linux-kernel - Re: [PATCH 8/8] staging: rtl8188eu: use is_broadcast_ether

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Message-ID: <85e40925-21aa-1030-24ed-9dce498b98f6@gmail.com>
Date:   Sun, 29 Jul 2018 20:21:22 +0200
From:   Michael Straube <straube.linux@...il.com>
To:     Joe Perches <joe@...ches.com>, gregkh@...uxfoundation.org
Cc:     devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 8/8] staging: rtl8188eu: use is_broadcast_ether_addr

On 07/29/18 19:59, Joe Perches wrote:
> On Sun, 2018-07-29 at 19:42 +0200, Michael Straube wrote:
>> On 07/29/18 19:21, Joe Perches wrote:
>>> On Sun, 2018-07-29 at 19:08 +0200, Michael Straube wrote:
>>>> Use is_broadcast_ether_addr instead of checking each byte of the
>>>> address array for 0xff. Shortens the code and improves readability.
>>>
>>> You should show in the commit log that sta_addr is __aligned(2)
>>> as required by is_broadcast_ether_addr, otherwise you could be
>>> introducing runtime alignment defects.
>>>
>>
>> Ok, sta_addr is used from following structs.
>>
>> struct ieee_param {
>>           u32 cmd;
>>           u8 sta_addr[ETH_ALEN];
>>           union {
>>           ...
>>           ...
>>           }; u
>> };
>>
>> struct ieee_param_ex {
>> 	u32 cmd;
>> 	u8 sta_addr[ETH_ALEN];
>> 	u8 data[0];
>> };
>>
>> Well, looking at it now, I'm not sure about the alignment anymore
>> in the struct that contains the union. Is sta_addr in the first
>> struct __aligned(2)?
>>
>> Should I include the snippets in the commit message, or is just
>> writing that sta_addr is __aligned(2) enough? (if it is in the
>> first case...)
> 
> It's enough to just state that the uses are properly aligned
> as long as you looked and understand that it's required.
> 

Ok, thank you.

I looked at it and understand that it's required.
But, as mentioned, at second look I'm not sure about the union.

I guess I need to read a little more about the alignment of unions.
Any hints are welcomed. :)

Michael