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SubjectRe: [PATCH] staging: gdm724x: Add parenthesis to Macro arguments
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Hi Greg, thanks for replying.

On 03/04/2019 01:26, Greg KH wrote:
> On Tue, Apr 02, 2019 at 10:04:05PM -0300, Andre Dainez wrote:
>> Fix checkpatch errors:
>>
>> CHECK: Macro argument 'len' may be better as '(len)' to avoid precedence issues
>> CHECK: Macro argument 'nlh' may be better as '(nlh)' to avoid precedence issues
>>
>> Signed-off-by: Andre Dainez <andredainez@gmail.com>
>> ---
>> drivers/staging/gdm724x/netlink_k.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/staging/gdm724x/netlink_k.c b/drivers/staging/gdm724x/netlink_k.c
>> index 92440c3..36d88f4 100644
>> --- a/drivers/staging/gdm724x/netlink_k.c
>> +++ b/drivers/staging/gdm724x/netlink_k.c
>> @@ -19,8 +19,8 @@ static DEFINE_MUTEX(netlink_mutex);
>> #define ND_NLMSG_SPACE(len) (NLMSG_SPACE(len) + ND_IFINDEX_LEN)
>> #define ND_NLMSG_DATA(nlh) ((void *)((char *)NLMSG_DATA(nlh) + \
>> ND_IFINDEX_LEN))
>> -#define ND_NLMSG_S_LEN(len) (len + ND_IFINDEX_LEN)
>> -#define ND_NLMSG_R_LEN(nlh) (nlh->nlmsg_len - ND_IFINDEX_LEN)
>> +#define ND_NLMSG_S_LEN(len) ((len) + ND_IFINDEX_LEN)
>
> This makes sense, but:
>
>> +#define ND_NLMSG_R_LEN(nlh) ((nlh)->nlmsg_len - ND_IFINDEX_LEN)
>
> That does not, correct?
>
Could you please clarify why this doesn't make sense?
If, for some reason I calculate by hand the pointer address and call this macro like:
ND_NLMSG_R_LEN(nlh + sizeof(*nlh)),
then it would expand like nlh + sizeof(*nlh)->nlmsg_len - ND_IFINDEX_LEN
which looks wrong in my pov, no?

Please, let me know if I misunderstood anything.
Thanks

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