Re: [dpdk-dev] [PATCH v2 1/8] eal: define container_of macro

[Shreyansh Jain <shreyansh.jain@nxp.com>]

On Thursday 08 December 2016 12:31 PM, Shreyansh Jain wrote:
> Hello Jan,
>
> Need your help in resolving the checkpatch issue for this patch.
> I have used this in EAL Bus series [1].
>
> [1] http://dpdk.org/ml/archives/dev/2016-December/051350.html
>
> On Monday 21 November 2016 10:25 PM, Jan Blunck wrote:
>> This macro is based on Jan Viktorin's original patch but also checks the
>> type of the passed pointer against the type of the member.
>>
>> Signed-off-by: Jan Viktorin <viktorin@rehivetech.com>
>> Signed-off-by: Shreyansh Jain <shreyansh.jain@nxp.com>
>> [jblunck@infradead.org: add type checking and __extension__]
>> Signed-off-by: Jan Blunck <jblunck@infradead.org>
>> ---
>>  lib/librte_eal/common/include/rte_common.h | 20 ++++++++++++++++++++
>>  1 file changed, 20 insertions(+)
>>
>> diff --git a/lib/librte_eal/common/include/rte_common.h
>> b/lib/librte_eal/common/include/rte_common.h
>> index db5ac91..8dda3e2 100644
>> --- a/lib/librte_eal/common/include/rte_common.h
>> +++ b/lib/librte_eal/common/include/rte_common.h
>> @@ -331,6 +331,26 @@ rte_bsf32(uint32_t v)
>>  #define offsetof(TYPE, MEMBER)  __builtin_offsetof (TYPE, MEMBER)
>>  #endif
>>
>> +/**
>> + * Return pointer to the wrapping struct instance.
>> + *
>> + * Example:
>> + *
>> + *  struct wrapper {
>> + *      ...
>> + *      struct child c;
>> + *      ...
>> + *  };
>> + *
>> + *  struct child *x = obtain(...);
>> + *  struct wrapper *w = container_of(x, struct wrapper, c);
>> + */
>> +#ifndef container_of
>> +#define container_of(ptr, type, member)    __extension__ ({        \
>> +            typeof(((type *)0)->member) *_ptr = (ptr);    \
>> +            (type *)(((char *)_ptr) - offsetof(type, member)); })
>> +#endif
>
> (I think there was discussion in ML about this but where, I couldn't
> find it).
>
> Above code snippet doesn't go down well with the checkpatch script. It
> reports:
>
> ---->8----
> ERROR:COMPLEX_MACRO: Macros with complex values should be enclosed in
> parentheses
> #40: FILE: lib/librte_eal/common/include/rte_common.h:349:
> +#define container_of(ptr, type, member)        __extension__ ({        \
> +                       typeof(((type *)0)->member) *_ptr = (ptr);      \
> +                       (type *)(((char *)_ptr) - offsetof(type,
> member)); })
>
> ERROR:SPACING: need consistent spacing around '*' (ctx:WxV)
> #41: FILE: lib/librte_eal/common/include/rte_common.h:350:
> +                       typeof(((type *)0)->member) *_ptr = (ptr);      \
> ---->8----
>
> Second error is primarily because of '*<space>_ptr' rather than '*_ptr'.
>
> Is do{ ... }while(0) the fix for the first one?
>
> This:
>
> ---->8----
> #ifndef container_of
> #define container_of(ptr, type, member) do {                 \
>            __extension__                                     \
>            typeof(((type *)0)->member) * _ptr = (ptr);       \
>            (type *)(((char *)_ptr) - offsetof(type, member));\
>            } while (0)
> #endif
> ---->8----
>
> Seems to be ok with checkpatch. Do you see any technical/compiler issue
> with this?

My bad.
obviously a 'do{ .. } while(0)' will not work in case of assignment.

Any other hints as to how to remove this checkpatch issue?

>
>> +
>>  #define _RTE_STR(x) #x
>>  /** Take a macro value and get a string version of it */
>>  #define RTE_STR(x) _RTE_STR(x)
>>
>
> -
> Shreyansh
>
>
>