linux-kernel - Re: [PATCH 2/2] dma-mapping: benchmark: Add padding to ensure uABI remained consistent

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Message-ID: <c7f7d9b3-2ab3-4ebd-99fb-071733573291@huawei.com>
Date: Thu, 24 Jul 2025 17:35:16 +0800
From: Qinxin Xia <xiaqinxin@...wei.com>
To: Barry Song <21cnbao@...il.com>, <m.szyprowski@...sung.com>
CC: <robin.murphy@....com>, <jonathan.cameron@...wei.com>,
	<prime.zeng@...wei.com>, <fanghao11@...wei.com>,
	<linux-kernel@...r.kernel.org>, <linuxarm@...wei.com>,
	<iommu@...ts.linux.dev>
Subject: Re: [PATCH 2/2] dma-mapping: benchmark: Add padding to ensure uABI
 remained consistent



On 2025/7/24 17:07:08, Barry Song <21cnbao@...il.com> wrote:
> On Thu, Jul 24, 2025 at 4:56 PM 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>
> 
> I don’t think these two patches should be part of the same series. This
> one is a bug fix and should be handled separately—ideally picked up on
> its own and backported to stable.
> 
> Also, the subject should not say "Add"—it should be "Restore". I assume
> Marek can handle it?
> 
>> ---
>>   include/linux/map_benchmark.h | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/include/linux/map_benchmark.h b/include/linux/map_benchmark.h
>> index 62674c83bde4..2ac2fe52f248 100644
>> --- a/include/linux/map_benchmark.h
>> +++ b/include/linux/map_benchmark.h
>> @@ -27,5 +27,6 @@ struct map_benchmark {
>>          __u32 dma_dir; /* DMA data direction */
>>          __u32 dma_trans_ns; /* time for DMA transmission in ns */
>>          __u32 granule;  /* how many PAGE_SIZE will do map/unmap once a time */
>> +       __u8 expansion[76];     /* For future use */
>>   };
>>   #endif /* _KERNEL_DMA_BENCHMARK_H */
>> --
>> 2.33.0
>>
> 
> Thanks
> Barry

Ok, I will send a new version to fix it.
Thanks