linux-kernel - Re: [PATCH v2 2/2] perf tools: Default to python version 2

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Date:	Sat, 02 Aug 2014 12:56:48 +0200
From:	Thomas Ilsche <thomas.ilsche@...dresden.de>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Thomas Ilsche <thomas.ilsche@...dresden.de>
Subject: Re: [PATCH v2 2/2] perf tools: Default to python version 2


Zitat von Arnaldo Carvalho de Melo <acme@...nel.org>:

> Em Tue, Jul 29, 2014 at 03:57:20PM +0900, Namhyung Kim escreveu:
>> According to PEP 394 recommendation [1], it's more portable to use
>> python2 rather than plain python to refer python binary version 2.
>>
>> Since there're distros using python3 by default like Arch, and we
>> don't support python3 (yet), it'd be better using python2 explicitly.
>>
>> But older versions (prior to 2.7) seem not to provide python2 but just
>> python.  Given that it's only old version, try python2 first and then
>> fallback to python.  It'll ensure that it always points to python 2.x.
>
> It should fallback, right?

Yes.

> [acme@...ora14 linux]$ ls -la /usr/bin/python2-config
> ls: cannot access /usr/bin/python2-config: No such file or directory
> [acme@...ora14 linux]$ ls -la /usr/bin/python-config
> lrwxrwxrwx. 1 root root 16 Mar 25 09:43 /usr/bin/python-config ->  
> python2.7-config

Appearently this fedora package symlinks python -> python2 but does not so for
python2-config. The Makefile looks for either python2 or python as fallback and
then assumes that a respective "-config" exists. I think this is a sane assumption.

I guess if this needs to be supported, there needs to be another fallback if
$(PYTHON)-config is not found to try python-config again. However this may
behave weirdly if someone has python2, no python2-devel but python3-devel
installed, sets PYTHON=python2 and then still gets a version error. Or we
somehow only fallback if no PYTHON is specified (not sure how to implemented
that elegantly).

Best,
Thomas


> [acme@...ora14 linux]$ rpm -qf /usr/bin/python-config
> python-devel-2.7-8.fc14.1.x86_64
> [acme@...ora14 linux]$ cat /etc/fedora-release
> Fedora release 14 (Laughlin)
> [acme@...ora14 linux]$
>
> [acme@...ora14 linux]$ time make O=/tmp/build/perf -C tools/perf install
> make: Entering directory `/home/acme/git/linux/tools/perf'
>   BUILD:   Doing 'make -j4' parallel build
> config/Makefile:126: The path '/usr/bin/python2-config' is not executable.
> config/Makefile:339: No libdw DWARF unwind found, Please install
> elfutils-devel/libdw-dev >= 0.158 and/or set LIBDW_DIR
> config/Makefile:481: Missing perl devel files. Disabling perl scripting
> support, consider installing perl-ExtUtils-Embed
> config/Makefile:512: No python-config tool was found
> config/Makefile:512: Python support will not be built
>
>> [1] https://www.python.org/dev/peps/pep-0394
>>
>> Suggested-by: Thomas Ilsche <thomas.ilsche@...dresden.de>
>> Tested-by: Thomas Ilsche <thomas.ilsche@...dresden.de>
>> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
>> ---
>>  tools/perf/config/Makefile | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/perf/config/Makefile b/tools/perf/config/Makefile
>> index e05d8f99424d..60177278a357 100644
>> --- a/tools/perf/config/Makefile
>> +++ b/tools/perf/config/Makefile
>> @@ -121,8 +121,8 @@ ifdef PARSER_DEBUG
>>  endif
>>
>>  ifndef NO_LIBPYTHON
>> -  override PYTHON := \
>> -    $(call get-executable-or-default,PYTHON,python)
>> +  PYTHON2 := $(if $(call get-executable,python2),python2,python)
>> +  override PYTHON := $(call get-executable-or-default,PYTHON,$(PYTHON2))
>>    override PYTHON_CONFIG := \
>>      $(call get-executable-or-default,PYTHON_CONFIG,$(PYTHON)-config)
>>
>> --
>> 2.0.0





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