Re: [RESEND PATCH v4 1/4] dma-mapping: benchmark: Add padding to ensure uABI remained consistent

[Barry Song]

On Mon, Jun 16, 2025 at 9:53 PM Jonathan Cameron
<Jonathan.Cameron@xxxxxxxxxx> wrote:
>
> On Sat, 14 Jun 2025 22:34:51 +0800
> Qinxin Xia <xiaqinxin@xxxxxxxxxx> wrote:
>
> > The padding field in the structure was previously reserved to
> > maintain a stable interface for potential new fields, ensuring
> > compatibility with user-space shared data structures.
> > However,it was accidentally removed by tiantao in a prior commit,
> > which may lead to incompatibility between user space and the kernel.
> >
> > This patch reinstates the padding to restore the original structure
> > layout and preserve compatibility.
> >
> > Fixes: 8ddde07a3d28 ("dma-mapping: benchmark: extract a common header file for map_benchmark definition")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Acked-by: Barry Song <baohua@xxxxxxxxxx>
> > Signed-off-by: Qinxin Xia <xiaqinxin@xxxxxxxxxx>
>
> FWIW I checked the patch above indeed accidentally dropped the padding and the structure
> is copied to userspace so this fix is correct.  Given it's not in a uapi header this
> only really affects the selftest I think this is mostly a case of there possibly being
> out of tree tools with a local copy of this structure definition.

Somehow, I feel we have placed
tools/testing/selftests/dma/dma_map_benchmark.c in the wrong location.
As a selftest, it should have a mechanism to check kernel dependencies,
start properly and automatically, and report pass or fail.

dma_map_benchmark.c seems more like a tool that belongs in tools/dma,
rather than a test.

>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>

Thanks
Barry