[PATCH rcu 4/8] tools: rcu: Add usage function and check for argument

[Boqun Feng <boqun.feng@xxxxxxxxx>]

From: Bhaskar Chowdhury <unixbhaskar@xxxxxxxxx>

This commit converts extract-stall.sh script's header comment to a
usage() function, and adds an argument check.  While in the area, make
this script be executable.

[ paulmck: Strength argument check, remove extraneous comment. ]

Signed-off-by: Bhaskar Chowdhury <unixbhaskar@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
---
 tools/rcu/extract-stall.sh | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)
 mode change 100644 => 100755 tools/rcu/extract-stall.sh

diff --git a/tools/rcu/extract-stall.sh b/tools/rcu/extract-stall.sh
old mode 100644
new mode 100755
index e565697c9f90..08a39ad44320
--- a/tools/rcu/extract-stall.sh
+++ b/tools/rcu/extract-stall.sh
@@ -1,11 +1,25 @@
 #!/bin/sh
 # SPDX-License-Identifier: GPL-2.0+
-#
-# Extract any RCU CPU stall warnings present in specified file.
-# Filter out clocksource lines.  Note that preceding-lines excludes the
-# initial line of the stall warning but trailing-lines includes it.
-#
-# Usage: extract-stall.sh dmesg-file [ preceding-lines [ trailing-lines ] ]
+
+usage() {
+	echo Extract any RCU CPU stall warnings present in specified file.
+	echo Filter out clocksource lines.  Note that preceding-lines excludes the
+	echo initial line of the stall warning but trailing-lines includes it.
+	echo
+	echo Usage: $(basename $0) dmesg-file [ preceding-lines [ trailing-lines ] ]
+	echo
+	echo Error: $1
+}
+
+# Terminate the script, if the argument is missing
+
+if test -f "$1" && test -r "$1"
+then
+	:
+else
+	usage "Console log file \"$1\" missing or unreadable."
+	exit 1
+fi
 
 echo $1
 preceding_lines="${2-3}"
-- 
2.39.2