[PATCH 18/19] raid6_kunit: randomize parameters and increase limits

[Christoph Hellwig]

The current test has double-quadratic behavior in the selection for
the updated ("XORed") disks, and in the selection of updated pointers,
which makes scaling it to more tests difficult.  At the same time it
only ever tests with the maximum number of disks, which leaves a
coverage hole for smaller ones.

Fix this by randomizing the total number, failed disks and regions
to update, and increasing the upper number of tests disks.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 lib/raid/raid6/tests/raid6_kunit.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/lib/raid/raid6/tests/raid6_kunit.c b/lib/raid/raid6/tests/raid6_kunit.c
index 775a0051f9a4..d6ac777dcaee 100644
--- a/lib/raid/raid6/tests/raid6_kunit.c
+++ b/lib/raid/raid6/tests/raid6_kunit.c
@@ -8,6 +8,7 @@
 #include <kunit/test.h>
 #include <linux/prandom.h>
 #include <linux/vmalloc.h>
+#include <linux/raid/pq.h>
 #include "../algos.h"
 
 MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");
@@ -43,6 +44,12 @@ static unsigned int random_length(unsigned int max_length)
 	return round_up((rand32() % max_length) + 1, 512);
 }
 
+static unsigned int random_nr_buffers(void)
+{
+	return (rand32() % (RAID6_KUNIT_MAX_BUFFERS - (RAID6_MIN_DISKS - 1))) +
+			RAID6_MIN_DISKS;
+}
+
 static void makedata(int start, int stop)
 {
 	int i;
@@ -169,9 +176,7 @@ static void test_rmw(struct kunit *test, unsigned int nr_buffers,
 static void raid6_test_one(struct kunit *test)
 {
 	const struct test_args *ta = test->param_value;
-	/* including P/Q we need at least three buffers */
-	unsigned int nr_buffers =
-		(rand32() % (RAID6_KUNIT_MAX_BUFFERS - 2)) + 3;
+	unsigned int nr_buffers = random_nr_buffers();
 	unsigned int len = random_length(RAID6_KUNIT_MAX_BYTES);
 
 	/* Nuke syndromes */
-- 
2.53.0