On Mon, 2 May 2022 18:49:42 -0400 Joel Savitz <jsavitz@xxxxxxxxxx> wrote:
>
> 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.
>
> --- 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);
> }
>
Sidhartha did a similar thing:
https://lkml.kernel.org/r/20220405214809.3351223-1-sidhartha.kumar@xxxxxxxxxx
(Which is now in mm-stable at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm)
Although in retroreview, it should have printed that to stderr rather
than to stdout.
