perf daemon: Add config option

Add a config option and base functionality that takes the option
argument (if specified) and other system config locations and produces
an 'acting' config file path.

The actual config file processing is coming in following patches.
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/20210208200908.1019149-3-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-daemon.txt

@@ -27,6 +27,10 @@ OPTIONS
 --verbose::
 	Be more verbose.
 
+--config=<PATH>::
+	Config file path. If not provided, perf will check system and default
+	locations (/etc/perfconfig, $HOME/.perfconfig).
+
 All generic options are available also under commands.
 
 

tools/perf/builtin-daemon.c

@@ -3,14 +3,18 @@
 #include <linux/limits.h>
 #include <string.h>
 #include <signal.h>
+#include <stdlib.h>
 #include <stdio.h>
 #include <unistd.h>
 #include "builtin.h"
 #include "perf.h"
 #include "debug.h"
+#include "config.h"
 #include "util.h"
 
 struct daemon {
+	const char		*config;
+	char			*config_real;
 	char			*base;
 	FILE			*out;
 	char			 perf[PATH_MAX];
@@ -31,6 +35,32 @@ static void sig_handler(int sig __maybe_unused)
 	done = true;
 }
 
+static void daemon__exit(struct daemon *daemon)
+{
+	free(daemon->config_real);
+}
+
+static int setup_config(struct daemon *daemon)
+{
+	if (daemon->config) {
+		char *real = realpath(daemon->config, NULL);
+
+		if (!real) {
+			perror("failed: realpath");
+			return -1;
+		}
+		daemon->config_real = real;
+		return 0;
+	}
+
+	if (perf_config_system() && !access(perf_etc_perfconfig(), R_OK))
+		daemon->config_real = strdup(perf_etc_perfconfig());
+	else if (perf_config_global() && perf_home_perfconfig())
+		daemon->config_real = strdup(perf_home_perfconfig());
+
+	return daemon->config_real ? 0 : -1;
+}
+
 static int __cmd_start(struct daemon *daemon, struct option parent_options[],
 		       int argc, const char **argv)
 {
@@ -44,6 +74,11 @@ static int __cmd_start(struct daemon *daemon, struct option parent_options[],
 	if (argc)
 		usage_with_options(daemon_usage, start_options);
 
+	if (setup_config(daemon)) {
+		pr_err("failed: config not found\n");
+		return -1;
+	}
+
 	debug_set_file(daemon->out);
 	debug_set_display_time(true);
 
@@ -56,6 +91,8 @@ static int __cmd_start(struct daemon *daemon, struct option parent_options[],
 		sleep(1);
 	}
 
+	daemon__exit(daemon);
+
 	pr_info("daemon exited\n");
 	fclose(daemon->out);
 	return err;
@@ -65,6 +102,8 @@ int cmd_daemon(int argc, const char **argv)
 {
 	struct option daemon_options[] = {
 		OPT_INCR('v', "verbose", &verbose, "be more verbose"),
+		OPT_STRING(0, "config", &__daemon.config,
+			"config file", "config file path"),
 		OPT_END()
 	};
 
@@ -82,5 +121,10 @@ int cmd_daemon(int argc, const char **argv)
 		return -1;
 	}
 
+	if (setup_config(&__daemon)) {
+		pr_err("failed: config not found\n");
+		return -1;
+	}
+
 	return -1;
 }