[ovs-dev] [PATCH v2] windows/lib: Fix Windows C++ compilation issues on common headers

[Shashank Ram]

On Thu, Nov 30, 2017 at 11:45 AM, Ben Pfaff <blp at ovn.org> wrote:

> On Wed, Nov 29, 2017 at 05:13:14PM -0800, Sairam Venugopal wrote:
> > Found when compiling the code with C++ binaries. Most of the issues are
> > due to missing explicit cast.
> >
> > Signed-off-by: Sairam Venugopal <vsairam at vmware.com>
> > Signed-off-by: Shireesh Kumar Singh <shireeshkum at vmware.com>
> > Co-authored-by: Shireesh Kumar Singh <shireeshkum at vmware.com>
>
> Hi Sairam, thanks for passing this along.
>
> The commit message does not explain the problem with
> PADDED_MEMBERS_CACHELINE_MARKER.  Can you help me to understand it?  The
> reason I would expect to add a new MSVC-only version is that it is
> impossible to write a single version (for C) that works with MSVC, GCC,
> and Clang, but I don't yet know a reason that is true.
>
> The header files in lib/ aren't exported for public consumption, which
> means that software other than Open vSwitch itself isn't expected to use
> them.  Of course, VMware and possibly others are actually doing that.  I
> have mixed feelings about that.  It's nice to know that OVS has useful
> header files, but I'm not so excited about the idea that every OVS
> header file has to work OK in C++.  Do you have any thoughts on how an
> OVS developer can guess whether a given header file will be used in C++?


Sai and Shireesh, thanks for the patch. I share the same sentiments as Ben
regarding
the usage of the header files in lib/. Since OVS is written in C, and this
patch attempts
to allow some headers in lib/ to be compiled using MSVC++, it might set a
precedent
where other headers might require to be changed as well just to be able to
compile
it in C++.  This is not very intuitive to an OVS developer about the
consumption
of the header file by a C++ compiler.
I feel it would be better to add a public header file for some of the
common headers
being consumed outside of OVS, and maybe even a version of the header file
that compiles fine in C++.