Message-ID: <CA+r1ZhgasUAgS6LkF8z7E6JrfGOxxWV+dg1WtTNq4pJpnar8bg@mail.gmail.com>
Date:	Fri, 2 Oct 2015 12:35:03 -0700
From:	Jim Davis <jim.epost@...il.com>
To:	Alexander Kapshuk <alexander.kapshuk@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ver_linux: module-init-tools.patch

On Fri, Oct 2, 2015 at 12:03 PM, Alexander Kapshuk
<alexander.kapshuk@...il.com> wrote:
> On Fri, Oct 2, 2015 at 9:10 PM, Jim Davis <jim.epost@...il.com> wrote:
>> On Thu, Oct 1, 2015 at 11:49 AM, Alexander Kapshuk
>> <alexander.kapshuk@...il.com> wrote:
>>> The current implementation relies on 'depmod' to be available in the
>>> PATH. It also expects the version number to be found in the last field
>>> as seen by 'awk'. Should the output format be different, this approach
>>> would no longer be reliable.
>>>
>>> The proposed implementation locates 'depmod', and uses 'sed' as a more
>>> flexible tool to handle varying output formats.
>>>
>>> Tested on:
>>> Gentoo Linux
>>> Debian 6.0.10
>>> Oracle Linux Server release 7.1
>>> Arch Linux
>>> openSuSE 13.2
>>>
>>>
>>> Signed-off-by: Alexander Kapshuk <alexander.kapshuk@...il.com>
>>> ---
>>>
>>> --- linux/scripts/ver_linux.orig    2015-10-01 18:36:49.090519891 +0300
>>> +++ linux/scripts/ver_linux    2015-10-01 21:48:09.985628346 +0300
>>> @@ -25,7 +25,14 @@
>>>  echo -n "mount                  "
>>>  mount --version | awk '{print $NF}' | sed -e s/^mount-// -e s/\)$//
>>>
>>> -depmod -V  2>&1 | awk 'NR==1 {print "module-init-tools     ",$NF}'
>>> +depmod=`whereis depmod | awk '{print $2}'`
>>
>> Hmm.
>>
>> jim@...bstar:~$ which depmod
>> /usr/local/bin/depmod
>> jim@...bstar:~$ whereis depmod
>> depmod: /sbin/depmod /etc/depmod.d /usr/local/bin/depmod
>> /usr/share/man/man8/depmod.8.gz
>>
>> So while according to my $PATH preferences I'd rather run
>> /usr/local/bin/depmod, it looks like the '{print $2}' thing would pick
>> /sbin/depmod instead.
>>
>> Not a big deal, but I suspect those sort of considerations are why the
>> scripts tend just to check the $PATH.
>>
>> --
>> Jim
>
> Thanks for your feedback.
>
> Is '/sbin/depmod' perhaps a symlink to '/usr/local/bin/depmod' on your system?

No.  It's a contrived example, but /sbin/depmod and
/usr/local/bin/depmod are separate programs.  I can imagine a
developer wanting his or her own version for testing.

>
> On some distros, I found that 'which' may not necessarily locate the
> binary in question, because the $PATH is not set in a uniform fashion
> across various distros. Whereas 'whereis' was found to return a valid
> path to the binaries invoked by 'ver_linux' across all the distros I
> have been able to test-run 'ver_linux' on, especially on those where
> 'which' failed to do so. Which is something I found confusing
> considering the fact the manpages for both 'which' and 'whereis' claim
> to be searching the $PATH to find binaries.
>
> E.g. on Gentoo I get this:
>
> which depmod
> which: no depmod in
> (/usr/local/bin:/usr/bin:/bin:/opt/bin:/usr/i686-pc-linux-gnu/gcc-bin/4.8.5:/usr/games/bin:/home/alkap/bin:/usr/local/plan9/bin)
>
> whereis -b depmod
> depmod: /sbin/depmod
>
> ls -l /sbin/depmod
> lrwxrwxrwx 1 root root 9 Aug  8 14:47 /sbin/depmod -> /bin/kmod
>
> If you have a more reliable approach to suggest, I am open to suggestions.

I suspect it'll be hard to come up with something that's 100%
foolproof and respects user's choices.  Sticking with searching the
user's $PATH at least won't lead to surprises about which program is
being run...


-- 
Jim
--
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