Re: [yocto] Out-of-tree Kernel Modules

[Quentin Schulz <quentin.schulz@cherry.de>]

Hi Yishai,

On 10/30/24 1:58 PM, Yishai Jaffe via lists.yoctoproject.org wrote:
> You don't often get email from yishai1999=gmail.com@lists.yoctoproject.org. Learn why this is important<https://aka.ms/LearnAboutSenderIdentification>
> Hi,
> I'm having a problem compiling my out of tree kernel module.
> I've managed to reproduce my problem with the meta-skeleton hello-mod recipe.
> I'm working with poky on branch scarthgap.
> Here are the necessary changes:
> 
> diff --git a/meta-skeleton/recipes-kernel/hello-mod/files/hello.c b/meta-skeleton/recipes-kernel/hello-mod/files/hello.c
> index 4f73455d20..221b5da97c 100644
> --- a/meta-skeleton/recipes-kernel/hello-mod/files/hello.c
> +++ b/meta-skeleton/recipes-kernel/hello-mod/files/hello.c
> @@ -7,9 +7,13 @@
>    *****************************************************************************/
> 
>   #include <linux/module.h>
> +#include <linux/sched/types.h>
> 
>   static int __init hello_init(void)
>   {
> + struct sched_param a = {
> + .sched_priority = 1,
> + };
>    pr_info("Hello World!\n");
>    return 0;
>   }
> 
> As you can see I'm trying to use the sched_param struct but when compiling I get the following error:
> 
> | /home/user/dev/yishai/yocto/build/tmp/work/qemux86_64-poky-linux/hello-mod/0.1/hello.c: In function 'hello_init':
> | /home/user/dev/yishai/yocto/build/tmp/work/qemux86_64-poky-linux/hello-mod/0.1/hello.c:14:16: error: variable 'a' has initializer but incomplete type
> |    14 |         struct sched_param a = {
> 
> This looks as if the struct isn't defined anywhere but if I look at tmp/work/qemux86_64-poky-linux/hello-mod/0.1/recipe-sysroot/usr/include/linux/sched/types.h which should be the header that I included - I can see that it is defined.
> Therefore, it seems like that is not the actual header being included.
> 
> Would love to get some help on this!
> 

Just giving hints at where to look at next, not sure this is really 
valuable information but here it is.

6.6 had the structure defined in include/uapi/linux/sched/types.h but 
6.7+ has it in include/linux/sched.h, c.f. 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d844fe65f0957024c3e1b0bf2a0615246184d9bc

If I am not mistaken, the kernel headers are coming from 
linux-libc-headers which would be 6.6 on Scarthgap, and not your kernel 
recipe (because it is **REALLY** bad to use non-upstream kernel headers, 
feel free to read the big comment in 
meta/recipes-kernel/linux-libc-headers/linux-libc-headers.inc :)

If that is the case, then you probably need to include 
uapi/linux/sched/types.h instead?

You probably need a different include for 6.7+ which would simply be 
include/sched.h?

Hope this helps.

Cheers,
Quentin