[LTP] [PATCH v2] syscalls/userfaultfd01: add hint about unprivileged_userfaultfd

[Yang Xu]

Since commit cefdca0a86be ("userfaultfd/sysctl: add vm.unprivileged_userfaultfd").
, it adds a global sysctl knob "vm.unprivileged_userfaultfd" to control whether
unprivileged users can use the userfaultfd system calls. Set this to 1 to allow
unprivileged users to use the userfaultfd system calls, or set this to 0 to
restrict userfaultfd to only privileged users (with SYS_CAP_PTRACE capability). The
default value is 1. Add hint about it.

Signed-off-by: Yang Xu <xuyang2018.jy@cn.fujitsu.com>
---
 .../syscalls/userfaultfd/userfaultfd01.c      | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/testcases/kernel/syscalls/userfaultfd/userfaultfd01.c b/testcases/kernel/syscalls/userfaultfd/userfaultfd01.c
index a5e142209..4e178b4f8 100644
--- a/testcases/kernel/syscalls/userfaultfd/userfaultfd01.c
+++ b/testcases/kernel/syscalls/userfaultfd/userfaultfd01.c
@@ -82,12 +82,19 @@ static void run(void)
 
 	set_pages();
 
-	uffd = sys_userfaultfd(O_CLOEXEC | O_NONBLOCK);
-
-	if (uffd == -1)
-		tst_brk(TBROK | TERRNO,
-			"Could not create userfault file descriptor");
-
+	TEST(sys_userfaultfd(O_CLOEXEC | O_NONBLOCK));
+
+	if (TST_RET == -1) {
+		if (TST_ERR == EPERM) {
+			tst_res(TCONF, "Hint: check /proc/sys/vm/unprivileged_userfaultfd");
+			tst_brk(TCONF | TTERRNO,
+				"userfaultfd() requires CAP_SYS_PTRACE on this system");
+		} else
+			tst_brk(TBROK | TTERRNO,
+				"Could not create userfault file descriptor");
+	}
+
+	uffd = TST_RET;
 	uffdio_api.api = UFFD_API;
 	uffdio_api.features = 0;
 	SAFE_IOCTL(uffd, UFFDIO_API, &uffdio_api);
-- 
2.18.0