Re: [PATCH 1/2] include: uapi: scsi: Change utp_upiu_query struct

From: Bart Van Assche <bvanassche@acm.org>
To: Arthur Simchaev <Arthur.Simchaev@wdc.com>,
	"martin.petersen@oracle.com" <martin.petersen@oracle.com>
Cc: "beanhuo@micron.com" <beanhuo@micron.com>,
	"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] include: uapi: scsi: Change utp_upiu_query struct
Date: Wed, 1 Mar 2023 10:44:06 -0800	[thread overview]
Message-ID: <e6518637-4e78-3935-133d-79afea67cf80@acm.org> (raw)
In-Reply-To: <BY5PR04MB632701F87296BEE554D3F055EDAD9@BY5PR04MB6327.namprd04.prod.outlook.com>

On 3/1/23 01:46, Arthur Simchaev wrote:
>>>>>    struct utp_upiu_query {
>>>>>      __u8 opcode;
>>>>>      __u8 idn;
>>>>>      __u8 index;
>>>>>      __u8 selector;
>>>>> -   __be16 reserved_osf;
>>>>> -   __be16 length;
>>>>> -   __be32 value;
>>>>> -   __be32 reserved[2];
>>>>> +   __u8 osf3;
>>>>> +   __u8 osf4;
>>>>> +   __be16 osf5;
>>>>> +   __be32 osf6;
>>>>> +   __be32 osf7;
>>>>>    };
>>>> All changes in UAPI headers must be backwards compatible. The above
>> doesn't look like a backwards compatible change to me.
>>>
>>> This API was originally invented to support ufs-bsg.
>>> AFAIK, ufs-utils is the only app that makes use of this API,
>>> and it doesn't dig into struct utp_upiu_query inner fields.
>>
>> That does not match what I see. I see that code in ufs-utils accesses
>> the 'length' and 'value' members of the above data structure.
>>
>> Please follow the rules for UAPI header files.
>>
>> Thanks,
>>
>> Bart.
> 
> You are right , my fault.
> Anyway, It just return reserved field to the struct.
> Also I can update the tool accordingly. Instead length and value fields,
> using osf5 and osf6.
> In this case we will keep it backward compatible.
> Is it OK?

Hi Arthur,

I doubt that renaming structure members is acceptable for UAPI headers. 
How about introducing a second struct next to the utp_upiu_query struct?

Thanks,

Bart.