[dpdk-dev] [RFC PATCH 0/5] rework feature enabling macros for compatibility

[Ferruh Yigit]

On 9/18/2020 9:59 AM, Andrew Rybchenko wrote:
> On 9/18/20 11:41 AM, Bruce Richardson wrote:
>> On Thu, Sep 17, 2020 at 08:59:26PM +0300, Andrew Rybchenko wrote:
>>> On 9/16/20 7:44 PM, Bruce Richardson wrote:
>>>> As flagged previously on-list, there are a number of macros used to specify
>>>> what libs and drivers are enabled in the build which differ from the
>>>> equivalents used with make. This patchset is one possible approach to
>>>> fixing these, but as part of the investigation some issues were hit where
>>>> I'd like additional input to ensure we are ok with the approach taken in
>>>> this set.
>>>>
>>>> First, a problem statement:
>>>>
>>>> * While the make build defines generally followed a pattern, there were
>>>>     many instances where the defines were unique. These can be seen in the
>>>>     values defined in patch 4.
>>>>
>>>> * The NIC PMDs had two separate standards for the defines - some (the
>>>>     physical device drivers) tended to have the _PMD at the end of the
>>>>     macros, while the virtual drivers had it in the middle. Since the
>>>>     majority seemed to go with it at the end, meson chose this option.
>>>>     However, as can be seen from patch 4, a number now need special handling
>>>>     for compatibility
>>>>
>>>> * This "_PMD" at the end made its way into other device classes, such as
>>>>     crypto and event, but it appears that the standard for these classes from
>>>>     make is in fact the opposite. Therefore we have had for the last 2+ years
>>>>     conflicting macros for crypto, compression and event classes.
>>>>
>>>> * There is also the question of how important compatibility for these
>>>>     macros is, especially since we have had numerous incompatibilities
>>>>     without it being reported before. There is also the issue of the
>>>>     deprecation process for macros, since these are not part of any ABI.
>>>>
>>>> What's done in this set:
>>>>
>>>> * Firstly, and missing dependencies on apps or examples had to be fixed,
>>>>     where a dependency was missed because it was never needed due to the code
>>>>     being stripped out because of a missing macro.
>>>>
>>>> * Secondly, since it is likely that use of the defines from make is more
>>>>     widespread than those from meson, the defines for the crypto, compression
>>>>     and event classes are changed to align with the make values. Just in case
>>>>     though, temporary code is added to drivers/meson.build to redefine the
>>>>     old meson values too, and a deprecation notice is added for these. The
>>>>     hope is that we can then remove this temporary code in the next release,
>>>>     leaving us with just one macro style for each driver class.
>>>>
>>>> * Thirdly, we add an additional set of backward compatibility macros for
>>>>     the ~30 special-cases, where the meson macro template does not match that
>>>>     defined for make. Again, this is intended to be temporary and a
>>>>     deprecation notice is given for the macros in that file.
>>>>
>>>> * Finally, we replace all instances of the old macros in the codebase with
>>>>     the newer versions. While the work done in the first four patches (steps
>>>>     1-3 above) should be ok to backport, this final patch is not suitable for
>>>>     backporting. However, it is relatively simple to produce a new patch for
>>>>     backporting which allow either old or new values to be used in macros.
>>>>
>>>>
>>>> Open issues/considerations after this patch:
>>>>
>>>> * We still have inconsistencies in our driver macro and naming templates.
>>>>     This is just a nice-to-have, but if people are ok with generally having a
>>>>     breakage in our macro defines, we could clean this up a lot further.
>>>>     Notice how 'net', 'regex' and 'vdpa' have '_PMD' at the end, while most
>>>>     others have it before the name. Notice also that many device classes have
>>>>     the class at the end of the template, while bbdev has it in the middle.
>>>> 	$ git grep config_flag_fmt -- drivers/*/meson.build
>>>> 	drivers/baseband/meson.build:config_flag_fmt = 'RTE_LIBRTE_PMD_BBDEV_ at 0@'
>>>> 	drivers/bus/meson.build:config_flag_fmt = 'RTE_LIBRTE_ at 0@_BUS'
>>>> 	drivers/common/meson.build:config_flag_fmt = 'RTE_LIBRTE_ at 0@_COMMON'
>>>> 	drivers/compress/meson.build:config_flag_fmt = 'RTE_LIBRTE_PMD_ at 0@'
>>>> 	drivers/crypto/meson.build:config_flag_fmt = 'RTE_LIBRTE_PMD_ at 0@'
>>>> 	drivers/event/meson.build:config_flag_fmt = 'RTE_LIBRTE_PMD_ at 0@_EVENTDEV'
>>>> 	drivers/mempool/meson.build:config_flag_fmt = 'RTE_LIBRTE_ at 0@_MEMPOOL'
>>>> 	drivers/net/meson.build:config_flag_fmt = 'RTE_LIBRTE_ at 0@_PMD'
>>>> 	drivers/raw/meson.build:config_flag_fmt = 'RTE_LIBRTE_PMD_ at 0@_RAWDEV'
>>>> 	drivers/regex/meson.build:config_flag_fmt = 'RTE_LIBRTE_ at 0@_PMD'
>>>> 	drivers/vdpa/meson.build:config_flag_fmt = 'RTE_LIBRTE_ at 0@_PMD'
>>>
>>> As a generic direction I would vote for standard names which are
>>> based on directory structure:
>>>   - RTE_LIBRTE_ETHDEV
>>>   - RTE_DRIVER_NET_SFC
>>>   - RTE_DRIVER_COMMON_MLX5
>>>   - RTE_DRIVER_BUS_PCI
>>>
>>
>> Definite +1, and it would be good if we standardized the .so names like
>> that too.
>>
>> The open question is how much backward compatibility needs to be maintained
>> for macros (and also too for .so names)? With this patchset, I've aimed
>> very much to keep strict compatibility for now.
> 
> I think it is really good. Technically it does not look hard to
> provide backward compatibility for macros, so I'd keep it up to
> but not including 21.11 (next LTS?). Same for .so names, if it
> is not a problem.
> 
> If we approve the decision on naming, all new entities must
> follow it from the very beginning.
> 

+1