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References: <20230117-kernel-kheaders-cpio-v1-1-058d3e1c8621@weissschuh.net>
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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Tue, 17 Jan 2023 23:33:30 +0900
Message-ID: <CAK7LNAQLBZOOjN7humBHKO9R3C5UGKfuSEX5dSEajt8KiSrAvQ@mail.gmail.com>
Subject: Re: [PATCH] kheaders: explicitly validate existence of cpio command
To:     =?UTF-8?Q?Thomas_Wei=C3=9Fschuh?= <thomas@t-8ch.de>
Cc:     =?UTF-8?Q?Thomas_Wei=C3=9Fschuh?= <linux@weissschuh.net>,
        linux-kbuild@vger.kernel.org,
        Amy Parker <apark0006@student.cerritos.edu>,
        linux-kernel@vger.kernel.org
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On Tue, Jan 17, 2023 at 10:19 PM Thomas Wei=C3=9Fschuh <thomas@t-8ch.de> wr=
ote:
>
> On Tue, Jan 17, 2023 at 09:46:02AM +0100, Nicolas Schier wrote:
> > On Tue, Jan 17, 2023 at 05:30:43AM +0000, Thomas Wei=C3=9Fschuh wrote:
> > > If the cpio command is not available the error emitted by
> > > gen_kheaders.so is not clear as all output of the call to cpio is
> > > discarded:
> > >
> > > GNU make 4.4:
> > >
> > >   GEN     kernel/kheaders_data.tar.xz
> > > find: 'standard output': Broken pipe
> > > find: write error
> > > make[2]: *** [kernel/Makefile:157: kernel/kheaders_data.tar.xz] Error=
 127
> > > make[1]: *** [scripts/Makefile.build:504: kernel] Error 2
> > >
> > > GNU make < 4.4:
> > >
> > >   GEN     kernel/kheaders_data.tar.xz
> > > make[2]: *** [kernel/Makefile:157: kernel/kheaders_data.tar.xz] Error=
 127
> > > make[2]: *** Waiting for unfinished jobs....
> > > make[1]: *** [scripts/Makefile.build:504: kernel] Error 2
> > >
> > > Add an explicit check that will trigger a clear message about the iss=
ue:
> > >
> > >   CHK     kernel/kheaders_data.tar.xz
> > > ./kernel/gen_kheaders.sh: line 17: type: cpio: not found
> >
> > Thanks for the patch!  What would you think about an even more verbose
> > message?  Perhaps something like:
> >
> >     echo >&2 ' *** "cpio" is required for "CONFIG_IKHEADERS". >&2
>
> Wouldn't hurt obviously.
> The other scripts used by the kernel don't seem to try to provide this
> kind of explicit message either, though.
> Having a line number, some sort of "not found" and the name of the
> command are enough, in my opinion.


Agree.  I am fine with this patch.


Just a side note.


'type' is defined in posix [1], so this code is portable.

Kbuild often uses "command -v" to check the existence of a command
because it is also posix compliant [2].


I just wondered why we did not use 'type' before...

'type' is more efficient because it is shell-builtin
(at least for dash and bash) but 'command' is not.


[1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/type.html

[2]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/command.htm=
l


>
> > Reviewed-by: Nicolas Schier <n.schier@avm.de>
>
> Thanks!
>
> Thomas


--=20
Best Regards
Masahiro Yamada