vmon: trigger final snapshot on SIGTERM

When using vmon to monitor a system PID1 will kill it @
shutdown/reboot, and we should save one last snapshot of what's
been captured before we exit in that case.

SIGTERM is sent first before the SIGKILL killing spree, so let's
handle the SIGTERM by writing the snapshot, then exiting the main
loop.

The service manager can then do something with the produced
snapshots after we've exited, if they're considered interesting.

1 files changed, 26 insertions, 4 deletions

diff --git a/src/vmon.c b/src/vmon.c
index 576aebc..0631084 100644
--- a/src/vmon.c
+++ b/src/vmon.c
@@ -66,7 +66,7 @@ typedef struct vmon_t {
 #define WIDTH_MIN	200
 #define HEIGHT_MIN	28
 
-static volatile int got_sigchld, got_sigusr1, got_sigint, got_sigquit;
+static volatile int got_sigchld, got_sigusr1, got_sigint, got_sigquit, got_sigterm;
 
 /* return if arg == flag or altflag if provided */
 static int is_flag(const char *arg, const char *flag, const char *altflag)
@@ -193,8 +193,8 @@ static void print_help(void)
 		" -N  --now-names   Use current time in filenames instead of start time\n"
 		" -o  --output-dir  Directory to store saved output to (\".\" if unspecified)\n"
 		" -p  --pid         PID of the top-level process to monitor (1 if unspecified)\n"
-		" -i  --snapshots   Save a PNG snapshot every N seconds (SIGUSR1 also snapshots)\n"
-		" -s  --snapshot    Save a PNG snapshot upon receiving SIGCHLD\n"
+		" -i  --snapshots   Save a PNG snapshot every N seconds (SIG{TERM,USR1} also snapshots)\n"
+		" -s  --snapshot    Save a PNG snapshot upon receiving SIG{CHLD,TERM,USR1}\n"
 		" -w  --wip-name    Name to use for work-in-progress snapshot filename\n"
 		" -v  --version     Print version\n"
 		" -W  --width       Chart width\n"
@@ -223,25 +223,35 @@ static void print_copyright(void)
 }
 
 
-/* collect status of child */
+/* collect status of child, triggering snapshot if snapshotting active */
 static void handle_sigchld(int signum)
 {
 	got_sigchld = 1;
 }
 
 
+/* trigger a snapshot */
 static void handle_sigusr1(int signum)
 {
 	got_sigusr1 = 1;
 }
 
 
+/* trigger a snapshot and exit immediately after it's been written */
+static void handle_sigterm(int signum)
+{
+	got_sigterm = 1;
+}
+
+
+/* propagates to child first time, quits second time */
 static void handle_sigint(int signum)
 {
 	got_sigint++;
 }
 
 
+/* propagates to child first time, quits second time */
 static void handle_sigquit(int signum)
 {
 	got_sigquit++;
@@ -622,6 +632,11 @@ static vmon_t * vmon_startup(int argc, const char * const *argv)
 		goto _err_vcr;
 	}
 
+	if (signal(SIGTERM, handle_sigterm) == SIG_ERR) {
+		VWM_PERROR("unable to set SIGTERM handler");
+		goto _err_vcr;
+	}
+
 	if (vmon->snapshots_interval) {
 		int	r;
 
@@ -855,6 +870,13 @@ int main(int argc, const char * const *argv)
 			got_sigquit++;
 
 			kill(vmon->pid, SIGQUIT);
+		} else if (got_sigterm) {
+			if (vmon->snapshot || vmon->snapshots_interval) {
+				/* simulate sigusr1 to trigger a final snapshot, */
+				got_sigusr1 = 1;
+			}
+
+			vmon->done = 1;
 		}
 
 		if (got_sigchld) {