[libcamera-devel] [PATCH 4/5] android: Add camera metadata library
Jacopo Mondi
jacopo at jmondi.org
Tue Aug 6 12:38:04 CEST 2019
Hi Laurent,
On Mon, Aug 05, 2019 at 02:49:36PM +0300, Laurent Pinchart wrote:
> Hi Jacopo,
>
> Thank you for the patch.
>
> On Thu, Aug 01, 2019 at 05:54:19PM +0200, Jacopo Mondi wrote:
> > Import the Android camera metadata library from the ChromiumOS build
> > system.
> >
> > The camera metadata library has been copied from
> > https://chromium.googlesource.com/chromiumos/platform2
> > at revision ceb477360a8012ee38e80746258f4828aad6b4c7.
> >
> > The original path in the Cros platform2/ repository is:
> > camera/android/libcamera_metadata/src
> >
> > Create a new build target for the camera metadata library to
> > compile the libcamera Android HAL implementation against it.
> >
> > Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
> > ---
> > src/android/meson.build | 10 +
> > src/android/metadata/camera_metadata.c | 1204 +++++++
> > .../metadata/camera_metadata_tag_info.c | 2811 +++++++++++++++++
> > 3 files changed, 4025 insertions(+)
> > create mode 100644 src/android/meson.build
> > create mode 100644 src/android/metadata/camera_metadata.c
> > create mode 100644 src/android/metadata/camera_metadata_tag_info.c
> >
> > diff --git a/src/android/meson.build b/src/android/meson.build
> > new file mode 100644
> > index 000000000000..e988dfa9ee63
> > --- /dev/null
> > +++ b/src/android/meson.build
> > @@ -0,0 +1,10 @@
> > +android_camera_metadata_sources = files([
> > + 'metadata/camera_metadata.c',
> > +])
> > +
> > +# Do not install by default as the target systems (Android, ChromeOS) already
> > +# ship a libcamera_metadata.so library.
>
> Shouldn't you thus compile it statically (or at least as a static
> library) ? If we want to link at runtime against the shared library
> provided by the system then we should compile against the corresponding
> headers, not against our own copy of the headers. That wouldn't be
> practical, so statically linking is likely best.
>
Wouldn't this open door to mis-alignements between the metadata
library version we compile libcamera against and the one the camera
framework on the target system provides ? In the same way we might
have a mis-alignemnt of headers version when linking dynamically, we
would have the same if we statically link our version of the metadata
library.. This is tricky to solve, as we might then need to
ship/include different version of this library depending which is the
target system the HAL is compiled for... As of now, as we only target CrOS,
keeping in sync headers and the library from the cros sources and here
is not hard, but what when Android support will be added?
For now, with a single system supported, if we make sure headers and
the metadata library implementation are in sync between libcamera and
the cros sources, I guess statically linking would only give us a tad
fatter library without any additional guarantees.
> Longer term I think we should replace this with a custom C++
> implementation.
>
> > +android_camera_metadata = shared_library('camera_metadata',
> > + android_camera_metadata_sources,
> > + install : false,
> > + include_directories : android_includes)
> > diff --git a/src/android/metadata/camera_metadata.c b/src/android/metadata/camera_metadata.c
> > new file mode 100644
> > index 000000000000..6bfd02da29c7
> > --- /dev/null
> > +++ b/src/android/metadata/camera_metadata.c
> > @@ -0,0 +1,1204 @@
>
> SPDX here too please (in a separate patch).
>
> What are the implications of linking LGPL-2.1+ and Apache-2.0 code
> together ?
>
Eh, how fun is to deal with legal stuff..
So, not need to say but IANAL and none of us is, so the best source I
could find is this stackoverflow post
https://opensource.stackexchange.com/questions/5664/linking-from-lgpl-2-1-software-to-apache-2-0-library
The general question we are trying to answer is:
Can copyleft-licensed code depend on non-copyleft-licensed code that
is using a license that is deemed incompatible with a given copyleft
license?
Going through the answers and the FAQs on the GPL license website, it
seems the me the one that applies the most to our use case is:
What legal issues come up if I use GPL-incompatible libraries with
GPL software? If you want your program to link against a library
not covered by the system library exception, you need to provide
permission to do that.
So even though the LGPL is not the GPL, I would say that the best way
to do this would be to follow the guidelines provided at the FAQ and
license your LGPL library with an exception stating that this does not
extend to the Apache-licensed dependencies. Something similar to
OpenSSL exceptions commonly found in several places such as here.
That's because I'm not sure I found a proper definition of "system
library exception" for LGPL-2.1. If the metadata library falls under
that term, we should be good the way we are, otherwise we would need
to add a notice.
> > +/*
> > + * Copyright (C) 2012 The Android Open Source Project
> > + *
> > + * Licensed under the Apache License, Version 2.0 (the "License");
> > + * you may not use this file except in compliance with the License.
> > + * You may obtain a copy of the License at
> > + *
> > + * http://www.apache.org/licenses/LICENSE-2.0
> > + *
> > + * Unless required by applicable law or agreed to in writing, software
> > + * distributed under the License is distributed on an "AS IS" BASIS,
> > + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
> > + * See the License for the specific language governing permissions and
> > + * limitations under the License.
> > + */
>
> [snip]
>
> --
> Regards,
>
> Laurent Pinchart
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