vmon: introduce -R/--reaper flag

Beginnings of PR_SET_CHILD_SUBREAPER mode, this only adds the
CLI flags.

Becoming a subreaper is only relevant to running commands via
vmon.  If the commands being executed fork/exec/daemonize or
otherwise may produce orphaned processes, they escape the
scoped hierarchical monitoring when init inherits them, so you
lose visibility into their actions once orphaned.

By becoming a subreaper, vmon can be the process inheriting those
orphans, so they may continue being monitored, as if vmon were
init, for its descendants.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/vmon.c b/src/vmon.c
index e49b360..059bcd5 100644
--- a/src/vmon.c
+++ b/src/vmon.c
@@ -49,6 +49,7 @@ typedef struct vmon_t {
 	int		linger;
 	int		dump_procs;
 	int		mem_locked;
+	int		reaper;
 	time_t		start_time;
 	int		snapshots_interval;
 	int		snapshot;
@@ -205,6 +206,7 @@ static void print_help(void)
 		" -v  --version     Print version\n"
 		" -D  --dump-procs  Dump libvmon internal processes table (debugging aid)\n"
 		" -L  --mem-locked  Lock in memory using mlockall(MCL_CURRENT|MCL_FUTURE)\n"
+		" -R  --reaper      Become the child subreaper (see prctl(2); PR_SET_CHILD_SUBREAPER)\n"
 		" -W  --width       Chart width\n"
 		" -z  --hertz       Sample rate in hertz\n"
 		"-------------------------------------------------------------------------------"
@@ -498,6 +500,9 @@ static int vmon_handle_argv(vmon_t *vmon, int argc, const char * const *argv)
 		} else if (is_flag(*argv, "-L", "--mem-locked")) {
 			vmon->mem_locked = 1;
 			last = argv;
+		} else if (is_flag(*argv, "-R", "--reaper")) {
+			vmon->reaper = 1;
+			last = argv;
 		} else if ((*argv)[0] == '-') {
 			VWM_ERROR("Unrecognized argument: \"%s\", try --help\n", argv[0]);
 			exit(EXIT_FAILURE);