linux-kernel - Re: [PATCH] rds: send: mark expected switch fall-through in rds_rm

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Date:   Tue, 20 Feb 2018 10:42:31 -0800
From:   Santosh Shilimkar <santosh.shilimkar@...cle.com>
To:     "Gustavo A. R. Silva" <garsilva@...eddedor.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, rds-devel@....oracle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rds: send: mark expected switch fall-through in
 rds_rm_size

On 2/20/2018 10:05 AM, Gustavo A. R. Silva wrote:
> Hi Santosh,
> 
> On 02/20/2018 11:54 AM, Santosh Shilimkar wrote:
>> Hi,
>>
>> 2/19/2018 10:10 AM, Gustavo A. R. Silva wrote:
>>> In preparation to enabling -Wimplicit-fallthrough, mark switch cases
>>> where we are expecting to fall through.
>>>
>>> Addresses-Coverity-ID: 1465362 ("Missing break in switch")
>>> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
>>> ---
>>>   net/rds/send.c | 2 ++
>>>   1 file changed, 2 insertions(+)
>>>
>>> diff --git a/net/rds/send.c b/net/rds/send.c
>>> index 028ab59..79d158b 100644
>>> --- a/net/rds/send.c
>>> +++ b/net/rds/send.c
>>> @@ -902,6 +902,8 @@ static int rds_rm_size(struct msghdr *msg, int 
>>> num_sgs)
>>>           case RDS_CMSG_ZCOPY_COOKIE:
>>>               zcopy_cookie = true;
>>> +            /* fall through */
>>> +
>>>           case RDS_CMSG_RDMA_DEST:
>>>           case RDS_CMSG_RDMA_MAP:
>>>               cmsg_groups |= 2;
>>>
>> So coverity greps for commet as "fall through" for
>> -Wimplicit-fallthrough build ?
>>
> 
> No. Basically, Coverity only reports cases in which a break, return or 
> continue statement is missing.
> 
> Now, if the statements I mention above are missing and if you add the 
> following line to your Makefile:
> 
> KBUILD_CFLAGS  += $(call cc-option,-Wimplicit-fallthrough)
>
> You will get a warning if a fall-through comment is missing.
>
That make sense.

>> Adding that comments itself if fine but was curious
>> about it if some one makes a spell error in this
>> comment what happens ;-)
>>
> 
> In this case, Coverity would still report the same "Missing break in 
> switch" error, but you'll get a GCC warning.
> 
Got it. Thanks !!