Re: [PATCH V4 1/8] libgpiod: Add libgpiod-sys rust crate

[Kent Gibson <warthog618@gmail.com>]

On Mon, Aug 01, 2022 at 05:41:06PM +0530, Viresh Kumar wrote:
> On 27-07-22, 13:17, Kent Gibson wrote:
> > On Wed, Jul 27, 2022 at 10:21:58AM +0530, Viresh Kumar wrote:
> > > On 27-07-22, 10:57, Kent Gibson wrote:
> > > > On Fri, Jul 08, 2022 at 05:04:54PM +0530, Viresh Kumar wrote:
> > > > > +fn main() {
> > > > > +    let files = vec![
> > > > > +        "../../../lib/chip.c",
> > > > > +        "../../../lib/chip-info.c",
> > > > > +        "../../../lib/edge-event.c",
> > > > > +        "../../../lib/info-event.c",
> > > > > +        "../../../lib/internal.c",
> > > > > +        "../../../lib/line-config.c",
> > > > > +        "../../../lib/line-info.c",
> > > > > +        "../../../lib/line-request.c",
> > > > > +        "../../../lib/misc.c",
> > > > > +        "../../../lib/request-config.c",
> > > > > +    ];
> > > > > +
> > > > > +    #[cfg(feature = "generate")]
> > > > > +    generate_bindings(&files);
> > > > > +    build_gpiod(files);
> > > > > +}
> > > > 
> > > > Shouldn't bindings wrap libgpiod and dynamically link against it rather
> > > > than building and linking statically?
> > > 
> > > There are few problems I faced, because of which I had to do it this way.
> > > 
> > > - I couldn't find a way to do a "Make" for libgpiod from here and then link to
> > >   the resultant library.
> > > 
> > > - libgpiod may not be automatically installed in the environment where the end
> > >   user of these Rust APIs exists. So I had to build it.
> > > 
> > > - And then the API is changing a lot, maybe down the line once it is stable
> > >   enough we can change this to something else.
> > > 
> > 
> > Sure, it is a problem, but static isn't the solution.
> > You should be able to get the appropriate paths from autoconf, but I would
> > refer you to Bart on that.
> 
> I am still looking for some help on how to link this dynamically.
> 
> FWIW, the problem is that the user crates, like vhost-device, will mention
> libgpiod as a dependency crate and likely won't have libgpiod installed in
> environment. So build.rs here needs to do some magic so the definitions are all
> available to the users.
> 

The Rust bindings themselves should be building against the local build
tree, so well known relative paths.

For users, require they have libgpiod installed and use pkg_config to
locate it?

Is that what you mean?

Else, how do other Rust crates wrapping dynamic C libraries do it?

Cheers,
Kent.