[Buildroot] [RFC v1] libv4l: build utils only on MMU (with fork support) platforms
hugues.fruchet at st.com
Tue Jul 18 09:08:18 UTC 2017
On 07/17/2017 08:09 PM, Peter Seiderer wrote:
> Hello Hugues,
> On Mon, 17 Jul 2017 10:07:07 +0000, Hugues FRUCHET <hugues.fruchet at st.com> wrote:
>> Hi Peter,
>> I have tested on STM32 platform running Cortex F family having no MMU,
>> shared libraries are disabled (no dlopen) and no fork supported on our
>> libv4lconvert should not have been built at all, because entire lib/
>> folder build is conditional to shared library support:
>> * configure.ac
>> AM_CONDITIONAL([WITH_LIBV4L], [test x$enable_libv4l != xno -a
>> x$enable_shared != xno])
>> * Makefile.am
>> +if WITH_LIBV4L
>> +SUBDIRS += lib
> A little bit confused, one of the patches you introduced changed it to:
> - without WITH_LIBV4L: no libv4l libraries at all
> - without WITH_DYN_LIBV4L: only static libraries, no dynamic libraries
> And from configure --help:
> --disable-libv4l disable libv4l compilation
> --disable-dyn-libv4l disable dynamic libv4l support
This package is named "libv4l" in buildroot but repo name is "v4l-utils"
1) some library plugins on top of V4L kernel interface in order to
intercept user calls and hook/convert to the appropriate kernel call.
=> so called "libv4l" and located in "lib/" folder
2) some utilities located in "utils/" folder, such as the V4L compliancy
tool "v4l2-compliance" or the CEC compliancy tool "cec-compliance" which
are calling either the libv4l interface (default), the libv4l interface
but statically linked inside utilities (--disable-dyn-libv4l) or the V4L
kernel interface directly (--disable-libv4l).
Hope that helps to better understand the options.
>> But checking your log I see that --enable-shared is set, so it seems
>> that you are supporting shared libraries on no-MMU platform but without
>> fork() support, is my understanding correct ?
>> What you can do to fix build is to force disabling of libs inside libv4l
>> +ifeq ($(BR2_USE_MMU),)
>> +LIBV4L_CONF_OPTS += --disable-libv4l
> Works, but feels wrong: A package named libv4l enabled and building/installing
> nothing (except when LIBV4L_UTILS is enabled)...
The aim of the no-MMU dependency removal patchset was to enable build of
"utils" even on no-MMU platform. This is required to build at least the
2 mandatory compliancy tools:
- v4l-compliance: its test report is required by V4L maintainers and is
to be attached to the cover letter of any V4L driver pushed upstream.
- cec-compliance: the same for CEC drivers.
Please note that you cannot use the libv4l plugins mechanism without
having fork() support, see libv4lconvert/helper.c,
Means that only V4L utilities can be currently supported on no-MMU
Back to your exact build issue, the best fix on my opinion is to add a
dependency on fork() symbol in configure.ac instead of the one proposed
in libv4l.mk, find attached a patch proposal.
>> Hoping that helps.
>> Best regards,
>> On 07/11/2017 07:26 PM, Peter Seiderer wrote:
>>> Fixes :
>>> CXXLD v4l2-compliance
>>> .../output/build/libv4l-1.12.5/lib/libv4lconvert/.libs/libv4lconvert.so: undefined reference to `fork'
>>> collect2: error: ld returned 1 exit status
>>>  http://autobuild.buildroot.net/results/7e8/7e8fbd99a8c091d7bbeedd16066297682bbe29fe
>>> Signed-off-by: Peter Seiderer <ps.report at gmx.net>
>>> The libv4l build for noMMU platforms was enabled with commit 'package/libv4l:
>>> allow build of v4l2 utilities on noMMU platforms' (see ). But libv4lconvert uses
>>> fork internally, so all utils linking against fail to build. Fix this by disabling
>>> the utils on noMMU platforms (so keep building all libraries).
>>> Alternatives would be:
>>> - disable libv4l on all noMMU platforms (not only the utils), revert a part
>>> of commit 
>>> - create a patch to disable only libv4lconvert (and all dependend utils)
>>> on noMMU platforms
>>>  https://git.buildroot.net/buildroot/commit/?id=f837251785e9389f53d695ddb8a094707865171b
>>> package/libv4l/Config.in | 1 +
>>> 1 file changed, 1 insertion(+)
>>> diff --git a/package/libv4l/Config.in b/package/libv4l/Config.in
>>> index e7f78dc70f..61c290f251 100644
>>> --- a/package/libv4l/Config.in
>>> +++ b/package/libv4l/Config.in
>>> @@ -19,6 +19,7 @@ comment "libv4l JPEG support not enabled"
>>> config BR2_PACKAGE_LIBV4L_UTILS
>>> bool "v4l-utils tools"
>>> + depends on BR2_USE_MMU # fork(), used in libv4lconvert linked by various utils eg. v4l2-compliance
>>> v4l-utils is a collection of various video4linux and DVB utilities.
>>> Enable this if you want to build the following tools:
>> buildroot mailing list
>> buildroot at busybox.net
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