PR6930: stapio: run in background as a daemon

Add '-D'(daemon mode) option to staprun/stapio for daemon mode.
In this mode, stapio shows just its pid and detachs from console.
Since it has no stdio, this mode requires -o option. stapio will
exit when it receives SIGTERM or detects some error.

3 files changed, 84 insertions, 4 deletions

diff --git a/runtime/staprun/common.c b/runtime/staprun/common.c
index b8860248..a1b70d3b 100644
--- a/runtime/staprun/common.c
+++ b/runtime/staprun/common.c
@@ -27,6 +27,7 @@ int attach_mod;
 int delete_mod;
 int load_only;
 int need_uprobes;
+int daemon_mode;
 
 /* module variables */
 char *modname = NULL;
@@ -35,6 +36,21 @@ char *modoptions[MAXMODOPTIONS];
 
 int control_channel = -1; /* NB: fd==0 possible */
 
+static char path_buf[PATH_MAX];
+static char *get_abspath(char *path)
+{
+	int len;
+	if (path[0] == '/')
+		return path;
+
+	len = strlen(getcwd(path_buf, PATH_MAX));
+	if (len + 2 + strlen(path) >= PATH_MAX)
+		return NULL;
+	path_buf[len] = '/';
+	strcpy(&path_buf[len + 1], path);
+	return path_buf;
+}
+
 void parse_args(int argc, char **argv)
 {
 	int c;
@@ -49,8 +65,9 @@ void parse_args(int argc, char **argv)
 	delete_mod = 0;
 	load_only = 0;
 	need_uprobes = 0;
+	daemon_mode = 0;
 
-	while ((c = getopt(argc, argv, "ALuvb:t:dc:o:x:")) != EOF) {
+	while ((c = getopt(argc, argv, "ALuvb:t:dc:o:x:D")) != EOF) {
 		switch (c) {
 		case 'u':
 			need_uprobes = 1;
@@ -85,11 +102,20 @@ void parse_args(int argc, char **argv)
 		case 'L':
 			load_only = 1;
 			break;
+		case 'D':
+			daemon_mode = 1;
+			break;
 		default:
 			usage(argv[0]);
 		}
 	}
-
+	if (outfile_name) {
+		outfile_name = get_abspath(outfile_name);
+		if (outfile_name == NULL) {
+			err("File name is too long.\n");
+			usage(argv[0]);
+		}
+	}
 	if (attach_mod && load_only) {
 		err("You can't specify the '-A' and '-L' options together.\n");
 		usage(argv[0]);
@@ -118,12 +144,29 @@ void parse_args(int argc, char **argv)
 		err("You can't specify the '-c' and '-x' options together.\n");
 		usage(argv[0]);
 	}
+
+	if (daemon_mode && load_only) {
+		err("You can't specify the '-D' and '-L' options together.\n");
+		usage(argv[0]);
+	}
+	if (daemon_mode && delete_mod) {
+		err("You can't specify the '-D' and '-d' options together.\n");
+		usage(argv[0]);
+	}
+	if (daemon_mode && target_cmd) {
+		err("You can't specify the '-D' and '-c' options together.\n");
+		usage(argv[0]);
+	}
+	if (daemon_mode && outfile_name == NULL) {
+		err("You have to specify output FILE with '-D' option.\n");
+		usage(argv[0]);
+	}
 }
 
 void usage(char *prog)
 {
-	err("\n%s [-v]  [-c cmd ] [-x pid] [-u user]\n"
-                "\t[-A|-L] [-b bufsize] [-o FILE] MODULE [module-options]\n", prog);
+	err("\n%s [-v]  [-c cmd ] [-x pid] [-u user] [-A|-L|-d]\n"
+                "\t[-b bufsize] [-o FILE [-D]] MODULE [module-options]\n", prog);
 	err("-v              Increase verbosity.\n");
 	err("-c cmd          Command \'cmd\' will be run and staprun will\n");
 	err("                exit when it does.  The '_stp_target' variable\n");
@@ -140,6 +183,7 @@ void usage(char *prog)
 	err("-d              Delete a module.  Only detached or unused modules\n");
 	err("                the user has permission to access will be deleted. Use \"*\"\n");
 	err("                (quoted) to delete all unused modules.\n");
+	err("-D              Run in background. This requires '-o' option.\n");
 	err("MODULE can be either a module name or a module path.  If a\n");
 	err("module name is used, it is looked for in the following\n");
 	err("directory: /lib/modules/`uname -r`/systemtap\n");
diff --git a/runtime/staprun/mainloop.c b/runtime/staprun/mainloop.c
index e91e6302..b0d88073 100644
--- a/runtime/staprun/mainloop.c
+++ b/runtime/staprun/mainloop.c
@@ -318,6 +318,41 @@ int init_stapio(void)
   if (target_cmd)
     start_cmd();
 
+  /* Run in background */
+  if (daemon_mode) {
+    pid_t pid;
+    int ret;
+    dbug(2, "daemonizing stapio\n");
+
+    /* daemonize */
+    ret = daemon(0, 1); /* don't close stdout at this time. */
+    if (ret) {
+      err("Failed to daemonize stapio\n");
+      return -1;
+    }
+
+    /* change error messages to syslog. */
+    switch_syslog("stapio");
+
+    /* show new pid */
+    pid = getpid();
+    fprintf(stdout, "%d\n", pid);
+    fflush(stdout);
+
+    /* redirect all outputs to /dev/null */
+    ret = open("/dev/null", O_RDWR);
+    if (ret < 0) {
+      err("Failed to open /dev/null\n");
+      return -1;
+    }
+    close(STDIN_FILENO);
+    close(STDOUT_FILENO);
+    close(STDERR_FILENO);
+    dup2(ret, STDOUT_FILENO);
+    dup2(ret, STDERR_FILENO);
+    close(ret);
+  }
+
   return 0;
 }
 
diff --git a/runtime/staprun/staprun.h b/runtime/staprun/staprun.h
index 4c43e3ee..b380cebd 100644
--- a/runtime/staprun/staprun.h
+++ b/runtime/staprun/staprun.h
@@ -157,6 +157,7 @@ extern int attach_mod;
 extern int delete_mod;
 extern int load_only;
 extern int need_uprobes;
+extern int daemon_mode;
 
 /* getopt variables */
 extern char *optarg;