Re: [OE-core] Need suggestions: in case where linux-lib-headers and the kernel versions differ

["Khem Raj" <raj.khem@gmail.com>]

On 4/23/21 8:03 AM, Sourabh Banerjee wrote:
> Hi All,
> I need your suggestion on how to reconcile if the linux-libc-headers and 
> kernel versions are different?
> For this discussion let's consider we are using the LTS branch YP-3.1 
> (Dunfell).
> With Dunfell let's consider following 3 cases:
> 
> 1) Machine is supported on 5.4 kernel
> *Kernel Recipe:* linux-yocto_5.4.bb
> *libc-headers:* meta/recipes-kernel/linux-libc-headers/linux-libc-headers_5.4.bb
>      There is no conflict in this case as libc-headers and linux-yocto 
> are on same version.
> 
> 2) Machine is supported on a higher kernel (let's say 5.10)
> *Kernel Recipe:* Let's assume provided by a BSP layer, linux_5.10.bb
> *libc-headers:* meta/recipes-kernel/linux-libc-headers/linux-libc-headers_5.4.bb
>      The kernel version is higher in this case. But, should be okay as 
> 5.10 UAPI is backward compatible and supports  
> linux-libc-headers_5.4 completely.
> 
> 3) Machine is supported on a lower kernel (let's say 4.19)
> Kernel Recipe: Let's assume provided by a BSP layer, linux_4.19.bb
> libc-headers: meta/recipes-kernel/linux-libc-headers/linux-libc-headers_5.4.bb
>      The kernel version is lower in this case. I suppose, this may lead 
> to some runtime issues? As the kernel built from 4.19 will not be able 
> to support 5.4 UAPI fully.
>      What's the recommendation here? Should the BSP provider port 
> linux-libc-header_4.19.bb in BSP layer and 
> set PREFERRED_VERSION_linux-libc-headers = "4.19%"
> 
>      I suspect this as UAPI headers such as following differ, and what 
> if this leads to runtime issues in case #3
>        -  videodev2.h: This header is enhanced in 5.4
>        -  fsverity.h : this header is not present in 4.19
> 

right. all this combos should work fine in general case, however they 
all are not tested with equal coverage. So best is always to try have 
UAPIs older or equal to the kernel you intend to use. Generally releases 
support supported LTS kernels and that should be good enough, however if 
you have very old kernel and want to use latest yocto release, be aware 
that we are not testing it with those old UAPIs so all testing falls on 
your in this regard.

> -- 
> Regards,
> Sourabh
> 
> 
> 
>