Re: [PATCH] Staging: rtl8723au: os_intfs: fixed case statement is variable issue

sunbing
2016-08-13T09:26:59Z

On Aug 12, 2016, at 22:30, Jes Sorensen <Jes.Sorensen@redhat.com> wrote:

> sunbing <sunbing@redflag-linux.com> writes:
>> On Aug 11, 2016, at 23:25, Jes Sorensen <Jes.Sorensen@redhat.com> wrote:
>>
>>> Bing Sun <sunbing@redflag-linux.com> writes:
>>>> Fixed sparse parse error:
>>>> Expected constant expression in case statement.
>>>>
>>>> Signed-off-by: Bing Sun <sunbing@redflag-linux.com>
>>>> ---
>>>> drivers/staging/rtl8723au/os_dep/os_intfs.c | 11 +++++------
>>>> 1 file changed, 5 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/drivers/staging/rtl8723au/os_dep/os_intfs.c b/drivers/staging/rtl8723au/os_dep/os_intfs.c
>>>> index b8848c2..f30d5d2 100644
>>>> --- a/drivers/staging/rtl8723au/os_dep/os_intfs.c
>>>> +++ b/drivers/staging/rtl8723au/os_dep/os_intfs.c
>>>> @@ -283,14 +283,13 @@ static u32 rtw_classify8021d(struct sk_buff *skb)
>>>> */
>>>> if (skb->priority >= 256 && skb->priority <= 263)
>>>> return skb->priority - 256;
>>>> - switch (skb->protocol) {
>>>> - case htons(ETH_P_IP):
>>>> +
>>>> + if (skb->protocol == htons(ETH_P_IP)) {
>>>> dscp = ip_hdr(skb)->tos & 0xfc;
>>>> - break;
>>>> - default:
>>>> - return 0;
>>>> + return dscp >> 5;
>>>> }
>>>> - return dscp >> 5;
>>>> +
>>>> + return 0;
>>>> }
>>>
>>> Pardon me here, but I find it really hard to see how this change is an
>>> improvement over the old code in any shape or form.
>>>
>>> Jes
>>
>> There is no functional improvement.
>> But before this patch, when we do: make C=1 M=drivers/staging/rtl8723au/
>> An error output:
>> drivers/staging/rtl8723au//os_dep/os_intfs.c:287:14: error: Expected
>> constant expression in case statement
>> To avoid sparse parse error, a case statement converts to an if statement.
>> So we got this patch.
>
> Hello
>
> I understand this part, but it seems to me we are changing the code due
> to a broken test case in sparse. Does the warning go away if you use
> __constant_htons() instead of htons()?
>
> Jes

Thanks for your guidance.

1. If I use __constant_htons, checkpatch.pl will warning:
WARNING: __constant_htons should be htons

2. In os_intfs.c: rtw_classify8021d, there are only one case statement and a
default statement. So, convert "switch case" to "if else" is more readable in my opinion.

So, I pushed this patch.

There are some patches convert use of __constant_htons to htons in kernel logs.
Will there be a new patch convert to htons in the future if I use __constant_htons now ?

After search through kernel code, there are 158 "case htons(...)" statements and
2 "case __constant_htons(...)" statements. Does this mean we can ignore sparse
error and use "case htons(...)" ?

It makes me confused. More help, please.

Regards.