Re: [dpdk-dev] [PATCH RFC] Update/Improve build system

["Gonzalez Monroy, Sergio" <sergio.gonzalez.monroy@intel.com>]

Hi,

Apologies for the previous email format, I seems like I misconfigured something on my email-client.
In case people find it annoying to read with extra line spaces, here is the RFC with fixed formatting:


I would like to propose an update on the way the libraries are being built on DPDK.

Motivation/Issues:
- No agreement on libraries to build (separated, combined, different grouping).
- People having issues building their applications cannot rely on the information given by ldd when using shared libraries because currently we are not building against dependent libraries.
- External library dependencies are introduce in multiple places (ie. when building librte_vhost, -lfuse is added into the lib CFLAGS, LDFLAGS and also need to update rte.app.mk).
- Do we want to keep support for building shared libraries using LD? Currently unused as both Linux and BSD enable linking using CC.

Proposal:
- Define external lib dependencies per module/lib/dir. ie. EXT_DEP_LIBS = -lfuse -lm
- Define internal lib dependencies per module/lib/dir. ie. DPDK_DEP_LIBS = -lrte_eal
- Remove compile config option CONFIG_RTE_BUILD_COMBINE_LIBS and always build all wanted libraries (see below about different libraries to build).
- Shared linking: we want to link apps and libs against dependant libraries. Basically add EXT_DEP_LIBS and DPDK_DEP_LIBS when linking libs and apps.
- Static linking: we want to link apps against dependant libraries.

>From my point of view, we can classify DPDK libraries into three categories (note that not all libraries are included and the following is just for illustration purposes):
CORE_LIBS: librte_kvargs, librte_mbuf, librte_malloc, librte_mempool, librte_ring, librte_eal, libethdev?
NON_CORE_LIBS: librte_vhost, librte_cfgfile, librte_cmdline, librte_sched, librte_lpm, librte_acl, ...
PMD_LIBS: librte_pmd_i40e, librte_pmd_e1000, librte_ixgbe, ...

IMHO CORE_LIBS are a set of libraries that have inter-dependencies and are always required to build an application. Such set of core libraries should be provided as a single library.
I can think of a few different ways to go about this:
A) Build just one combined library for static or shared libraries.
     Pros: it would reduce and simplify makefile rules, as well as make it easier for users to build their own apps against DPDK.
     Cons: limited flexibility when building custom apps with selected libraries.     Link apps with something like:
                --whole-archive -ldpdk --no-whole-archive --as-needed $(EXT_DEP_LIBS) --no-as-needed
B) Build CORE_LIBS (as a single lib, librte_core), NON_CORE_LIBS and PMD_LIBS:
     Pros: flexibility.
     Cons: more complex build process, as we would add dependencies for each NON_CORE_LIB and PMD_LIB.     Link apps with something like:
                --whole-archive $(PMD_LIBS) --no-whole-archive $(NON_CORE_LIBS) -lrte_core --as-needed $(EXT_DEP_LIBS) --no-as-needed
C) Similar to B but building a single library containing both CORE_LIBS and NON_CORE_LIBS.
     Link apps with something like:
                --whole-archive $(PMD_LIBS) --no-whole-archive -lrte_xxxx --as-needed $(EXT_DEP_LIBS) --no-as-needed
D) Build all libs in both A) and B) but linking DPDK provided apps only against combined lib for slightly simpler makefile rules.

I would say that D) is a good balance, although not being the simplest.

Thoughts?

Thanks,
Sergio