[dpdk-dev] [PATCHv4 0/4] dpdk: enhance EXPERIMENTAL api tagging

[Neil Horman <nhorman@tuxdriver.com>]

Hey all-
        A few days ago, I was lamenting the fact that, when reviewing patches I
would frequently complain about ABI changes that were actually considered safe
because they were part of the EXPERIMENTAL api set.  John M. asked me then what
I might do to improve the situation, and the following patch set is a proposal
that I've come up with.

        In thinking about the problem I identified two issues that I think we
can improve on in this area:

1) Make experimental api calls more visible in the source code.  That is to say,
when reviewing patches, it would be nice to have some sort of visual reference
that indicates that the changes being made are part of an experimental API and
therefore ABI concerns need not be addressed

2) Make experimenal api usage more visible to consumers of the DPDK, so that
they can make a more informed decision about the API's they consume in their
application.  We make an effort to document all the experimental API's, but
there is no guarantee that a user will check the documentation before making use
of a new library.

This patch set attempts to achieve both of the above goals.  To do this I've
added an __experimental macro tag, suitable for inserting into api forward
declarations and definitions.

The presence of the tag in the header and c files where the api code resides
increases the likelyhood that any patch submitted against them will include the
tag in the context, making it clear to reviewers that ABI stability isn't a
concern here.

Also, This tag marks each function it is used on with an attibute causing any
use of the fuction to emit a warning during the build
with a message indicating that the API call in question is not yet part of the
stable interface.  Developers can then make an informed decision to suppress
that warning or not.

Because there is internal use of several experimental API's, this set also
includes a new override macro ALLOW_EXPERIMENTAL_APIS to automatically
suprress these warnings.  I think its fair to assume that, for internal use, we
almost always want to suppress these warnings, as by definition any change to
the apis (even their removal) must be done in parallel with an appropriate
change in the calling locations, lest the dpdk build itself break.

Neil

---
Change Notes:
v2)
* Cleaned up checkpatch errors
* Added Allowance for building experimental on BSD
* Swapped Patch 3 and 4 so that we didn't have a commit level that issued
  warnings/errors without need

v3)
* On suggestion from Bruce, modify ALLOW_EXPERIMENTAL_APIS to be defined in
  CFLAGS rather than a makefile variable.  This is more flexible in that it
  allows us to suppress this specific feature rather than all uses of the
  deprecated attribute, as we might use it for other features in the furute

v4)
* Added documentation patch to contributors guide