linux-kernel - Re: [PATCH 13/14] kdbus: add walk-through user space example

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Date:	Tue, 24 Mar 2015 18:37:26 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	David Herrmann <dh.herrmann@...il.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Tom Gundersen <teg@...m.no>, Jiri Kosina <jkosina@...e.cz>,
	Andy Lutomirski <luto@...capital.net>,
	Linux API <linux-api@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Daniel Mack <daniel@...que.org>,
	Djalal Harouni <tixxdz@...ndz.org>,
	Michal Marek <mmarek@...e.cz>, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH 13/14] kdbus: add walk-through user space example

Ccing kbuild fellows (see the very bottom).

On 03/24/2015, 06:15 PM, David Herrmann wrote:
> Hi
> 
> On Tue, Mar 24, 2015 at 5:46 PM, Jiri Slaby <jslaby@...e.cz> wrote:
>> On 03/09/2015, 02:09 PM, Greg Kroah-Hartman wrote:
>>> --- /dev/null
>>> +++ b/samples/kdbus/Makefile
>>> @@ -0,0 +1,10 @@
>>> +# kbuild trick to avoid linker error. Can be omitted if a module is built.
>>> +obj- := dummy.o
>>> +
>>> +hostprogs-y += kdbus-workers
>>> +
>>> +always := $(hostprogs-y)
>>
>> Errr, no. Not only it causes build failures (even with KDBUS=n), it
>> definitely should not be built for everyone.
> 
> It's only built if CONFIG_SAMPLES is set, right?

Yes, but I build other samples selected with separate CONFIG_ options
like CONFIG_SAMPLE_LIVEPATCH. So this guy should have its own CONFIG_
option too, because I (and likely others) don't want to build it. All of
the samples should be protected at least by their respective kernel
CONFIG_ option IMO.

> What build-failures does it cause? linux/kdbus.h is not optional based
> on CONFIG_KDBUS, so the samples should build just fine. Can you tell
> me what kind of errors you get? The kbuild-robots didn't report
> anything so far.

The output is this:
In file included from samples/kdbus/kdbus-workers.c:79:0:
/home/latest/linux/samples/kdbus/kdbus-api.h:5:25: fatal error:
linux/kdbus.h: No such file or directory
 #include <linux/kdbus.h>
                         ^
compilation terminated.

I now know that I have to install_headers *if* I want to build the
sample. But I don't want to build it in the first place. (So the config
option above should be all we need.)

>> And why is it a host prog? It's a sample prog for the kernel I am
>> building, i.e. for the destination arch, like all the other samples.
> 
> It's modeled after the other user-space examples in ./samples/, which
> all use hostprogs (see samples/{bpf,hidraw,seccomp,uhid}/Makefile). I
> have no idea how to build programs that run on the target
> architecture. Documentation/kbuild/makefiles.txt doesn't list it,
> which is, I guess, the reason why everyone used hostprogs so far. And
> given that autotools calls the target architecture "--host", I
> actually thought this is what hostprogs does.. apparently that's not
> the case, sorry.

Oh, it's cut&paste, I see. This does not look correct though. The hack
inclusive. Host progs are intended to be run on the host where the
kernel is built. During the compilation or such (like x/menuconfig).
Quite misleading naming if you are used to the autotools one.

thanks,
-- 
js
suse labs
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