Re: [PATCH RESEND v1 1/5] selftests/mm: skip COW tmpfile cases when fallocate() is unsupported

[Sarthak Sharma]

On 7/22/26 2:41 PM, Muhammad Usama Anjum wrote:
> The tmpfile-backed COW cases allocate a one-page file with fallocate()
> before exercising private and shared mappings.  When the filesystem
> backing tmpfile() does not implement fallocate(), setup fails with
> EOPNOTSUPP and no COW behavior is exercised.
> 
> This occurs when the temporary directory resides on a filesystem with
> limited allocation support, such as NFSv3.  Reporting a failure adds
> noise because the test prerequisite is absent rather than the COW
> implementation being broken.
> 
> Report EOPNOTSUPP as a skip.  Continue treating every other fallocate()
> error as a failure so unexpected setup regressions remain visible.
> 
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxx>

I've tested this patch on a QEMU with ramfs mounted over /tmp, which
does not support fallocate().

Before applying the patch, 3 tests (Basic COW with tmpfile, R/O longterm
GUP pin with tmpfile and R/O longterm GUP-fast pin with tmpfile) failed
with
# fallocate() failed: Operation not supported (95)

After applying the patch, these tests are skipped.

Tested-by: Sarthak Sharma <sarthak.sharma@xxxxxxx>

> ---
>  tools/testing/selftests/mm/cow.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/cow.c b/tools/testing/selftests/mm/cow.c
> index 0c627ea89ff7b..c1b8920e29342 100644
> --- a/tools/testing/selftests/mm/cow.c
> +++ b/tools/testing/selftests/mm/cow.c
> @@ -1718,8 +1718,13 @@ static void run_with_tmpfile(non_anon_test_fn fn, const char *desc)
>  
>  	/* File consists of a single page filled with zeroes. */
>  	if (fallocate(fd, 0, 0, pagesize)) {
> -		ksft_perror("fallocate() failed");
> -		log_test_result(KSFT_FAIL);
> +		if (errno == EOPNOTSUPP) {
> +			ksft_print_msg("fallocate() not supported by filesystem\n");
> +			log_test_result(KSFT_SKIP);
> +		} else {
> +			ksft_perror("fallocate() failed");
> +			log_test_result(KSFT_FAIL);
> +		}
>  		goto close;
>  	}
>