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

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Message-ID: <CAGsJ_4wOB+cmGzuzzacwJGeUYgGLuKg94wuWC+mA-_=r0TVuhQ@mail.gmail.com>
Date: Mon, 16 Jun 2025 22:40:38 +1200
From: Barry Song <21cnbao@...il.com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: Qinxin Xia <xiaqinxin@...wei.com>, m.szyprowski@...sung.com, robin.murphy@....com, 
	yangyicong@...wei.com, hch@....de, iommu@...ts.linux.dev, 
	prime.zeng@...wei.com, fanghao11@...wei.com, linux-kernel@...r.kernel.org, 
	linuxarm@...wei.com
Subject: Re: [RESEND PATCH v4 1/4] dma-mapping: benchmark: Add padding to
 ensure uABI remained consistent

On Mon, Jun 16, 2025 at 9:53 PM Jonathan Cameron
<Jonathan.Cameron@...wei.com> wrote:
>
> On Sat, 14 Jun 2025 22:34:51 +0800
> Qinxin Xia <xiaqinxin@...wei.com> 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@...r.kernel.org
> > Acked-by: Barry Song <baohua@...nel.org>
> > Signed-off-by: Qinxin Xia <xiaqinxin@...wei.com>
>
> 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@...wei.com>

Thanks
Barry