[PATCH v7 1/8] selftests/cgroup: skip test_zswap if zswap is globally disabled

[Li Wang <li.wang@linux.dev>]

test_zswap currently only checks whether zswap is present by testing
/sys/module/zswap. This misses the runtime global state exposed in
/sys/module/zswap/parameters/enabled.

When zswap is built/loaded but globally disabled, the zswap cgroup
selftests run in an invalid environment and may fail spuriously.

Check the runtime enabled state before running the tests:
  - skip if zswap is not configured,
  - fail if the enabled knob cannot be read,
  - skip if zswap is globally disabled.

Also print a hint in the skip message on how to enable zswap.

Signed-off-by: Li Wang <li.wang@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Yosry Ahmed <yosry@kernel.org>
Acked-by: Nhat Pham <nphamcs@gmail.com>
---
 tools/testing/selftests/cgroup/test_zswap.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
index a7bdcdd09d6..a94238a2e04 100644
--- a/tools/testing/selftests/cgroup/test_zswap.c
+++ b/tools/testing/selftests/cgroup/test_zswap.c
@@ -15,6 +15,9 @@
 #include "kselftest.h"
 #include "cgroup_util.h"
 
+#define PATH_ZSWAP "/sys/module/zswap"
+#define PATH_ZSWAP_ENABLED "/sys/module/zswap/parameters/enabled"
+
 static int read_int(const char *path, size_t *value)
 {
 	FILE *file;
@@ -725,9 +728,18 @@ struct zswap_test {
 };
 #undef T
 
-static bool zswap_configured(void)
+static void check_zswap_enabled(void)
 {
-	return access("/sys/module/zswap", F_OK) == 0;
+	char value[2];
+
+	if (access(PATH_ZSWAP, F_OK))
+		ksft_exit_skip("zswap isn't configured\n");
+
+	if (read_text(PATH_ZSWAP_ENABLED, value, sizeof(value)) <= 0)
+		ksft_exit_fail_msg("Failed to read " PATH_ZSWAP_ENABLED "\n");
+
+	if (value[0] == 'N')
+		ksft_exit_skip("zswap is disabled (hint: echo 1 > " PATH_ZSWAP_ENABLED ")\n");
 }
 
 int main(int argc, char **argv)
@@ -740,8 +752,7 @@ int main(int argc, char **argv)
 	if (cg_find_unified_root(root, sizeof(root), NULL))
 		ksft_exit_skip("cgroup v2 isn't mounted\n");
 
-	if (!zswap_configured())
-		ksft_exit_skip("zswap isn't configured\n");
+	check_zswap_enabled();
 
 	/*
 	 * Check that memory controller is available:
-- 
2.53.0