[PATCH 5/5] build: select optional libraries

[Thomas Monjalon]

10/11/2021 18:34, Bruce Richardson:
> On Wed, Nov 10, 2021 at 05:48:14PM +0100, David Marchand wrote:
> > There is currently no way to know which libraries are optional.
> > Introduce a enable_libs option (close to what we have for drivers) so
> > that packagers or projects consuming DPDK can more easily select the
> > optional libraries that matter to them and disable other optional
> > libraries.
> > 
> > Note: the enabled_libs variable is renamed for sake of consistency.
> > 
> > Signed-off-by: David Marchand <david.marchand at redhat.com>
> > ---
> This is the only patch of this set I would have some concerns about. I'm
> just not sure that it makes sense to have this option for libraries
> compared to drivers.
> 
> Specifically:
> * We have over 200 drivers in DPDK (rough count using find), of which 2 are
>   mandatory, and therefore specifying just 1 or 2 that you want can make
>   sense.
> * On the other hand, we have 53 libraries, of which only 7 or so (after
>   this patchset) are optional. This means that use of the term
>   "enable_libs" is misleading - at least to me - in that it's only a very
>   small proportion of the libs which would be affected by that flag
>   (compared to 99% of the drivers)

The options are described like this:

option('disable_libs', type: 'string', value: '', description:
       'Comma-separated list of libraries to explicitly disable. [NOTE: not all libs can be disabled]')
+option('enable_libs', type: 'string', value: '', description:
+       'Comma-separated list of libraries to explicitly enable.')

I feel we should mention it is enabling optional libraries,
and the default is to enable all.

> * Also, while the number of mandatory drivers is unlikely to change much
>   (since there are only 2), it should be fairly safe to do builds using
>   "--enable-drivers". On the other hand, the list of libraries affected by
>   "--enable-libs" is likely to change, so short of each user naming each
>   and every lib they use (and each library those depend on), to the list,
>   it's quite possible that any --enable-libs use could lead to a broken
>   build in future if a library changes from mandatory to optional.

In order to be safe, the user can list all required libs,
including non-optional ones.

> Overall, I'm just concerned that this flag is premature, and would prefer
> to keep it just to the disable option until we are confident that out
> "optional library" list is relatively settled.

I see it the opposite way:
Someone who does not wish to deliver extra libs could use this option
to list the required libs, so not-required libs will disappear from
the build once they are declared optional in future releases.