[ovs-dev] [PATCH] util: Update OVS_TYPEOF macro for Windows.

Archana Holla harchana at vmware.com
Tue Apr 7 18:28:26 UTC 2020


Thanks Ben for the review comments.
Please find my answers for the questions and could you please take a look at v2 of patch with review commented addressed.

>>Does this solve a problem?
Yes,
  #define OBJECT_CONTAINING(POINTER, OBJECT, MEMBER) \
     ((OVS_TYPEOF(OBJECT)) (void *) \
     ((char *) (POINTER) - OBJECT_OFFSETOF(OBJECT, MEMBER)))
    
  On using ovs macro OBJECT_CONTAINING(which references OVS_TYPEOF), following compilation error is observed on windows C++ application:
  "
  error C2440: '=': cannot convert from 'void *' to 'object *'
  note: Conversion from 'void*' to pointer to non-'void' requires an explicit cast
   "
  With "decltype" keyword, this issue isn't seen as object is type casted to the right type.

>>decltype is a C++ feature.  How is it specific to Windows?
  Agree with the review comment, as decltype is a C++ construct we can use it for all C++ enabled application, addressed in patch V2.
                    
>>Please use #elif instead of introducing a nested #if...#endif.
  Yes, taken care in patch V2.

Thanks,
Archana

On 3/19/20, 10:35 AM, "dev on behalf of Ben Pfaff" <ovs-dev-bounces at openvswitch.org on behalf of blp at ovn.org> wrote:

    On Thu, Mar 19, 2020 at 10:03:15AM -0700, Archana Holla via dev wrote:
    > OVS_TYPEOF macro doesn’t return the type of object for non __GNUC__ platforms.
    > Updating it for _WIN32 platforms when used from C++ code.
    > 
    > Signed-off-by: Archana Holla <harchana at vmware.com>
    > ---
    >  include/openvswitch/util.h | 4 ++++
    >  1 file changed, 4 insertions(+)
    > 
    > diff --git a/include/openvswitch/util.h b/include/openvswitch/util.h
    > index 9189e64..af7d1b0 100644
    > --- a/include/openvswitch/util.h
    > +++ b/include/openvswitch/util.h
    > @@ -86,8 +86,12 @@ OVS_NO_RETURN void ovs_assert_failure(const char *, const char *, const char *);
    >  #ifdef __GNUC__
    >  #define OVS_TYPEOF(OBJECT) typeof(OBJECT)
    >  #else
    > +#if defined (__cplusplus) && defined(_WIN32)
    > +#define OVS_TYPEOF(OBJECT) decltype(OBJECT)
    > +#else
    >  #define OVS_TYPEOF(OBJECT) void *
    >  #endif
    > +#endif
    
    Thanks for submitting a patch.
    
    Does this solve a problem?
    
    decltype is a C++ feature.  How is it specific to Windows?
    
    Please use #elif instead of introducing a nested #if...#endif.
    
    Thanks,
    
    Ben.
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