Re: [dpdk-dev] [PATCH] pci: fix missing pci bus with shared library build

[Stephen Hemminger <stephen@networkplumber.org>]

On Tue, 23 Jul 2019 09:59:04 +0200
Thomas Monjalon <thomas@monjalon.net> wrote:

> 22/07/2019 20:34, Stephen Hemminger:
> > On Mon, 22 Jul 2019 19:31:08 +0200
> > Thomas Monjalon <thomas@monjalon.net> wrote:
> >   
> > > 22/07/2019 19:13, Stephen Hemminger:  
> > > > Thomas Monjalon <thomas@monjalon.net> wrote:    
> > > > > Are the constructors run on dlopen of the bus driver?    
> > > > 
> > > > Yes, constructors are run on dlopen.
> > > > But application should not have to ask DPDK to dlopen the bus devices.
> > > > 
> > > > The core principle is that dynamic build of DPDK should act the same as old
> > > > statically linked DPDK. Otherwise, the user experience is even worse, and all
> > > > the example documentation is wrong.    
> > > 
> > > OK, this is where I wanted to bring the discussion.
> > > You are arguing against a design which is in DPDK from some early days.
> > > So this is an interesting discussion to have.
> > > Do we want to change the "plugin model" we have?
> > > Or do we want to simply drop this model (dlopen calls)
> > > and replace it with strong dynamic linking?  
> > 
> > I argue that examples should work the same with dynamic linking.
> > This used to work before the break out of the bus model, so it is a bug.  
> 
> The PCI support was part of EAL, yes, but the device drivers
> were plugins and already required the -d option.
> 
> > For distributions, this also matters. Linking with -ldpdk which is a linker
> > script should work.  
> 
> There is no longer this linker script with meson.
> 
> 

Ok, for usability that is a problem.
Requiring user to figure out which DPDK libraries to link with is a serious
waste of time. It should be possible to just link with -ldpdk and
distribution packages and just get the necessary libraries for the application
(no extra rte_foo_bar .so loaded at run time), and the application should
just work.

The idea that the user should link with 20 shared libraries, in the right
order and pass -d flags to eal_init to load the right PMD is user hostile.
It only makes sense if you want to invent yet another layer to manage the
ugly stuff hidden underneath. Think virt-manager versus raw KVM/QEMU.

I know it is hard, and I know not all this will make it into 19.08
but let's try and do better. The DPDK already has a reputation as being
like a super car, (ie unreliable and hard to drive). It doesn't have to be that way.