[yocto] Custom kernel headers and SDK

[Valentin Longchamp]

Hello William and Martin,

On 10/12/2015 15:53, William Mills wrote:
> 
> On 12/10/2015 09:40 AM, Vuille, Martin (Martin) wrote:
>> Hi Valentin,
>>
>> When we first encountered the need for custom kernel headers, I asked
>> a similar question to yours on this list. And what I learned from some of the
>> responses was that modifying the standard headers was fraught with
>> problems, including the issue that you raise.
>>
>> Fortunately, we got away without having to modify and export any standard
>> headers, so I dodged that bullet.
>>
>> Some ideas that come to mind:
>>
>> - Can you install your customized version in ${includedir}/XXX and use the
>>   include path search order to make sure the compiler sees it first?
> 
> This was the approach we used in a Debian based system.  Applications
> that needed to be dependent on the custom capabilities of our kernel
> depended on our XXX-kernel-header package and adjusted their include
> path to use it first.  All other apps continue to use the standard
> kernel headers.  (busybox or tar does not really care about our new
> wizbang feature and the Debian distro sure was not going to rebuild them
> just for us.)
> 
> I see no reason this could not work as well in an OE based distro.
> 
>>
>> - Can you include the standard header in a "wrapper" header and make your
>>   customizations in the wrapper instead?
>>
>> Regards,
>> MV

I just wanted to thank you for your answers and suggestion.

I have now used this approach and it works fine:
- make a new package that installs our changed linux-headers into another
directory than the linux-libc-headers
- added this package to TOOLCHAIN_TARGET_TASK so that it gets installed to the
SDK's sysroot
- changed the include path of the userspace applications that require these
changed headers and use the SDK so that they find them ($SDKTARGETSYSROOT helps
a lot here).

Valentin

>>
>>> -----Original Message-----
>>> From: Longchamp, Valentin [mailto:Valentin.Longchamp at keymile.com]
>>> Sent: December 10, 2015 4:47 AM
>>> To: Vuille, Martin (Martin); yocto at yoctoproject.org
>>> Cc: Brunck, Holger
>>> Subject: RE: Custom kernel headers and SDK
>>>
>>> Hi Martin,
>>>
>>> Thanks a lot for the suggestion. I had in the meantime come to a simliar
>>> solution: define a linux-XXX-headers recipe in our own meta layer where I
>>> install the missing kernel headers and then I add this linux-XXX-headers-dev
>>> package to our SDK's sysroot thanks to TARGET_TOOLCHAIN_TASK.
>>> Your implementation looks fine and I am going to pick some ideas from it.
>>>
>>> However, I have stumbled upon another problem with this approach: it
>>> works well if you add new files to the kernel headers. We unforntunately
>>> have at least one uapi file (i2c.h to name it) that is present in the standard
>>> kernel headers where we have our own version with some
>>> additions/extensions. If I install our version from ou linux-XXX-headers
>>> recipe, bitbake (correctly) complains that this file is provided by 2 packages
>>> (linux-libc-headers and linux-XXX-headers). And here I really don't know how
>>> to solve this issue. Any ideas/suggestions ?
>>>
>>> Thanks
>>>
>>> Valentin