Re: [PATCH 2/2] build: use dependency() instead of find_library()

On Thu, Jan 03, 2019 at 06:57:25PM +0100, Luca Boccassi wrote:

Whenever possible (if the library ships a pkg-config file) use meson's
dependency() function to look for it, as it will automatically add it
to the Requires.private list if needed, to allow for static builds to
succeed for reverse dependencies of DPDK. Otherwise the recursive
dependencies are not parsed, and users doing static builds have to
resolve them manually by themselves.
When using this API avoid additional checks that are superfluos and
take extra time, and avoid adding the linker flag manually which causes
it to be duplicated.

An internal checker has been added to Meson 0.42 to detect libpcap,
which ships a custom tool rather than a pkg-config file, so bump the
minimum Meson version from 0.41 to 0.42.

If we are going to bump the version, I think we should bump it further to
e.g. 0.46 or 0.47 unless there is anyone who still wants an earlier
version. That should get rid of a number of the meson version warnings we
see on each run.

For libbsd, which is checked in a top level file and used to be added
to the global linker flags array, add it to the ext_deps array of
all top level meson files (app, test, lib, examples, drivers). The
most correct change would be to let each individual library/driver/app
depend on it individually if they use symbols from it, but it would
diverge from the legacy Makefile's behaviour and make life a bit more
difficult for contributors.

It shouldn't be necessary to add libbsd as a dependency for everything. I
think just adding it as a dependency of EAL should work fine. However, in
conjunction with meson version checks, I believe this was done this way
originally because of a meson bug which caused recursive dependencies for
things like this to get duplicated many times in the build.ninja file.

https://github.com/mesonbuild/meson/issues/2150

If we take the approach of adding bsd explicitly using dependency object
our minimum version needs to have the fix for this bug included.

Fixes: a25a650be5f0 ("build: add infrastructure for meson and ninja builds")
Cc: stable@dpdk.org

Signed-off-by: Luca Boccassi <redacted>
---

Bruce, dependency() by default tries pkg-config first, then cmake, then
the internal project-specific finders (like pcap). If you think it's
worth it I can add fallbacks in case a system, for whatever reason,
does not install a pc file despite the upstream project providing one.
It would add more clutter and more verbosity, but it would not cause
other issues.

I'd prefer to keep it without that for now. If the lack of .pc files causes
issues we can revisit.

/Bruce