perf daemon: Add 'ping' command

Add a 'ping' command to verify that the 'perf record' session is up and
operational.

It's used in the following patches via test code to make sure 'perf
record' is ready to receive signals.

Example:

  # cat ~/.perfconfig
  [daemon]
  base=/opt/perfdata

  [session-cycles]
  run = -m 10M -e cycles --overwrite --switch-output -a

  [session-sched]
  run = -m 20M -e sched:* --overwrite --switch-output -a

Start the daemon:

  # perf daemon start

Ping all sessions:

  # perf daemon ping
  OK   cycles
  OK   sched

Ping specific session:

  # perf daemon ping --session sched
  OK   sched

Committer notes:

Fixed up bug pointed by clang:

Buggy:

  if (!pollfd.revents & POLLIN)

Correct code:

  if (!(pollfd.revents & POLLIN))

clang warning:

  builtin-daemon.c:560:6: error: logical not is only applied to the left hand side of this bitwise operator [-Werror,-Wlogical-not-parentheses]
          if (!pollfd.revents & POLLIN) {
              ^               ~
  builtin-daemon.c:560:6: note: add parentheses after the '!' to evaluate the bitwise operator first

Also use designated initialized with pollfd, i.e.:

  struct pollfd pollfd = { .events = POLLIN, };

Instead of:

  struct pollfd pollfd = { 0, };

To get past:

    builtin-daemon.c:510:30: error: missing field 'events' initializer [-Werror,-Wmissing-field-initializers]
            struct pollfd pollfd = { 0, };
                                        ^
    1 error generated.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexei Budankov <abudankov@huawei.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: https://lore.kernel.org/r/20210208200908.1019149-16-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/tools/perf/Documentation/perf-daemon.txt b/tools/perf/Documentation/perf-daemon.txt
index b1acd468b89c..90b20bea6356 100644
--- a/tools/perf/Documentation/perf-daemon.txt
+++ b/tools/perf/Documentation/perf-daemon.txt
@@ -15,6 +15,7 @@ SYNOPSIS
 'perf daemon start'  [<options>]
 'perf daemon stop'   [<options>]
 'perf daemon signal' [<options>]
+'perf daemon ping'   [<options>]
 
 
 DESCRIPTION
@@ -80,6 +81,14 @@ The signal command sends signal to configured sessions.
 	Send signal to specific session.
 
 
+PING COMMAND
+------------
+The ping command sends control ping to configured sessions.
+
+--session::
+	Send ping to specific session.
+
+
 CONFIG FILE
 -----------
 The daemon is configured within standard perf config file by