[libcamera-devel] [PATCH] py: libcamera: Improve python binding installation

[Tomi Valkeinen]

On 26/10/2023 13:15, William Vinnicombe wrote:
> Hi both,
> 
> Thanks for your comments - I hadn't considered cross compilation, but 
> from looking into it I can see that this change would cause the problems 
> you've mentioned. Would it be an acceptable solution to wrap these 
> changes within "if meson.is_cross_build() else ..." so that cross 
> compilation uses the previous code still, but native compilation uses 
> the meson python module? If so, I'll submit a v2 with those changes.

I don't see why not, presuming it works =). Do you have a 
cross-compilation environment (e.g. buildroot) for testing?

  Tomi

> 
> Thanks,
> 
> William
> 
> On Thu, 26 Oct 2023 at 06:39, Tomi Valkeinen 
> <tomi.valkeinen at ideasonboard.com 
> <mailto:tomi.valkeinen at ideasonboard.com>> wrote:
> 
>     On 25/10/2023 14:04, Laurent Pinchart wrote:
>      > Hi William,
>      >
>      > (CC'ing Tomi)
>      >
>      > Thank you for the patch.
>      >
>      > On Wed, Oct 25, 2023 at 10:36:49AM +0100, William Vinnicombe via
>     libcamera-devel wrote:
>      >> The existing meson.build file installs the bindings to an
>     architecture
>      >> specific libdir (eg /usr/local/lib/aarch64-linux-gnu/), which is not
>      >> picked up by default python which only looks in the non architecture
>      >> specific libdir (eg /usr/local/lib/python3.11/). It also will always
>      >> build using the system python, rather than building using the same
>      >> python as meson is using. This prevents a user being able to
>     build the
>      >> bindings for a different version of python, without changing their
>      >> system python to that version.
>      >>
>      >> Modify the build process to use the meson Python module to build the
>      >> python bindings targets, so it installs them to the correct
>     directories
>      >> for python, and builds them for the version of python that meson is
>      >> running with.
>      >>
>      >> Signed-off-by: William Vinnicombe
>     <william.vinnicombe at raspberrypi.com
>     <mailto:william.vinnicombe at raspberrypi.com>>
>      >> ---
>      >>   src/py/libcamera/meson.build | 23 ++++++++++++-----------
>      >>   1 file changed, 12 insertions(+), 11 deletions(-)
>      >>
>      >> diff --git a/src/py/libcamera/meson.build
>     b/src/py/libcamera/meson.build
>      >> index f58c7198..e9e3f915 100644
>      >> --- a/src/py/libcamera/meson.build
>      >> +++ b/src/py/libcamera/meson.build
>      >> @@ -1,6 +1,8 @@
>      >>   # SPDX-License-Identifier: CC0-1.0
>      >>
>      >> -py3_dep = dependency('python3', required : get_option('pycamera'))
>      >> +
>      >> +py = import('python').find_installation('python3', required :
>     get_option('pycamera'))
>      >> +py3_dep = py.dependency(required : get_option('pycamera'))
>      >
>      > Does this still work when cross-compiling ? I recall we tried the
>     meson
>      > python module, and it had problems with cross-compilation. Tomi
>     may know
>      > more.
> 
>     Right. When cross-compiling, you don't want that "[the build process]
>     builds them for the version of python that meson is running with", as
>     meson is running (for me) in x86 environment, but the target is arm.
> 
>     I'm not sure if there's been any work on fixing all that in the meson
>     side, but the last time I talked to them they didn't have any clear
>     ideas how to fix it.
> 
>     Perhaps this can be solved by manually dealing with all the python
>     details in the meson.build file, and adding a meson option so that the
>     user can tell which python to use.
> 
>        Tomi
>