ftrace/selftests: Add softlink to latest log directory

When I'm debugging something with the ftrace selftests and need to look at
the logs, it becomes tedious that I need to do the following:

ls -ltr logs
[ copy the last directory ]
ls logs/<paste-last-dir>

to see where the logs are.

Instead, do the common practice of having a "latest" softlink to the last
run selftest. This way after running the selftest I only need to do:

ls logs/latest/

and it will always give me the directory of the last run selftest logs!

Signed-off-by: Steven Rostedt (Google) <[e-mail]>
Acked-by: Masami Hiramatsu (Google) <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/ftrace/ftracetest

···
     ;;
     --logdir|-l)
       LOG_DIR=$2
+      LINK_PTR=
       shift 2
     ;;
     *.tc)
···
 TOP_DIR=`absdir $0`
 TEST_DIR=$TOP_DIR/test.d
 TEST_CASES=`find_testcases $TEST_DIR`
-LOG_DIR=$TOP_DIR/logs/`date +%Y%m%d-%H%M%S`/
+LOG_TOP_DIR=$TOP_DIR/logs
+LOG_DATE=`date +%Y%m%d-%H%M%S`
+LOG_DIR=$LOG_TOP_DIR/$LOG_DATE/
+LINK_PTR=$LOG_TOP_DIR/latest
 KEEP_LOG=0
 KTAP=0
 DEBUG=0
···
   LOG_FILE=$LOG_DIR/ftracetest.log
   mkdir -p $LOG_DIR || errexit "Failed to make a log directory: $LOG_DIR"
   date > $LOG_FILE
+  if [ "x-$LINK_PTR" != "x-" ]; then
+    unlink $LINK_PTR
+    ln -fs $LOG_DATE $LINK_PTR
+  fi
 fi
 
 # Define text colors