Hi,
On 12.08.2014 02:21, Ivan Kalvachev wrote:
On 8/11/14, Andreas Cadhalpun <andreas.cadhal...@googlemail.com> wrote:
Assuming it would be possible to install development packages for both
at the same time, which one should be used, when building a program?
It would be decided by the gcc -I inclusion option.
But this path has to come from the pkg-config files.
It modifies the search paths for header files, so that it checks these
paths before the system/default ones (When using `#include
"libavcodec/avcodec.h" `)
Libav headers are probably going to remain in the default /usr/include/ .
Usually this should not be a problem, unless a program uses `#include
<libavcodec/avcodec.h> ` that should be used for system headers (aka
checks the system/default paths first).
But a lot of programs use '#include <libavcodec/avcodec.h>'.
There might still be problems if there are explicit -I/usr/include
inserted by other libraries that mix the inclusion order.
To avoid hard to debug compiling problems, that the -dev packages may
still be marked as conflicting, even though no files are overwritten.
This final conflict however cannot be resolved on FFmpeg side.
Yes, they still have to conflict.
The change is reflected in the pkgconfig files too. Since applications
that link to libraries with addition suffixes should be using
pkgconfig, they would be using the correct header includes
automatically.
If that's to be determined via pkg-config files, then the obvious
problem is that both install these files in the same location, and if
one doesn't, programs can't find the library.
The problem is not that they are installed in the same location, but
that they have same names.
However I just checked and when you define library suffix (e.g.
--build-suffix="_ffmpeg"), it also adds the same suffix to the .pc
files. So you have
/usr/lib/share/pkgconfig/libavcodec_ffmpeg.pc
/usr/lib/libavcodec_ffmpeg.so
Yes, but I patched that out in the Debian package [1], because otherwise
the programs wouldn't find the pkg-config files.
In short, assuming if Libav doesn't change their library names and
pkgconfig files,
the programs that are looking for 'libavcodec.pc' would get the Libav one,
the programs that are looking for 'libavcodec_ffmpeg.pc' would get FFmpeg.
The problem is that programs only look for libavcodec.pc.
I believe that you should already be using --build-suffix, so that
should already be in the package.
Is there something else I'm missing?
Probably, that the pkg-config files in the FFmpeg package for Debian are
still libavcodec.pc etc..
I did just a rudimentary test and I couldn't spot anything wrong.
Please test it before inclusion.
The patch seems to be alright, but it doesn't make it possible to make
the development packages of FFmpeg and Libav co-installable.
Unfortunately not.
But without the patch the problem is entirely in how FFmpeg installs its header.
With it, it is entirely Libav problem for using system/common
directory. Then, if Debian wants to resolve the conflict, Libav header
files could be moved in their own directory. The patch should be
trivial to port.
I still don't see what the benefit would be, as the *-dev packages still
have to conflict.
As for the future, it might be good idea next major release (e.g. 3.0)
to have the $prefix/include/ffmpeg as default include path (for
non-comapt build).
So this would also not help.
At the moment FFmpeg is trying to mimic 100% Libav API/ABI, and to be
perfect drop-in replacement. This means using the same library names,
locations and header files.
This is what I call compat build. It is 100% compatible with Libav
from application/program point of view.
When using --build-suffix, you obviously want to differentiate from
Libav, so I call that non-compat build.
Except that the programs still should be able to build, ideally with
both, and which one is used during build is defined by which *-dev
packages are installed. This is the reason, why the pkg-config file
names have to be the same.
Sorry if this is caused confusion.
I hope that the way Debian packages FFmpeg would actually turn out to
be the new default.
Best regards,
Andreas
1:
https://anonscm.debian.org/cgit/collab-maint/ffmpeg.git/tree/debian/patches/pkg-config_file_without_build_suffix.patch
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