linux-kernel - Re: [PATCH] b43: fix regression in PIO case

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Message-ID: <4EFA5E9B.8040106@lwfinger.net>
Date:	Tue, 27 Dec 2011 18:11:07 -0600
From:	Larry Finger <Larry.Finger@...inger.net>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
CC:	Rafał Miłecki <zajec5@...il.com>,
	linux-wireless@...r.kernel.org,
	"John W. Linville" <linville@...driver.com>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] b43: fix regression in PIO case

On 12/27/2011 06:00 PM, Guennadi Liakhovetski wrote:
> On Tue, 27 Dec 2011, Larry Finger wrote:
>
>> On 12/27/2011 05:05 PM, Guennadi Liakhovetski wrote:
>>> On Tue, 27 Dec 2011, Rafał Miłecki wrote:
>>>
>>>> W dniu 26 grudnia 2011 18:28 użytkownik Guennadi Liakhovetski
>>>> <g.liakhovetski@....de>   napisał:
>>>>> This patch fixes the regression, introduced by
>>>>>
>>>>> commit 17030f48e31adde5b043741c91ba143f5f7db0fd
>>>>> From: Rafał Miłecki<zajec5@...il.com>
>>>>> Date: Thu, 11 Aug 2011 17:16:27 +0200
>>>>> Subject: [PATCH] b43: support new RX header, noticed to be used in
>>>>> 598.314+ fw
>>>>>
>>>>> in PIO case.
>>>>>
>>>>> Signed-off-by: Guennadi Liakhovetski<g.liakhovetski@....de>
>>>>> ---
>>>>> diff --git a/drivers/net/wireless/b43/pio.c
>>>>> b/drivers/net/wireless/b43/pio.c
>>>>> index ce8a4bd..b64b64c 100644
>>>>> --- a/drivers/net/wireless/b43/pio.c
>>>>> +++ b/drivers/net/wireless/b43/pio.c
>>>>> @@ -617,9 +617,19 @@ static bool pio_rx_frame(struct b43_pio_rxqueue *q)
>>>>>          const char *err_msg = NULL;
>>>>>          struct b43_rxhdr_fw4 *rxhdr =
>>>>>                  (struct b43_rxhdr_fw4 *)wl->pio_scratchspace;
>>>>> +       size_t rxhdr_size = sizeof(*rxhdr);
>>>>>
>>>>>          BUILD_BUG_ON(sizeof(wl->pio_scratchspace)<   sizeof(*rxhdr));
>>>>> -       memset(rxhdr, 0, sizeof(*rxhdr));
>>>>> +       switch (dev->fw.hdr_format) {
>>>>> +       case B43_FW_HDR_410:
>>>>> +       case B43_FW_HDR_351:
>>>>> +               rxhdr_size -= sizeof(rxhdr->format_598) -
>>>>> +                       sizeof(rxhdr->format_351);
>>>>> +               break;
>>>>> +       case B43_FW_HDR_598:
>>>>> +               break;
>>>>> +       }
>>>>> +       memset(rxhdr, 0, rxhdr_size);
>>>>
>>>> Huuh, that's really tricky. Can you just do "normal" conditions as
>>>> Larry suggested, please?
>>>
>>> Sorry? I absolutely see nothing tricky there. Do you think this would look
>>> "less tricky" to you:
>>>
>>> 	switch (dev->fw.hdr_format) {
>>> 	case B43_FW_HDR_410:
>>> 	case B43_FW_HDR_351:
>>> 		rxhdr_size = offsetof(struct b43_rxhdr_fw4,
>>> 					format_351) +
>>> 			sizeof(rxhdr_size->format_351);
>>> 		break;
>>> 	case B43_FW_HDR_598:
>>> 		rxhdr_size = sizeof(*rxhdr);
>>> 		break;
>>> 	}
>>>
>>
>> How about this?
>>
>> Index: wireless-testing-new/drivers/net/wireless/b43/pio.c
>> ===================================================================
>> --- wireless-testing-new.orig/drivers/net/wireless/b43/pio.c
>> +++ wireless-testing-new/drivers/net/wireless/b43/pio.c
>> @@ -617,9 +617,20 @@ static bool pio_rx_frame(struct b43_pio_
>>          const char *err_msg = NULL;
>>          struct b43_rxhdr_fw4 *rxhdr =
>>                  (struct b43_rxhdr_fw4 *)wl->pio_scratchspace;
>> +       size_t rxhdr_size;
>>
>>          BUILD_BUG_ON(sizeof(wl->pio_scratchspace)<  sizeof(*rxhdr));
>> -       memset(rxhdr, 0, sizeof(*rxhdr));
>> +       switch (dev->fw.hdr_format) {
>> +       case B43_FW_HDR_410:
>> +       case B43_FW_HDR_351:
>> +               rxhdr_size = sizeof(rxhdr->format_351);
>> +               break;
>> +       case B43_FW_HDR_598:
>> +       default:
>> +               rxhdr_size = sizeof(rxhdr->format_598);
>> +               break;
>> +       }
>> +       memset(rxhdr, 0, rxhdr_size);
>>
>>          /* Check if we have data and wait for it to get ready. */
>>          if (q->rev>= 8) {
>
> I am sorry, I'm either being blind and stupid or you're trying to do
> something quite wrong there. struct b43_rxhdr_fw4 has a bunch of fields
> first, then at the end it has a union of two fields: format_598 and
> format_351, right? rxhdr is pointing at the struct itself. Before the
> offending patch memset() used to clean the whole struct. Now in your above
> version you calculate the size of one of those union fields and nullify
> that many bytes from the _beginning_ of the whole struct.
>
> I've seen myself being wrong before, but here... I'll let you judge
> though.

No, you are right. I misread the code. Your patch above would work and is 
probably as clean as one can expect.

Larry


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