Re: [PATCH 1/1] eal: add C++ include guard in generic/rte_vect.h

[Bruce Richardson <bruce.richardson@intel.com>]

On Fri, Feb 02, 2024 at 10:18:23AM +0100, Thomas Monjalon wrote:
> 02/02/2024 06:13, Ashish Sadanandan:
> > The header was missing the extern "C" directive which causes name
> > mangling of functions by C++ compilers, leading to linker errors
> > complaining of undefined references to these functions.
> > 
> > Fixes: 86c743cf9140 ("eal: define generic vector types")
> > Cc: nelio.laranjeiro@6wind.com
> > Cc: stable@dpdk.org
> > 
> > Signed-off-by: Ashish Sadanandan <ashish.sadanandan@gmail.com>
> 
> Thank you for improving C++ compatibility.
> 
> I'm not sure what is best to fix it.
> You are adding extern "C" in a file which is not directly included
> by the user app. The same was done for rte_rwlock.h.
> The other way is to make sure this include is in an extern "C" block
> in lib/eal/*/include/rte_vect.h (instead of being before the block).
> 
> I would like we use the same approach for all files.
> Opinions?
> 
I think just having the extern "C" guard in all files is the safest choice,
because it's immediately obvious in each and every file that it is correct.
Taking the other option, to check any indirect include file you need to go
finding what other files include it and check there that a) they have
include guards and b) the include for the indirect header is contained
within it.

Adopting the policy of putting the guard in each and every header is also a
lot easier to do basic automated sanity checks on. If the file ends in .h,
we just use grep to quickly verify it's not missing the guards. [Naturally,
we can do more complete checks than that if we want, but 99% percent of
misses can be picked up by a grep for the 'extern "C"' bit]

/Bruce