[LEDE-DEV] What's the purpose / gain from using VARIANT?

[Rafał Miłecki]

On 8 December 2016 at 02:00, Florian Fainelli <f.fainelli at gmail.com> wrote:
> On 12/07/2016 11:52 AM, Rafał Miłecki wrote:
>> On 12/07/2016 08:36 PM, Sergey Ryazanov wrote:
>>> On Wed, Dec 7, 2016 at 10:10 PM, Rafał Miłecki <zajec5 at gmail.com> wrote:
>>>> I'm aware some packages (e.g. upstream-ssl, hostapd, dnsmasq) use
>>>> VARIANT.
>>>>
>>>> I don't really understand the gain of this. How does it differ from
>>>> specifying separated packages?
>>>> I'm looking at package/libs/ustream-ssl/Makefile and I don't see much
>>>> code saving from using this VARIANT variable/feature.
>>>> Looking at package/system/opkg/Makefile I can see BUILD_VARIANT is
>>>> used for more specific CONFIGURE_ARGS. Is that where VARIANTS gets
>>>> really helpful?
>>>> Maybe I'm missing some real gain/value?
>>>
>>> IMHO VARIANT usage helps consolidate patches in single place. E.g. if
>>> you would like change some common code in hostapd then just create a
>>> new patch and VARIANT build two packages  (hostapd/wpa_supplicant)
>>> from updated code. Without VARIANT you should duplicate your changes
>>> (patch) in multiple places and keep them synchronized. So the gain is
>>> simple: reducing of unproductive work.
>>
>> I don't think sharing patches has anything to do with VARIANT. As long
>> as you
>> define packages in one Makefile they are going to share source (and so
>> patches).
>
> IMHO, this is more about sharing the build recipe more than anything
> else. Usually building from one variant to another is just a matter of
> tuning a bunch of build configuration parameters, but the bulk of how to
> build a package remains the same.

Thanks for your help, it makes more sense now.

My summary:
Packages defined in a single Makefile share PKG_* variables and
Build/* defines (steps). If packaged software doesn't generate
multiple files you want to put into separated packages AND you need to
adjust Build/* defines (steps) THEN having BUILD_VARIANT gets handy.

So VARIANT should be used when having:
1) Shared Build/Prepare
2) Shared Build/Compile
3) Separated Package/foo/install
isn't enough.

-- 
Rafał