common: compile libcommon as C++

[lttng-tools.git] / src / common / daemonize.cpp

diff --git a/src/common/daemonize.cpp b/src/common/daemonize.cpp
new file mode 100644 (file)
index 0000000..16af5a3
--- /dev/null
+++ b/src/common/daemonize.cpp
@@ -0,0 +1,121 @@
+/*
+ * Copyright (C) 2013 David Goulet <dgoulet@efficios.com>
+ * Copyright (C) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-only
+ *
+ */
+
+#define _LGPL_SOURCE
+#include <unistd.h>
+#include <common/compat/paths.h>
+#include <fcntl.h>
+#include <sys/wait.h>
+#include <stdlib.h>
+
+#include <urcu/system.h>
+
+#include <common/daemonize.h>
+#include <common/error.h>
+
+int lttng_daemonize(pid_t *child_ppid, int *completion_flag,
+               int close_fds)
+{
+       pid_t pid;
+
+       /* Get parent pid of this process. */
+       *child_ppid = getppid();
+
+       pid = fork();
+       if (pid < 0) {
+               PERROR("fork");
+               goto error;
+       } else if (pid == 0) {
+               int fd;
+               pid_t sid;
+               int ret;
+
+               /* Child */
+
+               /*
+                * Get the newly created parent pid so we can signal
+                * that process when we are ready to operate.
+                */
+               *child_ppid = getppid();
+
+               sid = setsid();
+               if (sid < 0) {
+                       PERROR("setsid");
+                       goto error;
+               }
+
+               /*
+                * Try to change directory to /. If we can't well at
+                * least notify.
+                */
+               ret = chdir("/");
+               if (ret < 0) {
+                       PERROR("chdir");
+               }
+
+               if (close_fds) {
+                       fd = open(_PATH_DEVNULL, O_RDWR, 0);
+                       if (fd < 0) {
+                               PERROR("open %s", _PATH_DEVNULL);
+                               /*
+                                * Let 0, 1 and 2 open since we can't
+                                * bind them to /dev/null.
+                                */
+                       } else {
+                               (void) dup2(fd, STDIN_FILENO);
+                               (void) dup2(fd, STDOUT_FILENO);
+                               (void) dup2(fd, STDERR_FILENO);
+                               if (fd > 2) {
+                                       ret = close(fd);
+                                       if (ret < 0) {
+                                               PERROR("close");
+                                       }
+                               }
+                       }
+               }
+               goto end;
+       } else {
+               /* Parent */
+
+               /*
+                * Waiting for child to notify this parent that it can
+                * exit. Note that sleep() is interrupted before the 1
+                * second delay as soon as the signal is received, so it
+                * will not cause visible delay for the user.
+                */
+               while (!CMM_LOAD_SHARED(*completion_flag)) {
+                       int status;
+                       pid_t ret;
+
+                       /*
+                        * Check if child exists without blocking. If
+                        * so, we have to stop this parent process and
+                        * return an error.
+                        */
+                       ret = waitpid(pid, &status, WNOHANG);
+                       if (ret < 0 || (ret != 0 && WIFEXITED(status))) {
+                               /* The child exited somehow or was not valid. */
+                               goto error;
+                       }
+                       sleep(1);
+               }
+
+               /*
+                * From this point on, the parent can exit and the child
+                * is now an operational session daemon ready to serve
+                * clients and applications.
+                */
+               exit(EXIT_SUCCESS);
+       }
+
+end:
+       return 0;
+
+error:
+       return -1;
+}