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To: Shreyansh Jain <shreyansh.jain@nxp.com>, dev@dpdk.org
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 <1473257297-7221-2-git-send-email-shreyansh.jain@nxp.com>
Cc: hemant.agrawal@nxp.com, Jan Viktorin <viktorin@rehivetech.com>
From: Ferruh Yigit <ferruh.yigit@intel.com>
Message-ID: <37d34b1e-732e-d31e-a24d-84d4839fe0c5@intel.com>
Date: Thu, 8 Sep 2016 15:16:34 +0100
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Subject: Re: [dpdk-dev] [PATCH v9 01/25] eal: define macro container_of
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On 9/7/2016 3:07 PM, Shreyansh Jain wrote:
> Signed-off-by: Jan Viktorin <viktorin@rehivetech.com>
> Signed-off-by: Shreyansh Jain <shreyansh.jain@nxp.com>
> ---
>  lib/librte_eal/common/include/rte_common.h | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/lib/librte_eal/common/include/rte_common.h b/lib/librte_eal/common/include/rte_common.h
> index 332f2a4..c5d94f3 100644
> --- a/lib/librte_eal/common/include/rte_common.h
> +++ b/lib/librte_eal/common/include/rte_common.h
> @@ -322,6 +322,27 @@ 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);
> + *
> + * Some implementation already have this defined, thus, conditional
> + * declaration.
> + */
> +#ifndef container_of
> +#define container_of(p, type, member) \
> +	((type *) (((char *) (p)) - offsetof(type, member)))
> +#endif
> +
>  #define _RTE_STR(x) #x
>  /** Take a macro value and get a string version of it */
>  #define RTE_STR(x) _RTE_STR(x)
> 

Some mlx5 files includes dpdk version of container_of first, they
produce following warning:

In file included from .../dpdk/build/include/rte_mbuf.h:57:0,
                 from .../dpdk/build/include/rte_ether.h:52,
                 from .../dpdk/drivers/net/mlx5/mlx5_trigger.c:38:
/usr/include/infiniband/verbs.h: In function ‘verbs_get_device’:
.../dpdk/build/include/rte_common.h:343:14: warning: cast discards
‘const’ qualifier from pointer target type [-Wcast-qual]
  ((type *) (((char *) (p)) - offsetof(type, member)))

The verbs.h version of container_of is same with dpdk one, I am not able
to find why one gives warning but other not.

Regards,
ferruh