Re: [dpdk-dev] [PATCH v2 0/4] add static ibverbs in meson

[Bruce Richardson <bruce.richardson@intel.com>]

On Tue, Feb 04, 2020 at 04:14:46PM +0100, Thomas Monjalon wrote:
> 04/02/2020 15:33, Bruce Richardson:
> > On Tue, Feb 04, 2020 at 03:27:50PM +0100, Thomas Monjalon wrote:
> > > 04/02/2020 12:48, Bruce Richardson:
> > > > as we discussed offline, I really don't like the necessity of the
> > > > hidden_deps part of this, so I've tried coming up with some other
> > > > solutions.
> > > 
> > > Thanks for looking closely at these patches.
> > > 
> > > > For example, in my testing I get the same result with the
> > > > following diff instead of the second two patches (just showing for mlx5 -
> > > > changes for mlx4 are identical):
> > > [...]
> > > > -                       # Build without adding shared libs to Requires.private
> > > > -                       hidden_deps += lib.partial_dependency(compile_args:true)
> > > [...]
> > > > +       ibv_cflags = run_command(find_program('pkg-config'), '--cflags', 'libibverbs').stdout()
> > > [...]
> > > > By doing things this way - assuming it works in your tests too - we avoid
> > > > any need to change anything in the common drivers code.
> > > 
> > > Yes, you hide the dependency by getting cflags directly with pkg-config.
> > > I wanted to avoid such solution because I was trying to use as much
> > > as possible the meson infrastructure.
> > > 
> > > I think your solution relying on one more call to pkg-config is acceptable.
> > > I will test it and will review whether we get all corner cases.
> > > 
> > 
> > Thanks.
> > It's not really ideal, but this is likely always going to be a bit flakey
> > since we can't use distro-supplied .a files, and your scripting is needed
> > to prevent even accidentally taking a non-custom-build rdma-core file.
> > Furthermore, I see that while meson tracks PKG_CONFIG_PATH value itself for
> > finding things, this does not get tracked between runs for shell calls.
> > This can catch one out, for example:
> > 
> > PKG_CONFIG_PATH=/path/to/pc/files meson build
> > 
> > will work correctly for everything. However, if one does a reconfigure
> > subsequently doing e.g. ninja reconfigure, meson will correctly pick up the
> > .pc files, but the ibverbs-static script, or any run_command calls to
> > pkg-config won't as it's not actually in the environment :-(
> 
> In my setup, I export PKG_CONFIG_PATH, so it is not an issue.
> But I understand your point that we may hit the issue.
> That's why I will work in meson upstream to avoid all of this in future.
> 
+1

> 
> > > In the meantime I discovered we are overlinking with meson
> > > when using the dlopen linking option.
> > > I will try to fix it as well with the same method.
> > > 
> > Right. Overlinking is probably less serious an issue though. Does it cause
> > any real-world problems?
> 
> Overlinking defeats the benefit of dlopen.
> The idea of dlopen is to avoid having ibverbs as mandatory DPDK dependency.
> The ibverbs lib is loaded with dlopen only if probing a Mellanox device.
> The dlopen solution makes the PMD really like an optional plugin,
> same as for static linkage in the PMD.
> 
Right, I understand the issue now.