usttrace: add comments to describe start sequence of ustd

diff --git a/usttrace b/usttrace
index 1db591f366495b14df7007a2a7ac026d6f541a70..15336f638d91ab7133842d149456667b3033d162 100755 (executable)
--- a/usttrace
+++ b/usttrace
@@ -87,6 +87,13 @@ then
        mkfifo -m 0600 "$pidfilepath"
        # Start daemon
        $USTD --pidfile "$pidfilepath" -s "$SOCKPATH" -o "$OUTDIR" >"$OUTDIR/ustd.log" 2>&1 &
+       # ustd sets up its server socket
+       # ustd opens the pidfile, blocks because no one has opened it
+       # we open pidfile
+       # we block reading pidfile
+       # ustd writes to pidfile
+       # ustd closes pidfile
+       # we unblock reading pidfile
        USTDPID="$(<$pidfilepath)"
        export UST_DAEMON_SOCKET="$SOCKPATH"
 fi