selftests/ftrace: Quote check_requires comparisons

check_requires() compares requirement strings that can contain shell
pattern characters such as '[' and ']'. Under /bin/sh, the unquoted
test expressions can emit 'unexpected operator' warnings while parsing
README-backed requirements.

Quote the relevant comparisons and path checks so the helper handles
those patterns without spurious shell warnings.

Validated by rerunning fprobe_syntax_errors.tc and confirming the
previous '/bin/sh: unexpected operator' lines disappear from the
detailed ftracetest log.

Signed-off-by: Cao Ruichuang <create0818@163.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20260408043212.8063-1-create0818@163.com
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Author: RichardCao

tools/testing/selftests/ftrace/test.d/functions

@@ -145,13 +145,13 @@ check_requires() { # Check required files and tracers
 	p=${i%:program}
         r=${i%:README}
         t=${i%:tracer}
-	if [ $p != $i ]; then
-	    if ! which $p ; then
+	if [ "$p" != "$i" ]; then
+	    if ! which "$p" ; then
                 echo "Required program $p is not found."
                 exit_unresolved
 	    fi
-        elif [ $t != $i ]; then
-            if ! grep -wq $t available_tracers ; then
+        elif [ "$t" != "$i" ]; then
+            if ! grep -wq "$t" available_tracers ; then
                 echo "Required tracer $t is not configured."
                 exit_unsupported
             fi
@@ -162,11 +162,11 @@ check_requires() { # Check required files and tracers
 	    else
 		test=$TRACING_DIR
 	    fi
-            if ! grep -Fq "$r" $test/README ; then
+            if ! grep -Fq "$r" "$test"/README ; then
                 echo "Required feature pattern \"$r\" is not in README."
                 exit_unsupported
             fi
-        elif [ ! -e $i ]; then
+        elif [ ! -e "$i" ]; then
             echo "Required feature interface $i doesn't exist."
             exit_unsupported
         fi
@@ -227,4 +227,4 @@ get_mnt_options() {
 	local opts=$(mount | grep -m1 "$mnt_point" | sed -e 's/.*(\(.*\)).*/\1/')
 
 	echo "$opts"
-}
+}