KVM: selftests: Add "-c" parameter to dirty log test

It's only used to override the existing dirty ring size/count.  If
with a bigger ring count, we test async of dirty ring.  If with a
smaller ring count, we test ring full code path.  Async is default.

It has no use for non-dirty-ring tests.
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20201001012241.6208-1-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/dirty_log_test.c

@@ -183,6 +183,7 @@ static enum log_mode_t host_log_mode_option = LOG_MODE_ALL;
 /* Logging mode for current run */
 static enum log_mode_t host_log_mode;
 static pthread_t vcpu_thread;
+static uint32_t test_dirty_ring_count = TEST_DIRTY_RING_COUNT;
 
 static void vcpu_kick(void)
 {
@@ -257,7 +258,7 @@ static void dirty_ring_create_vm_done(struct kvm_vm *vm)
 	 * Switch to dirty ring mode after VM creation but before any
 	 * of the vcpu creation.
 	 */
-	vm_enable_dirty_ring(vm, TEST_DIRTY_RING_COUNT *
+	vm_enable_dirty_ring(vm, test_dirty_ring_count *
 			     sizeof(struct kvm_dirty_gfn));
 }
 
@@ -279,7 +280,7 @@ static uint32_t dirty_ring_collect_one(struct kvm_dirty_gfn *dirty_gfns,
 	uint32_t count = 0;
 
 	while (true) {
-		cur = &dirty_gfns[*fetch_index % TEST_DIRTY_RING_COUNT];
+		cur = &dirty_gfns[*fetch_index % test_dirty_ring_count];
 		if (!dirty_gfn_is_dirtied(cur))
 			break;
 		TEST_ASSERT(cur->slot == slot, "Slot number didn't match: "
@@ -803,6 +804,9 @@ static void help(char *name)
 	printf("usage: %s [-h] [-i iterations] [-I interval] "
 	       "[-p offset] [-m mode]\n", name);
 	puts("");
+	printf(" -c: specify dirty ring size, in number of entries\n");
+	printf("     (only useful for dirty-ring test; default: %"PRIu32")\n",
+	       TEST_DIRTY_RING_COUNT);
 	printf(" -i: specify iteration counts (default: %"PRIu64")\n",
 	       TEST_HOST_LOOP_N);
 	printf(" -I: specify interval in ms (default: %"PRIu64" ms)\n",
@@ -858,8 +862,11 @@ int main(int argc, char *argv[])
 	guest_mode_init(VM_MODE_P40V48_4K, true, true);
 #endif
 
-	while ((opt = getopt(argc, argv, "hi:I:p:m:M:")) != -1) {
+	while ((opt = getopt(argc, argv, "c:hi:I:p:m:M:")) != -1) {
 		switch (opt) {
+		case 'c':
+			test_dirty_ring_count = strtol(optarg, NULL, 10);
+			break;
 		case 'i':
 			iterations = strtol(optarg, NULL, 10);
 			break;