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 [off-list ref] wrote:

quoted

On 03/09/2015, 02:09 PM, Greg Kroah-Hartman wrote:

quoted

--- /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.)

quoted

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