trace-cmd: Have trace-cmd start wait for command unless --fork is specified

Commit Message

Steven Rostedt June 8, 2020, 8:39 p.m. UTC

[ I just realized I already pushed your patch. Here's an update to what
  I would like. ]

From: "Steven Rostedt (VMware)" <[e-mail]>

Instead of forking a command specified on the command line and returning
right away, have it wait for the process to finish before returning. Unless
"--fork" is specified as well.

Signed-off-by: Steven Rostedt (VMware) <[e-mail]>
---
 Documentation/trace-cmd-start.1.txt |  7 +++++++
 tracecmd/trace-record.c             | 18 +++++++++++++-----
 tracecmd/trace-usage.c              |  2 ++
 3 files changed, 22 insertions(+), 5 deletions(-)

Patch

diff --git a/Documentation/trace-cmd-start.1.txt b/Documentation/trace-cmd-start.1.txt
index 63d2034c..07f2ed3a 100644
--- a/Documentation/trace-cmd-start.1.txt
+++ b/Documentation/trace-cmd-start.1.txt
@@ -23,6 +23,13 @@  OPTIONS
 The options are the same as 'trace-cmd-record(1)', except that it does not
 take options specific to recording (*-s*, *-o*, *-N*, and *-t*).
 
+*--fork* ::
+   This option is only available for trace-cmd start. It tells trace-cmd
+   to not wait for the process to finish before returning.
+   With this option, trace-cmd start will return right after it forks
+   the process on the command line. This option only has an effect if
+   trace-cmd start also executes a command.
+
 SEE ALSO
 --------
 trace-cmd(1), trace-cmd-record(1), trace-cmd-report(1), trace-cmd-stop(1),
diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index 4d2039a1..143b736e 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -86,6 +86,8 @@  static char *host;
 
 static bool quiet;
 
+static bool fork_process;
+
 /* Max size to let a per cpu file get */
 static int max_kb;
 
@@ -1604,7 +1606,7 @@  static void run_cmd(enum trace_type type, const char *user, int argc, char **arg
 		/* child */
 		update_task_filter();
 		tracecmd_enable_tracing();
-		if (type != TRACE_TYPE_START)
+		if (!fork_process)
 			enable_ptrace();
 		/*
 		 * If we are using stderr for stdout, switch
@@ -1626,13 +1628,15 @@  static void run_cmd(enum trace_type type, const char *user, int argc, char **arg
 			die("Failed to exec %s", argv[0]);
 		}
 	}
-	if (type & TRACE_TYPE_START)
+	if (fork_process)
 		exit(0);
 	if (do_ptrace) {
 		ptrace_attach(NULL, pid);
 		ptrace_wait(type);
 	} else
 		trace_waitpid(type, pid, &status, 0);
+	if (type & TRACE_TYPE_START)
+		exit(0);
 }
 
 static void
@@ -5535,6 +5539,7 @@  void init_top_instance(void)
 }
 
 enum {
+	OPT_fork		= 241,
 	OPT_tsyncinterval	= 242,
 	OPT_user		= 243,
 	OPT_procmap		= 244,
@@ -5851,6 +5856,7 @@  static void parse_record_options(int argc,
 			{"user", required_argument, NULL, OPT_user},
 			{"module", required_argument, NULL, OPT_module},
 			{"tsync-interval", required_argument, NULL, OPT_tsyncinterval},
+			{"fork", no_argument, NULL, OPT_fork},
 			{NULL, 0, NULL, 0}
 		};
 
@@ -6204,6 +6210,11 @@  static void parse_record_options(int argc,
 			top_instance.tsync.loop_interval = atoi(optarg);
 			guest_sync_set = true;
 			break;
+		case OPT_fork:
+			if (!IS_START(ctx))
+				die("--fork option used for 'start' command only");
+			fork_process = true;
+			break;
 		case OPT_quiet:
 		case 'q':
 			quiet = true;
@@ -6266,9 +6277,6 @@  static void parse_record_options(int argc,
 		}
 	}
 
-	if (do_ptrace && IS_START(ctx))
-		die("ptrace not supported with command start");
-
 	for_all_instances(instance) {
 		if (instance->get_procmap && !instance->nr_filter_pids) {
 			warning("--proc-map is ignored for instance %s, "
diff --git a/tracecmd/trace-usage.c b/tracecmd/trace-usage.c
index 58bca9e4..1e832be8 100644
--- a/tracecmd/trace-usage.c
+++ b/tracecmd/trace-usage.c
@@ -71,6 +71,8 @@  static struct usage_help usage_help[] = {
 		" %s start [-e event][-p plugin][-d][-O option ][-P pid]\n"
 		"          Uses same options as record.\n"
 		"          It only enables the tracing and exits\n"
+		"\n"
+		"        --fork: If a command is specified, then return right after it forks\n"
 	},
 	{
 		"extract",