selftests/zram: Skip max_comp_streams interface on newer kernel

Since commit 43209ea2d1 ("zram: remove max_comp_streams internals"), zram
has switched to per-cpu streams. Even kernel still keep this interface for
some reasons, but writing to max_comp_stream doesn't take any effect. So
skip it on newer kernel ie 4.7.

The code that comparing kernel version is from xfstests testsuite ext4/053.

Signed-off-by: Yang Xu <xuyang2018.jy@fujitsu.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/zram/zram_lib.sh

@@ -11,6 +11,9 @@ dev_mounted=-1
 
 # Kselftest framework requirement - SKIP code is 4.
 ksft_skip=4
+kernel_version=`uname -r | cut -d'.' -f1,2`
+kernel_major=${kernel_version%.*}
+kernel_minor=${kernel_version#*.}
 
 trap INT
 
@@ -25,6 +28,20 @@ check_prereqs()
 	fi
 }
 
+kernel_gte()
+{
+	major=${1%.*}
+	minor=${1#*.}
+
+	if [ $kernel_major -gt $major ]; then
+		return 0
+	elif [[ $kernel_major -eq $major && $kernel_minor -ge $minor ]]; then
+		return 0
+	fi
+
+	return 1
+}
+
 zram_cleanup()
 {
 	echo "zram cleanup"
@@ -86,6 +103,13 @@ zram_max_streams()
 {
 	echo "set max_comp_streams to zram device(s)"
 
+	kernel_gte 4.7
+	if [ $? -eq 0 ]; then
+		echo "The device attribute max_comp_streams was"\
+		               "deprecated in 4.7"
+		return 0
+	fi
+
 	local i=0
 	for max_s in $zram_max_streams; do
 		local sys_path="/sys/block/zram${i}/max_comp_streams"