perf_counter tools: add 'perf help'

perf-help(1)

===========

NAME

----

perf-help - display help information about perf

SYNOPSIS

--------

'perf help' [-a|--all] [COMMAND]

DESCRIPTION

-----------

With no options and no COMMAND given, the synopsis of the 'perf'

command and a list of the most commonly used perf commands are printed

on the standard output.

If the option '--all' or '-a' is given, then all available commands are

printed on the standard output.

If a perf command is named, a manual page for that command is brought

up. The 'man' program is used by default for this purpose, but this

can be overridden by other options or configuration variables.

Note that `perf --help ...` is identical to `perf help ...` because the

former is internally converted into the latter.

OPTIONS

-------

-a::

--all::

	Prints all the available commands on the standard output. This

	option supersedes any other option.

PERF

----

Part of the linkperf:perf[1] suite

extern int read_line_with_nul(char *buf, int size, FILE *file);

extern int check_pager_config(const char *cmd);

extern int cmd_help(int argc, const char **argv, const char *prefix);

extern int cmd_record(int argc, const char **argv, const char *prefix);

extern int cmd_stat(int argc, const char **argv, const char *prefix);

extern int cmd_top(int argc, const char **argv, const char *prefix);

{

	const char *cmd = argv[0];

	static struct cmd_struct commands[] = {

		{ "help", cmd_help, 0 },

		{ "record", cmd_record, 0 },

		{ "stat", cmd_stat, 0 },

		{ "top", cmd_top, 0 },