[dpdk-dev] [PATCH v9 01/25] eal: define macro container_of

Adrien Mazarguil adrien.mazarguil at 6wind.com
Fri Sep 9 10:55:37 CEST 2016


On Fri, Sep 09, 2016 at 09:49:06AM +0530, Shreyansh Jain wrote:
> Hi Ferruh,
> 
> On Thursday 08 September 2016 07:46 PM, Ferruh Yigit wrote:
> >On 9/7/2016 3:07 PM, Shreyansh Jain wrote:
> >>Signed-off-by: Jan Viktorin <viktorin at rehivetech.com>
> >>Signed-off-by: Shreyansh Jain <shreyansh.jain at 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.
> 
> Thanks for highlighting. I am setting up my environment and will have a
> look.

This warning is a known issue in the Verbs header that will be addressed
eventually. It occurs even without Shreyansh's patch (more likely when
CONFIG_RTE_LIBRTE_MLX4_DEBUG and/or CONFIG_RTE_LIBRTE_MLX5_DEBUG are
enabled).

Your container_of() macro is fine, no need to spend time on this.

-- 
Adrien Mazarguil
6WIND


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