[dpdk-dev] NXP DPAA2: Symbol renaming issue: Request for Suggestions

[Shreyansh Jain]

Hello Ferruh,

On Tuesday 24 January 2017 09:54 PM, Ferruh Yigit wrote:
> On 1/24/2017 2:39 PM, Shreyansh Jain wrote:
>> Hello,
>>
>> We are facing a peculiar problem with respect to symbol namespace in DPDK. I
>> think Ferruh and Thomas would have fair idea about it as they have already
>> reviewed and commented on it. I was hoping to get some input to take it
>> forward from here.
>>
>> Brief Intro to DPAA2 Architecture:
>>
>> This is brief about NXP's DPAA2 PMD to start with:
>> (A lot more information is available at [1])
>>
>>
>>
>>                  +-------------------------------+
>>                  |         Application           |
>>                  +----.--------------------.-----+
>>                       |                    |
>>                  +----'------+       +-----'-----+
>>     drivers/---->|   DPIO    |       |   DPIO    |<---drivers/bus/fslmc
>>      bus/fslmc   +----.------+       +------.----+
>>                       |                     |
>>                  +----/-||--------------||--/----+
>>                  |   Queue/Buffer Manager        |<--- drivers/common/dpaa2
>>                  +----\-||--------------||--\----+      qbman
>>                       |                     |
>>                  +----'------+       +------'----+
>>     drivers/ --->|   DPNI    |       |   DPSEC   |<---drivers/cyrpto
>>      net/dpaa2   +----|------+       +-----|-----+     dpaa2_sec
>>                       |                    |
>>                  +----|------+      +------|-----+       +----------------+
>>                  | PHY H/W   |      |   SEC H/W  |      .> FSL MC BUS     |
>>                  +-----------+      +------------+     / +----------------+
>>                                                       drivers/bus/fslmc
>>
>>
>> If we consider the above layout, drivers/crypto/dpaa_sec (NXP's DPAA2 Crypto
>> PMD, already available on ML [2]), and drivers/net/dpaa2 (NXP's DPAA2 PMD) are
>> using a common code (drivers/common/dpaa2/qbman).
>>
>> QBMAN (drivers/common/dpaa2/qbman) is essentially a Queue and Buffer Manager
>> set of APIs which allow DPIO (Data Path IO interfaces) to communicate with the
>> Hardware through queues (and buffers).
>>
>> At the scan time, FSLMC bus is scanned and all devices (Phy or Sec) are
>> identified and added to a list. For each such device, appropriate I/O portals
>> are opened which are essentially gateway between user-space and DP* devices
>> using the hardware queues/buffers (qbman)
>>
>> Problem:
>>
>> You might have noticed that we have exposed a lot of symbols from
>> drivers/common and drivers/bus for drivers/net and drivers/crypto. All these
>> symbols are not rte_* as what has been suggested for exported symbols.
>>
>> Review comments have been received for renaming these to make them rte_* or
>> _rte_* prefixed.
>>
>> Just as a side note, these symbols are being exposed _internally_ within
>> drivers/* area.
>>
>> There are (3) possible solutions we have:
>
> What do you think about following:
>
> Create wrappers for DPDK with namespace, and export those for DPDK.
> And in the user side, create macros to convert them back.
>
> sample: [1]
>
> Although this may work, I am not sure this really worth the effort, if
> there is no intended consumer of these API other than dpaa2 code.
>
>
> [1]
> ======
>
> API .c (no modification):
> int func_foo() {};
> ------
>
> wrapper.c (new file):
> int rte_foo() {	return func_foo(); }
> ------
>
> *version.map:
> 	...
> 	rte_foo;
> 	...
> ------
>
> user dpdk_macro.h (new file):
> #define func_foo rte_foo
> ....
> ------
>
> user.c (no modification except include):
> #include "dpdk_macro.h"
>
> func_foo();
>
> ======
>

I too considered this option (1/ below). But, this is an unclean
approach. Adding wrappers around functions is going to performance 
impact considering that all the code in this library is datapath.

Besides, it means we need to maintain our APIs across internal changes
(though, API changes are not frequent, I agree).

Another option being what Thomas suggested - to keep the library
external to DPDK. That is better than this but would impact ease of use.
(And I do remember some comments on ML about external libraries not
being preferred.)

But, thanks for your suggestion. I need to figure out something.

>
>
>>
>> 1/ Rename all the symbols:
>>   - This is a difficult option for us. Renaming means breaking our linkage
>>     with existing code (Linux Kernel upstream candidate as well as internal
>>     repository).
>>   - Changing it means maintaining this change set internally/independently
>>     which is not a feasible long term solution.
>>
>> 2/ Merge all the libraries together:
>>   - In the initial RFC days, there were review comments which suggested that
>>     we should break the PMD into common libraries and place it in drivers/*
>>     parallel folders.
>>   - This is precisely the reason we are facing the situation.
>>   - Another possibility is to start duplicating the code for common. But, this
>>     too has a technical limitation for us as some data structures are shared
>>     across net and crypto and it is not possible to have multiple instances of
>>     those.
>>   - One more offshoot option could have been to keep the library external
>>     of the DPDK framework (external location and linked on demand basis,
>>     manually). We don't prefer this as this will make it difficult for any user
>>     to use DPAA2 easily.
>>
>> 3/ Finding a way to keep symbols internal to drivers/* independent of rte_*
>>    prefix:
>>    - For example, allowing symbols to be exposed limited to drivers/* area
>>      and not allowing them to be available across lib/* (not sure how, though!)
>>
>>    <This is where I need you help - is there some suggestion or comments which
>>     can help us arrive to a solution?>
>>
>>    My argument for this:
>>   - With new bus infra in place, there would be more drivers being contributed.
>>     It also means that there would be PMDs having their own code and symbol
>>     models. It would be difficult to ask all of them to mandatorily adhere
>>     to a naming scheme.
>>     This argument bodes well for lib/* because that is core (libraries) which
>>     should be controlled for uniformity and performance.
>>
>> [1] https://www.kernel.org/doc/readme/drivers-staging-fsl-mc-README.txt
>> [2] http://dpdk.org/ml/archives/dev/2017-January/054251.html
>>
>
>