vmon: add %P fmt specifier for getpid()

vmon already handles SIGUSR1 for producing png snapshots on
demand, adding a fmt specifier for substituting the vmon PID
makes for convenient scripting of triggering such snapshots.

i.e:

$ vmon -- /bin/bash -c 'for((i = 0; i < 10; i++)); do kill -USR1 %P; sleep 1s; done'

Would produce ten png snapshots of the charts on 1-second
intervals.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/vmon.c b/src/vmon.c
index 7d0a5f7..59f89ad 100644
--- a/src/vmon.c
+++ b/src/vmon.c
@@ -345,6 +345,11 @@ static char * arg_interpolate(const vmon_t *vmon, const char *arg)
 			fprintf(memfp, "%s", vmon->output_dir);
 			break;
 
+		case 'P':	/* getpid() of vmon, convenient for triggering png snapshots on SIGUSR1 */
+				/* XXX: note this assumes arg_interpolate() occurs pre-fork, true ATM  */
+			fprintf(memfp, "%li", (long)getpid());
+			break;
+
 		case '%':	/* literal % */
 			fputc(c, memfp);
 			break;