selftests/ftrace: Add check for ping command for trigger tests

All these tests depend on the ping command and will fail if it is not
found. Allow tests to specify dependencies on programs through the
'requires' field. Add dependency on 'ping' for some of the trigger
tests.

Link: https://lore.kernel.org/all/20221017104312.16af5467@gandalf.local.home/
Reported-by: Akanksha J N <akanksha@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Suggested-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

selftests/ftrace: Support ":README" suffix for requires

Add ":README" suffix support for the requires list, so that
the testcase can list up the required string for README file
to the requires list.

Note that the required string is treated as a fixed string,
instead of regular expression. Also, the testcase can specify
a string containing spaces with quotes. E.g.

# requires: "place: [<module>:]<symbol>":README

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

selftests/ftrace: Convert required interface checks into requires list

Convert the required tracefs interface checking code with
requires: list.

Fixed merge conflicts in trigger-hist.tc and trigger-trace-marker-hist.tc
Shuah Khan <skhan@linuxfoundation.org>

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

selftests/ftrace: Do not to use absolute debugfs path

Use relative path to trigger file instead of absolute debugfs path,
because if the user uses tracefs instead of debugfs, it can be
mounted at /sys/kernel/tracing.
Anyway, since the ftracetest is designed to be run at the tracing
directory, user doesn't need to use absolute path.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tracing: Add hist trigger onchange() handler test case

Add a test case verifying the basic functionality of the
hist:onchange($var) handler.

Link: http://lkml.kernel.org/r/bec87aa8ed7d81794510b3d465096a750c71fce7.1550100284.git.tom.zanussi@linux.intel.com

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>