[libcamera-devel] system locations of libcamera headers

[Kieran Bingham]

Hi Umang,

On 07/05/2021 06:24, Umang Jain wrote:
> Hi all,
> 
> If I compile the master branch with --prefix=/usr
> /meson --prefix=/usr -Dpipelines=uvcvideo,ipu3 build && sudo ninja -C
> build install/
> 
> 
> The headers turns out to have a directory structure as below:
> 
> 
> [uajain at localhost libcamera]$ tree /usr/include/libcamera/
> /usr/include/libcamera/
> ├── ipa
> │   ├── ipa_controls.h
> │   ├── ipa_interface.h
> │   └── ipa_module_info.h
> └── libcamera
>     ├── bound_method.h
>     ├── buffer.h
>     ├── camera.h
>     ├── camera_manager.h
>     ├── class.h
>     ├── compiler.h
>     ├── control_ids.h
>     ├── controls.h
>     ├── file_descriptor.h
>     ├── formats.h
>     ├── framebuffer_allocator.h
>     ├── geometry.h
>     ├── libcamera.h
>     ├── logging.h
>     ├── object.h
>     ├── pixel_format.h
>     ├── property_ids.h
>     ├── request.h
>     ├── signal.h
>     ├── span.h
>     ├── stream.h
>     ├── transform.h
>     └── version.h
> 
> 2 directories, 26 files
> 
> 
> My question is, is this how we want public headers to be placed ? For
> e.g. the absolute path of signal.h
> is/usr/include/libcamera/libcamera/signal.h, hence, even the below diff
> will compile successfully (due to linker find path magic)
> 
> diff --git a/src/libcamera/object.cpp b/src/libcamera/object.cpp
> index cd83c684..5f005d1b 100644
> --- a/src/libcamera/object.cpp
> +++ b/src/libcamera/object.cpp
> @@ -9,7 +9,7 @@
>  
>  #include <algorithm>
>  
> -#include <libcamera/signal.h>
> +#include <libcamera/libcamera/signal.h>


This gets 'found' because the include path is including "/usr/include/"
and your include statement specifies the double libcamera, which then
maps to the full /usr/include/libcamera/libcamera/signal.h path.

However, it's not correct to do so.

The path there is:

/usr/include/<project>/<component>/<header.h>

In this instance, both the project and the component have the same name.

> Considering the case where we also need to expose some of the internal
> libcamera headers on system locations (for IPAs to use) - It's better to
> kick off some dicussions around how we would structure the header
> locations. This will also clear some of my ongoing meson cleanup work
> (not all patches, but only a couple).

We already have /usr/include/libcamera/ipa/ for IPA interfaces to be
installed to.

The issue you are facing is that the IPA interfaces are referencing
'internal' and not installed or public headers from
<sourcetree>/include/libcamera/internal/<private files>

We need to identify which files are required by the IPA interfaces, and
find a way (or location) to install them, which makes them available to
the IPA interface, but makes it clear that they are /not/ a part of the
public API interfaces, and should not be accessible by applications.

Given that they are only to be used by the IPA, we could perhaps install
a subset of them into libcamera/ipa/internal/ or something like that.

I would like to be able to see a list of what files are required. That
would help in how we decide what files need abstracting or installing,
and where they should go.

--
Kieran


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-- 
Regards
--
Kieran