL_CMD_UNSUPPORTED:
 		case EVLIST_CTL_CMD_EVLIST:
 		case EVLIST_CTL_CMD_STOP:
+		case EVLIST_CTL_CMD_PING:
 		default:
 			break;
 		}

tools/perf/util/evlist.c

@@ -1943,6 +1943,9 @@ static int evlist__ctlfd_recv(struct evlist *evlist, enum evlist_ctl_cmd *cmd,
 		} else if (!strncmp(cmd_data, EVLIST_CTL_CMD_STOP_TAG,
 				    (sizeof(EVLIST_CTL_CMD_STOP_TAG)-1))) {
 			*cmd = EVLIST_CTL_CMD_STOP;
+		} else if (!strncmp(cmd_data, EVLIST_CTL_CMD_PING_TAG,
+				    (sizeof(EVLIST_CTL_CMD_PING_TAG)-1))) {
+			*cmd = EVLIST_CTL_CMD_PING;
 		}
 	}
 
@@ -2081,6 +2084,7 @@ int evlist__ctlfd_process(struct evlist *evlist, enum evlist_ctl_cmd *cmd)
 				break;
 			case EVLIST_CTL_CMD_SNAPSHOT:
 			case EVLIST_CTL_CMD_STOP:
+			case EVLIST_CTL_CMD_PING:
 				break;
 			case EVLIST_CTL_CMD_ACK:
 			case EVLIST_CTL_CMD_UNSUPPORTED:

tools/perf/util/evlist.h

@@ -332,6 +332,7 @@ struct evsel *evlist__reset_weak_group(struct evlist *evlist, struct evsel *evse
 #define EVLIST_CTL_CMD_SNAPSHOT_TAG "snapshot"
 #define EVLIST_CTL_CMD_EVLIST_TAG "evlist"
 #define EVLIST_CTL_CMD_STOP_TAG "stop"
+#define EVLIST_CTL_CMD_PING_TAG "ping"
 
 #define EVLIST_CTL_CMD_MAX_LEN 64
 
@@ -343,6 +344,7 @@ enum evlist_ctl_cmd {
 	EVLIST_CTL_CMD_SNAPSHOT,
 	EVLIST_CTL_CMD_EVLIST,
 	EVLIST_CTL_CMD_STOP,
+	EVLIST_CTL_CMD_PING,
 };
 
 int evlist__parse_control(const char *str, int *ctl_fd, int *ctl_fd_ack, bool *ctl_fd_close);