[PATCH v3] nfs-blkmapd: PID file read by systemd failed

[zhanchengbin <zhanchengbin1@huawei.com>]

When started nfs-blkmap.service, the PID file can't be opened, The
cause is that the child process does not create the PID file before
the systemd reads the PID file.
Adding "ExecStartPost=/bin/sleep 0.1" to
/usr/lib/systemd/system/nfs-blkmap.service will probably solve this
problem, However, there is no guarantee that the above solutions are
effective under high cpu pressure.So replace the daemon function with
the fork function, and put the behavior of creating the PID file in
the parent process to solve the above problems.

Signed-off-by: zhanchengbin <zhanchengbin1@huawei.com>
Reviewed-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
---
V2->V3:
  Replace "fprintf(stderr" with BL_LOG_ERR.

  utils/blkmapd/device-discovery.c | 48 +++++++++++++++++++++-----------
  1 file changed, 32 insertions(+), 16 deletions(-)

diff --git a/utils/blkmapd/device-discovery.c 
b/utils/blkmapd/device-discovery.c
index bd890598..a565fdbd 100644
--- a/utils/blkmapd/device-discovery.c
+++ b/utils/blkmapd/device-discovery.c
@@ -498,28 +498,44 @@ int main(int argc, char **argv)
  	if (fg) {
  		openlog("blkmapd", LOG_PERROR, 0);
  	} else {
-		if (daemon(0, 0) != 0) {
-			fprintf(stderr, "Daemonize failed\n");
+		pid_t pid = fork();
+		if (pid < 0) {
+			BL_LOG_ERR("fork error\n");
  			exit(1);
+		} else if (pid != 0) {
+			pidfd = open(PID_FILE, O_WRONLY | O_CREAT, 0644);
+			if (pidfd < 0) {
+				BL_LOG_ERR("Create pid file %s failed\n", PID_FILE);
+				exit(1);
+			}
+
+			if (lockf(pidfd, F_TLOCK, 0) < 0) {
+				BL_LOG_ERR("Already running; Exiting!");
+				close(pidfd);
+				exit(1);
+			}
+			if (ftruncate(pidfd, 0) < 0)
+				BL_LOG_ERR("ftruncate on %s failed: m\n", PID_FILE);
+			sprintf(pidbuf, "%d\n", pid);
+			if (write(pidfd, pidbuf, strlen(pidbuf)) != (ssize_t)strlen(pidbuf))
+				BL_LOG_ERR("write on %s failed: m\n", PID_FILE);
+			exit(0);
  		}

-		openlog("blkmapd", LOG_PID, 0);
-		pidfd = open(PID_FILE, O_WRONLY | O_CREAT, 0644);
-		if (pidfd < 0) {
-			BL_LOG_ERR("Create pid file %s failed\n", PID_FILE);
-			exit(1);
+		(void)setsid();
+		if (chdir("/")) {
+			BL_LOG_ERR("chdir error\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);

-		if (lockf(pidfd, F_TLOCK, 0) < 0) {
-			BL_LOG_ERR("Already running; Exiting!");
-			close(pidfd);
-			exit(1);
+		    (void)close(fd);
  		}
-		if (ftruncate(pidfd, 0) < 0)
-			BL_LOG_WARNING("ftruncate on %s failed: m\n", PID_FILE);
-		sprintf(pidbuf, "%d\n", getpid());
-		if (write(pidfd, pidbuf, strlen(pidbuf)) != (ssize_t)strlen(pidbuf))
-			BL_LOG_WARNING("write on %s failed: m\n", PID_FILE);
+
+		openlog("blkmapd", LOG_PID, 0);
  	}

  	signal(SIGINT, sig_die);
-- 
2.27.0