Re: [PATCH net] selftests: drv-net: devmem: Skip when hugetlbfs isn't supported

["Björn Töpel" <bjorn@kernel.org>]

Maxime Chevallier <maxime.chevallier@bootlin.com> writes:

> The devmem selftest requires accessing /proc/sys/vm/nr_hugepages,
> which is only available when hugetlbfs is supported. This isn't the
> case on all CPU architectures, for example it isn't supported on ARM
> 32-bits on cores that don't support LPAE.
>
> On these devices, the devmem kselftest doesn't skip gracefully, it hits
> an exception while trying to open the nr_hugepages file :
>
>   # Exception|     _reserve_hugepages()
>   # Exception|     ~~~~~~~~~~~~~~~~~~^^
>   # Exception|   File "/usr/lib/kselftests/drivers/net/hw/devmem_lib.py", line 36, in _reserve_hugepages
>   # Exception|     with open(NR_HUGEPAGES_FILE, 'r+', encoding='utf-8') as f:
>   # Exception|          ~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>   # Exception| FileNotFoundError: [Errno 2] No such file or directory: '/proc/sys/vm/nr_hugepages'
>
> Let's check if the file exists before trying to open it, and return
> immediately if we can't.
>
> The _reserve_hugepages() runs as part of the "require_devmem()", that
> skips if devmem itself isn't supported. Before the blamed commit, this
> check was done prior to accessing nr_hugepages, so the problem wasn't
> showing.
>
> This has been found by trying to run the selftest on stmmac, on an
> Altera CycloneV SoC (Cortex A9, doesn't support hugepages).
>
> Fixes: 8ac4255c1e0c ("selftests/net: devmem.py: add check_rx_large_niov")
> Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
> ---
>  tools/testing/selftests/drivers/net/hw/devmem_lib.py | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/tools/testing/selftests/drivers/net/hw/devmem_lib.py b/tools/testing/selftests/drivers/net/hw/devmem_lib.py
> index 3554954a6691..24637fb180ca 100644
> --- a/tools/testing/selftests/drivers/net/hw/devmem_lib.py
> +++ b/tools/testing/selftests/drivers/net/hw/devmem_lib.py
> @@ -33,6 +33,8 @@ def _restore_nr_hugepages(nr_hugepages):
>  
>  def _reserve_hugepages(want=64):
>      """Raise nr_hugepages to @want and arrange for it to be restored."""
> +    if not os.path.exists(NR_HUGEPAGES_FILE):
> +        return

Maybe raise a KsftSkipEx() would be more robust? No biggie...

Reviewed-by: Björn Töpel <bjorn@kernel.org>