From: Kienan Stewart <kstewart@efficios.com>
Date: Tue, 12 Nov 2024 20:23:06 +0000 (-0500)
Subject: lttng-relayd: Add `--pid-file` parameter
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=58b8d49ba10e6f2438ec6ef6662c510e9a94451b;p=lttng-tools.git

lttng-relayd: Add `--pid-file` parameter

Intended to be used a mechanism to get the PID of the process when
starting with `-b` or `-d`.

`lttng-sessiond` writes to a well-known path inside `$LTTNG_HOME`
instead.

The exit for the lttng-relayd `main()` function is changed from
`exit()` to `return`. When using `exit()` or `std::exit()`, the
end-of-scope objects (e.g. from `lttng::make_scope_exit()` do not
fire.

Change-Id: I1ce6fd316356ac251cb3a0c0039c565f1ca1210f
Signed-off-by: Kienan Stewart <kstewart@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---

diff --git a/doc/man/lttng-relayd.8.txt b/doc/man/lttng-relayd.8.txt
index 3d1a0071f..3f38b2fe0 100644
--- a/doc/man/lttng-relayd.8.txt
+++ b/doc/man/lttng-relayd.8.txt
@@ -18,7 +18,7 @@ SYNOPSIS
              [option:--live-port='URL'] [option:--output='DIR'] [option:--group='GROUP']
              [option:--verbose]... [option:--working-directory='DIR']
              [option:--group-output-by-host | option:--group-output-by-session] [option:--disallow-clear]
-	     [option:--dynamic-port-allocation]
+	     [option:--dynamic-port-allocation] [option:--pid-file='FILE']
 
 
 DESCRIPTION
@@ -236,6 +236,11 @@ option:--dynamic-port-allocation::
 lttng-relayd will write `control.port`, `data.port`, and `live.port` files to
 its run-time directory.
 
+option:-P, option:--pid-file::
+    Write the PID of the lttng-relayd process to the given file.
++
+This file is not otherwise used by lttng-relayd and is removed at shutdown.
+
 Output
 ~~~~~~
 See the ``<<output-directory,Output directory>>'' section above to learn
diff --git a/src/bin/lttng-relayd/main.cpp b/src/bin/lttng-relayd/main.cpp
index f8fcee2a1..c5485dfa1 100644
--- a/src/bin/lttng-relayd/main.cpp
+++ b/src/bin/lttng-relayd/main.cpp
@@ -44,6 +44,7 @@
 #include <common/ini-config/ini-config.hpp>
 #include <common/path.hpp>
 #include <common/pthread-lock.hpp>
+#include <common/scope-exit.hpp>
 #include <common/sessiond-comm/inet.hpp>
 #include <common/sessiond-comm/relayd.hpp>
 #include <common/sessiond-comm/sessiond-comm.hpp>
@@ -96,8 +97,9 @@ enum relay_connection_status {
 };
 
 /* command line options */
-char *opt_output_path, *opt_working_directory;
-static int opt_daemon, opt_background, opt_print_version, opt_allow_clear = 1, opt_dynamic_port_allocation = 0;
+char *opt_output_path, *opt_working_directory, *opt_pid_file = nullptr;
+static int opt_daemon, opt_background, opt_print_version,
+	opt_allow_clear = 1, opt_dynamic_port_allocation = 0;
 enum relay_group_output_by opt_group_output_by = RELAYD_GROUP_OUTPUT_BY_UNKNOWN;
 
 /* Argument variables */
@@ -212,6 +214,12 @@ static struct option long_options[] = {
 		nullptr,
 		'b',
 	},
+	{
+		"pid-file",
+		1,
+		nullptr,
+		'P'
+	},
 	{
 		"group",
 		1,
@@ -381,6 +389,15 @@ static int set_option(int opt, const char *arg, const char *optname)
 	case 'b':
 		opt_background = 1;
 		break;
+	case 'P':
+		opt_pid_file = utils_partial_realpath(arg);
+		if (opt_pid_file == nullptr) {
+			ret = -1;
+			ERR_FMT("Failed to determine partial realpath for PID file at path '{}'",
+				arg);
+			goto end;
+		}
+		break;
 	case 'g':
 		if (lttng_is_setuid_setgid()) {
 			WARN("Getting '%s' argument from setuid/setgid binary refused for security reasons.",
@@ -4353,6 +4370,14 @@ int main(int argc, char **argv)
 	int ret = 0, retval = 0;
 	void *status;
 	char *unlinked_file_directory_path = nullptr, *output_path = nullptr;
+	auto delete_pid_file = lttng::make_scope_exit([]() noexcept {
+		if (opt_pid_file != nullptr) {
+			if (unlink(opt_pid_file)) {
+				PERROR_FMT("Failed to delete PID file at path '{}'", opt_pid_file);
+			}
+		}
+	});
+	delete_pid_file.disarm();
 
 	/* Parse environment variables */
 	ret = parse_env_options();
@@ -4425,6 +4450,15 @@ int main(int argc, char **argv)
 		}
 	}
 
+	if (opt_pid_file != nullptr) {
+		ret = utils_create_pid_file(getpid(), opt_pid_file);
+		if (ret) {
+			ERR_FMT("Failed to create PID file at path '{}'", opt_pid_file);
+			goto exit_options;
+		}
+		delete_pid_file.arm();
+	}
+
 	sessiond_trace_chunk_registry = sessiond_trace_chunk_registry_create();
 	if (!sessiond_trace_chunk_registry) {
 		ERR("Failed to initialize session daemon trace chunk registry");
@@ -4639,8 +4673,8 @@ exit_options:
 	}
 
 	if (!retval) {
-		exit(EXIT_SUCCESS);
+		return EXIT_SUCCESS;
 	} else {
-		exit(EXIT_FAILURE);
+		return EXIT_FAILURE;
 	}
 }