RE: [PATCH v5 0/2] Add config file support for l3fwd

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> On Thu, Feb 24, 2022 at 02:46:24PM +0100, Thomas Monjalon wrote:
> > 24/02/2022 12:06, Ananyev, Konstantin:
> > > > > > > > > > > >> Or have a generic library for reading LPM entries.  L3fwd is supposed
> > > > > > > > > > > >> to be as small as possible (it no longer is), and the real work should
> > > > > > > > > > > >> be done by libraries to make it easier to build other applications.
> > > > > > > > > > > >
> > > > > > > > > > > > I never heard users ask about such thing,
> > > > > > > > > > > > but if there is a demand for that, then I suppose it could be considered.
> > > > > > > > > > > > CC-ing LPM/FIB maintainers to comment.
> > > > > > > > > > > > Though I believe it should be a subject of separate patch and discussion
> > > > > > > > > > > > (I think many questions will arise - what format should be, how to support
> > > > > > > > > > > > different types of user-data, to make it generic enough, etc.).
> > > > > > > > > > >
> > > > > > > > > > > Agree, it is very application specific, so it could be really difficult
> > > > > > > > > > > to make it generic.
> > > > > > > > > >
> > > > > > > > > > But several other also have LPM tables, so why not have common code for other applications.
> > > > > > > > > >
> > > > > > > > > > examples/l3fwd-power/main.c
> > > > > > > > > > examples/ipsec-secgw/rt.c
> > > > > > > > > > examples/ip_fragmentation/main.c
> > > > > > > > > > examples/l3fwd/l3fwd_lpm.c
> > > > > > > > > > examples/ip_reassembly/main.c
> > > > > > > > >
> > > > > > > > > Ah yes, that's good point.
> > > > > > > > > All these examples (except ipsec-secgw) started as l3fwd clones,
> > > > > > > > > so all of them have hard-coded LPM (and EM) tables too.
> > > > > > > > > Yes it would be good thing to address that problem too,
> > > > > > > > > and have some common code (and common routes file format) for all of them.
> > > > > > > > > I don't know is that a good idea to introduce parse file function in LPM/FIB library
> > > > > > > > > itself, might be better to  have something like examples/common/lpm_parse*.
> > > > > > > > > Anyway, this is an extra effort, and I think no-one has time for it in 22.03 timeframe.
> > > > > > > > > My suggestion would be for 22.03 go ahead with current l3fwd patches,
> > > > > > > > > then later we can consider to make it common and update other examples.
> > > > > > > >
> > > > > > > > I don't think this patch is urgent.
> > > > > > > > I suggest taking time to have common code for all examples
> > > > > > > > and target a merge in DPDK 22.07.
> > > > > > >
> > > > > > > Well, yes, from one perspective it not really a critical one,
> > > > > > > we do live with hard-coded routes inside l3fwd for nearly 10 year by now.
> > > > > > > Though l3fwd is one of mostly used examples inside DPDK and
> > > > > > > it is quite a pain to patch/rebuild it each time someone needs to run
> > > > > > > l3fwd with a different routing table.
> > > > > > > Merging this patch will allow people to use l3fwd for more realistic test
> > > > > > > scenarios in a painless manner.
> > > > > > > So I believe this patch is really helpful and should be beneficial for the whole community.
> > > > > > > Looking from that perspective, I don't see why it has to be "all or nothing" attitude here.
> > > > > > > Why we can't move one step at a time instead?
> > > > > > > That would allow to split and effort in terms of development/testing/upstreaming/etc.
> > > > > >
> > > > > > When a feature is merged, there is less incentives to rework.
> > > > > > That's why, when a feature is not urgent,
> > > > > > it is better to wait for the complete work.
> > > > >
> > > > > That's true till some extent, though from other side
> > > > > even without further rework that patch improves situation
> > > > > from what we have right now.
> > > > > So I don't see any harm here.
> > > >
> > > > It is adding a lot of code to an example which is already too big.
> > > > There are a lot of complain about the size of l3fwd.
> > > > That's why I think it makes sense to require this extra code
> > > > (not demonstrating anything, but just for testing convenience)
> > > > outside of the example.
> > >
> > > Ok, so your main concern is l3fwd code size increase, right?
> > > Then would it help if for we'll move file parsing code into a separate file(s)
> > > (under examples/l3fwd) for now?
> > > Something like examples/l3fwd/(lpm_em)_route_parse.c.
> >
> > Yes it would help to isolate the config file parsing code.
> > What others think?
> >
> I still would like config code for loading an LPM table or FIB table to be
> put inside the relevant libraries themselves, rather than having it in the
> examples themselves (even if shared between them).

Honestly, I don't see any good reasons for that:
I presume users of these libraries already have their own routing
config files with their own format requirements and I suppose
these formats differ a lot (depending on use-case).
For DPDK internal purposes (provide sample apps with ability to load routes dynamically)
some common code inside examples/ seems more than enough. 
Konstantin