The gup_test binary will fail showing only the output of perror("open") in the case that /sys/kernel/debug/gup_test is not found. This will almost always be due to CONFIG_GUP_TEST not being set, which enables compilation of a kernel that provides this file.

Add a short error message to clarify this failure and point the user to the solution.

Signed-off-by: Joel Savitz jsavitz@redhat.com --- tools/testing/selftests/vm/gup_test.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/vm/gup_test.c b/tools/testing/selftests/vm/gup_test.c index cda837a14736..ac4e804d47f0 100644 --- a/tools/testing/selftests/vm/gup_test.c +++ b/tools/testing/selftests/vm/gup_test.c @@ -18,6 +18,8 @@ #define FOLL_WRITE 0x01 /* check pte is writable */ #define FOLL_TOUCH 0x02 /* mark page accessed */

+#define GUP_TEST_FILE "/sys/kernel/debug/gup_test" + static unsigned long cmd = GUP_FAST_BENCHMARK; static int gup_fd, repeats = 1; static unsigned long size = 128 * MB; @@ -204,9 +206,11 @@ int main(int argc, char **argv) if (write) gup.gup_flags |= FOLL_WRITE;

- gup_fd = open("/sys/kernel/debug/gup_test", O_RDWR); + gup_fd = open(GUP_TEST_FILE, O_RDWR); if (gup_fd == -1) { perror("open"); + fprintf(stderr, "Unable to open %s: check that CONFIG_GUP_TEST=y\n", + GUP_TEST_FILE); exit(1); }