linux-ext4 - [PATCH] quota-nld: fix open PID file failed when systemd read it

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Date:   Thu, 1 Dec 2022 12:10:49 +0800
From:   "lihaoxiang (F)" <lihaoxiang9@...wei.com>
To:     <jack@...e.cz>
CC:     <linux-ext4@...r.kernel.org>,
        Zhiqiang Liu <liuzhiqiang26@...wei.com>,
        <linfeilong@...wei.com>, <louhongxiang@...wei.com>,
        "lijinlin (A)" <lijinlin3@...wei.com>
Subject: [PATCH] quota-nld: fix open PID file failed when systemd read it

Running quota_nld by systemd might cause the problem that systemd
couldn't open the PID file generated by quota_nld. In fact, the PID
file hasn't existed yet because it originates from the child process
of quota_nld which is a daemon process. As the main process exit,
systemd try to access the PID file but the daemon hadn't create it
that time.

In this situation, we move the procedure of creating PID file into the
parent process to ensure the PID file must existed when quota_nld exit.
After that, the above problem would never occur again.

Signed-off-by: lihaoxiang <lihaoxiang9@...wei.com>
---
 quota_nld.c | 43 +++++++++++++++++++++++++++++++++----------
 1 file changed, 33 insertions(+), 10 deletions(-)

diff --git a/quota_nld.c b/quota_nld.c
index 09c4775..4a02eb1 100644
--- a/quota_nld.c
+++ b/quota_nld.c
@@ -413,7 +413,7 @@ static char *build_pid_file_name(void)
 }

 /* Store daemon's PID to file */
-static int store_pid(void)
+static int store_pid(pid_t pid)
 {
 	FILE *pid_file;
 	char *pid_name;
@@ -429,7 +429,7 @@ static int store_pid(void)
 		free(pid_name);
 		return -1;
 	}
-	if (fprintf(pid_file, "%jd\n", (intmax_t)getpid()) < 0) {
+	if (fprintf(pid_file, "%jd\n", pid) < 0) {
 		errstr(_("Could not write daemon's PID into '%s'.\n"),
 			pid_name);
 		fclose(pid_file);
@@ -460,7 +460,7 @@ static void remove_pid(int signal)
 }

 /* Store daemon's PID into file and register its removal on SIGTERM */
-static void use_pid_file(void)
+static void use_pid_file(pid_t pid)
 {
 	struct sigaction term_action;

@@ -468,8 +468,35 @@ static void use_pid_file(void)
 	term_action.sa_flags = 0;
 	if (sigemptyset(&term_action.sa_mask) || sigaction(SIGTERM, &term_action, NULL))
 		errstr(_("Could not register PID file removal on SIGTERM.\n"));
-	if (store_pid())
-		errstr(_("Could not store my PID %jd.\n"), (intmax_t )getpid());
+	if (store_pid(pid))
+		errstr(_("Could not store my PID %jd.\n"), pid);
+}
+
+static void fork_daemon()
+{
+	pid_t pid = fork();
+	if (pid < 0) {
+		errstr(_("Failed to daemonize: fork error with %s\n"), strerror(errno));
+		exit(1);
+	} else if (pid != 0) {
+		use_pid_file(pid);
+		exit(0);
+	}
+
+	if (setsid() == -1) {
+		errstr(_("Failed to daemonize: setsid error with %s\n"), strerror(errno));
+		exit(1);
+	}
+	if (chdir("/"))
+		errstr(_("Failed to chdir in daemonize \n"));
+	int fd = open("/dev/null", O_RDWR, 0);
+	if (fd >= 0) {
+		(void)dup2(fd, STDIN_FILENO);
+		(void)dup2(fd, STDOUT_FILENO);
+		(void)dup2(fd, STDERR_FILENO);
+
+		(void)close(fd);
+	}
 }

 int main(int argc, char **argv)
@@ -485,11 +512,7 @@ int main(int argc, char **argv)
 		dhandle = init_dbus();
 	if (!(flags & FL_NODAEMON)) {
 		use_syslog();
-		if (daemon(0, 0)) {
-			errstr(_("Failed to daemonize: %s\n"), strerror(errno));
-			exit(1);
-		};
-		use_pid_file();
+		fork_daemon();
 	}
 	run(nsock);
 	return 0;
-- 
2.37.0.windows.1