Re: [dpdk-dev] [PATCH 1/1] build: allow disabling libs

[Mohammed Hawari <mohammed@hawari.fr>]

Hello Bruce,

Thanks for the quick response, see inline

Best regards,

Mohammed

> On 18 Sep 2020, at 13:43, Bruce Richardson <bruce.richardson@intel.com> wrote:
> 
> On Fri, Sep 18, 2020 at 10:49:23AM +0200, Mohammed Hawari wrote:
>> Similarly to the disable_drivers option, the disable_libs option is
>> introduced. This allows to selectively disable the build of elements
>> in libs to speed-up the build process.
>> 
>> Signed-off-by: Mohammed Hawari <mohammed@hawari.fr>
>> ---
> 
> While I don't particularly like allowing libs to be enabled and disabled
> since it complicates the build, I can see why it's necessary. This is an
> area that does need some discussion, as I believe others have some opinions
> in this area too.
> 
> However, for now, some additional thoughts, both on this patch and in
> general:
> 
> 1. I see you included disabling apps if their required libs are not
>   available. What about the drivers though?
To my understanding, in the current code, the drivers/meson.build file already
does that check with:

foreach d:deps
                if not is_variable('shared_rte_' + d)
                    build = false

> 2. A bigger issue is whether this is really what we want to do, guarantee a
>   passing build even if vast chunks of DPDK are actually enabled? I'd tend
>   towards "no" in this case, and I'd rather see disabling of libs more
>   constrained.
> 3. To this end, I think I'd rather see us maintain a set of libs which are
>   allowed to be disabled, and prevent the rest from being so. For example,
>   it makes no sense in DPDK to disable the EAL or mempool libs, since nothing
>   will build, while the bitrate_stats or latency_stats libs could likely
>   be disabled with little or no impact.
I tend to agree with that more structured approach, but I am going to wait until
we get some more thoughts from the community before starting that work.

> Therefore, I think a better implementation is to start as in this patch
> with a new config parameter to disable libs, but as part of that patch add
> in an internal list of the libs which are allowed to be disabled (initially
> empty). Telling the build system to disable a lib not on that list should
> raise a configuration time error. As for how a lib gets on the list - that
> should be done once the build has been tested with that lib disabled, i.e.
> once testpmd and other apps have got #defines in the code for stripping out
> the disabled blocks, and any drivers which depend on the lib have proper
> checks and warnings in place about it being disabled (or also #defines in
> the code if that can be done).
> 
> The other advantage of maintaining such a list is that it then becomes
> somewhat feasible to test these build settings, in that (maybe once per
> release), iterate through the list of disable-able libs and test that the
> build passed with each one disabled individually. [I think for this purpose
> we can ignore interactions of having two disabled simultaneously, in order
> to have something testable]
> 
> What do others in the community think?
> 
> Regards,
> /Bruce