btrfs-progs: tests: add helper to compare kernel versions

Return succcess if runnning kernel >= parameter. Most callers will want
to skip the test.

Signed-off-by: David Sterba <dsterba@suse.com>

tests/common

@@ -550,6 +550,28 @@ check_min_kernel_version()
 	return 0
 }
 
+# compare running kernel version to the given parameter, return success
+# if running is newer than requested (let caller decide if to fail or skip)
+# $1: minimum version of running kernel in major.minor format (eg. 4.19)
+check_min_kernel_version()
+{
+	local unamemajor
+	local unameminor
+	local argmajor
+	local argminor
+
+	# 4.19.1-1-default
+	uname=$(uname -r)
+	# 4.19.1
+	uname=${uname%%-*}
+	IFS=. read unamemajor unameminor tmp <<< "$uname"
+	IFS=. read argmajor argminor tmp <<< "$1"
+	# "compare versions: ${unamemajor}.${unameminor} ? ${argmajor}.${argminor}"
+	[ "$unamemajor" -ge "$argmajor" ] || return 1
+	[ "$unameminor" -ge "$argminor" ] || return 1
+	return 0
+}
+
 # how many files to create.
 DATASET_SIZE=50