Patchwork [1/1] Create a symbolic link to the target kernel directory.

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Submitter Sagaert Johan
Date Nov. 1, 2012, 12:17 a.m.
Message ID <1351729065-31324-1-git-send-email-sagaert.johan@skynet.be>
Download mbox | patch
Permalink /patch/196062/
State Rejected
Headers show

Comments

Sagaert Johan - Nov. 1, 2012, 12:17 a.m.
This symbolic link makes it easier when building kernel modules.
The makefile for a module no longer has to point to the full directory name of the kernel but can use this symbolic link instead.
You no longer need to edit the path to the kernel tree in the module's makefiles when changing your target kernel version.

Signed-off-by: Sagaert Johan <sagaert.johan@skynet.be>
---
 Makefile       | 1 +
 linux/linux.mk | 2 ++
 2 files changed, 3 insertions(+)
Arnout Vandecappelle - Nov. 1, 2012, 1:07 a.m.
On 11/01/12 01:17, Sagaert Johan wrote:
> This symbolic link makes it easier when building kernel modules.
> The makefile for a module no longer has to point to the full directory name of the kernel but can use this symbolic link instead.
> You no longer need to edit the path to the kernel tree in the module's makefiles when changing your target kernel version.

  I don't see the point...  What's wrong with passing KERNELDIR=$(LINUX_DIR) to
the sub-make in the .mk file?  Cfr. lttng-modules.

  Regards,
  Arnout
Sagaert Johan - Nov. 1, 2012, 1:14 a.m.
Hi Arnout

I always build modules outside of the buildroot system.
Is there another (fast ) way ? I don't like to wait 20 seconds for buildroot tarring the rootfs. 

Johan

-----Oorspronkelijk bericht-----
Van: buildroot-bounces@busybox.net [mailto:buildroot-bounces@busybox.net] Namens Arnout Vandecappelle
Verzonden: donderdag 1 november 2012 2:08
Aan: Sagaert Johan
CC: buildroot@busybox.net
Onderwerp: Re: [Buildroot] [PATCH 1/1] Create a symbolic link to the target kernel directory.

On 11/01/12 01:17, Sagaert Johan wrote:
> This symbolic link makes it easier when building kernel modules.
> The makefile for a module no longer has to point to the full directory name of the kernel but can use this symbolic link instead.
> You no longer need to edit the path to the kernel tree in the module's makefiles when changing your target kernel version.

  I don't see the point...  What's wrong with passing KERNELDIR=$(LINUX_DIR) to the sub-make in the .mk file?  Cfr. lttng-modules.

  Regards,
  Arnout
Thomas Petazzoni - Nov. 1, 2012, 9:19 a.m.
On Thu, 1 Nov 2012 02:14:35 +0100, Sagaert Johan wrote:

> I always build modules outside of the buildroot system.
> Is there another (fast ) way ? I don't like to wait 20 seconds for
> buildroot tarring the rootfs. 

I don't see the relation between waiting 20 seconds for Buildroot to
tar the rootfs and the patch you're posting. Care to explain?

Thomas
Sagaert Johan - Nov. 1, 2012, 7:10 p.m.
Hi

An example makefile explains it all :

With my patch I can write a makefile for my kernel modules like this:

MODULENAME := digitalio

obj-m += $(MODULENAME).o

KERNELDIR=/home/buildroot12git/targetkernel

all:$(MODULENAME).ko

$(MODULENAME).ko:$(MODULENAME).c
	make -C $(KERNELDIR) SUBDIRS=$(PWD) modules CC=arm-linux-gcc LD=arm-linux-ld ARCH=arm

.PHONY clean:
	make -C $(KERNELDIR) M=$(PWD) clean




Without the symbolic link I had to use this makefile, and change it everytime I used another kernel version.

MODULENAME := digitalio

obj-m += $(MODULENAME).o

KERNELDIR=/home/buildroot12git/output/build/linux-76e10d158efb6d4516018846f60c2ab5501900bc

all:$(MODULENAME).ko

$(MODULENAME).ko:$(MODULENAME).c
	make -C $(KERNELDIR) SUBDIRS=$(PWD) modules CC=arm-linux-gcc LD=arm-linux-ld ARCH=arm

.PHONY clean:
	make -C $(KERNELDIR) M=$(PWD) clean 


As I onderstood from Arnout, I could build the module from within buildroot (making use of the buildroot vars) but this not an
option while still developing a module. Every buildroot make would also force a regeneration of the rootfs tar, and this takes a
serious ammount of time with a large rootfs.
So I develop it outside the build system and use the symlink to the kernel I have selected.

Regards, Johan

-----Oorspronkelijk bericht-----
Van: Thomas Petazzoni [mailto:thomas.petazzoni@free-electrons.com] 
Verzonden: donderdag 1 november 2012 10:19
Aan: Sagaert Johan
CC: 'Arnout Vandecappelle'; buildroot@busybox.net
Onderwerp: Re: [Buildroot] [PATCH 1/1] Create a symbolic link to the target kernel directory.


On Thu, 1 Nov 2012 02:14:35 +0100, Sagaert Johan wrote:

> I always build modules outside of the buildroot system.
> Is there another (fast ) way ? I don't like to wait 20 seconds for 
> buildroot tarring the rootfs.

I don't see the relation between waiting 20 seconds for Buildroot to tar the rootfs and the patch you're posting. Care to explain?

Thomas
--
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux development, consulting, training and support.
http://free-electrons.com
Thomas Petazzoni - Nov. 1, 2012, 10:24 p.m.
Dear Sagaert Johan,

On Thu, 1 Nov 2012 20:10:26 +0100, Sagaert Johan wrote:

> KERNELDIR=/home/buildroot12git/output/build/linux-76e10d158efb6d4516018846f60c2ab5501900bc

Turn this into:

KERNELDIR=$(shell ls -1 /home/buildroot12git/output/build/linux-[0-9a-f]*)

or, if you want something cleaner, add a <pkg>-show-builddir target for
all packages in pkg-generic.mk (we could probably get this patch
upstream), and do:

KERNELDIR=($shell make -C /home/buildroot12git/ linux-show-builddir)

And voilĂ .

Thomas

Patch

diff --git a/Makefile b/Makefile
index 0128839..8356aeb 100644
--- a/Makefile
+++ b/Makefile
@@ -668,6 +668,7 @@  ifeq ($(O),output)
 	rm -rf $(O)
 endif
 	rm -rf $(CONFIG_DIR)/.config $(CONFIG_DIR)/.config.old $(CONFIG_DIR)/.auto.deps
+	rm -f targetkernel 
 
 cross: $(BASE_TARGETS)
 
diff --git a/linux/linux.mk b/linux/linux.mk
index c4bdf90..4541081 100644
--- a/linux/linux.mk
+++ b/linux/linux.mk
@@ -219,6 +219,8 @@  define LINUX_BUILD_CMDS
 	fi
 	$(LINUX_BUILD_DTB)
 	$(LINUX_APPEND_DTB)
+	rm -f targetkernel
+	ln -s $(LINUX_DIR) targetkernel
 endef