[PATCH v2 5/6] userfaultfd: selftests: make /dev/userfaultfd testing configurable

[Axel Rasmussen <axelrasmussen@google.com>]

Instead of always testing both userfaultfd(2) and /dev/userfaultfd,
let the user choose which to test.

As with other test features, change the behavior based on a new
command line flag. Introduce the idea of "test mods", which are
generic (not specific to a test type) modifications to the behavior of
the test. This is sort of borrowed from this RFC patch series [1], but
simplified a bit.

The benefit is, in "typical" configurations this test is somewhat slow
(say, 30sec or something). Testing both clearly doubles it, so it may
not always be desirable, as users are likely to use one or the other,
but never both, in the "real world".

[1]: https://patchwork.kernel.org/project/linux-mm/patch/20201129004548.1619714-14-namit@vmware.com/

Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
---
 tools/testing/selftests/vm/userfaultfd.c | 41 +++++++++++++++++-------
 1 file changed, 30 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
index 12ae742a9981..274522704e40 100644
--- a/tools/testing/selftests/vm/userfaultfd.c
+++ b/tools/testing/selftests/vm/userfaultfd.c
@@ -142,8 +142,17 @@ static void usage(void)
 {
 	fprintf(stderr, "\nUsage: ./userfaultfd <test type> <MiB> <bounces> "
 		"[hugetlbfs_file]\n\n");
+
 	fprintf(stderr, "Supported <test type>: anon, hugetlb, "
 		"hugetlb_shared, shmem\n\n");
+
+	fprintf(stderr, "'Test mods' can be joined to the test type string with a ':'. "
+		"Supported mods:\n");
+	fprintf(stderr, "\tdev - Use /dev/userfaultfd instead of userfaultfd(2)\n");
+	fprintf(stderr, "\nExample test mod usage:\n");
+	fprintf(stderr, "# Run anonymous memory test with /dev/userfaultfd:\n");
+	fprintf(stderr, "./userfaultfd anon:dev 100 99999\n\n");
+
 	fprintf(stderr, "Examples:\n\n");
 	fprintf(stderr, "%s", examples);
 	exit(1);
@@ -1610,8 +1619,6 @@ unsigned long default_huge_page_size(void)
 
 static void set_test_type(const char *type)
 {
-	uint64_t features = UFFD_API_FEATURES;
-
 	if (!strcmp(type, "anon")) {
 		test_type = TEST_ANON;
 		uffd_test_ops = &anon_uffd_test_ops;
@@ -1631,10 +1638,28 @@ static void set_test_type(const char *type)
 		test_type = TEST_SHMEM;
 		uffd_test_ops = &shmem_uffd_test_ops;
 		test_uffdio_minor = true;
-	} else {
-		err("Unknown test type: %s", type);
+	}
+}
+
+static void parse_test_type_arg(const char *raw_type)
+{
+	char *buf = strdup(raw_type);
+	uint64_t features = UFFD_API_FEATURES;
+
+	while (buf) {
+		const char *token = strsep(&buf, ":");
+
+		if (!test_type)
+			set_test_type(token);
+		else if (!strcmp(token, "dev"))
+			test_dev_userfaultfd = true;
+		else
+			err("unrecognized test mod '%s'", token);
 	}
 
+	if (!test_type)
+		err("failed to parse test type argument: '%s'", raw_type);
+
 	if (test_type == TEST_HUGETLB)
 		page_size = default_huge_page_size();
 	else
@@ -1681,7 +1706,7 @@ int main(int argc, char **argv)
 		err("failed to arm SIGALRM");
 	alarm(ALARM_INTERVAL_SECS);
 
-	set_test_type(argv[1]);
+	parse_test_type_arg(argv[1]);
 
 	nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
 	nr_pages_per_cpu = atol(argv[2]) * 1024*1024 / page_size /
@@ -1719,12 +1744,6 @@ int main(int argc, char **argv)
 	}
 	printf("nr_pages: %lu, nr_pages_per_cpu: %lu\n",
 	       nr_pages, nr_pages_per_cpu);
-
-	test_dev_userfaultfd = false;
-	if (userfaultfd_stress())
-		return 1;
-
-	test_dev_userfaultfd = true;
 	return userfaultfd_stress();
 }
 
-- 
2.36.0.rc2.479.g8af0fa9b8e-goog