[Gluster-devel] Modifying GlusterFS to cope with C99 inline semantics

[Anoop C S]

Hi all,

Due to the recent changes with GCC v5 [default standard is now GNU11],
we have been reported with some issues regarding undefined symbol
errors from different components. One important change while porting to
GCC v5 is with respect to inline functions [see GCC 5 porting changes @https://gcc.gnu.org/gcc-5/porting_to.html] These errors were basically root caused to the wrong usage of inline functions when compiled against GCC v5, which now follows the C99 inline semantics by default [previously it was GNU89 inline semantics]. Most of them were fixed at the earliest so that we don't see such errors in our normal work flow. Latest one was failure to start the volume when glusterfs was compiled in debug mode. This was not seen when compiled in non-debug mode due to the presence of a particular compiler optimization level provided via configure.ac [see detailed discussion @ http://www.gluster.org/pipermail/gluster-devel/2015-July/046211.html].

Inline functions which doesn't require external usage.
------------------------------------------------------
Looking through the code base, we can see considerable instances for
inline functions. According to C99 inline rules [
http://www.greenend.org.uk/rjk/tech/inline.html], if we wanted to keep
our inline function entirely private to one translation unit, we make
it static inline. As of now there are instances where we have failed to
do so. It is recommended to have those functions as static inline if we
really require those functions to be 'inlined' and can be easily done.
Or else we can just remove the inline keyword as a whole.

Inline functions which require external usage.
----------------------------------------------
On the other side, we have inline functions defined to be used
externally. The current implementation in glusterfs doesn't follow the
proper inline semantics for such functions. An inline function must be
defined in all files that calls it. According to C99 rules [
http://www.greenend.org.uk/rjk/tech/inline.html], there are two ways to
generate such an external definition for inline functions. Apart from
defining the inline function in a .h file we need to either declare it
as 'extern' exactly once or declare it by omitting 'inline' exactly
once.

In doing so we can make sure that the compiler sees the definition
whenever it is used from multiple files and can be 'inlined'
effectively. For us, this correction will require moving definitions
out of .c files to .h file. Instead of changing all such instances by a
single person, it can be done component-wise. Here also we have the
other option of removing the inline keyword as a whole.

Overall, we have 3 options:
[1] Fix all inline functions according to C99 standard.
[2] Fix only those inline functions which doesn't require external
linkage and remove inline from those who require external linkage.
[3] Remove the inline keyword from functions. 

Suggestions/comments are mostly welcome.

Thanks,
--Anoop C S.