[yocto] kernel26 'machine feature'

[Darren Hart]

On 04/05/2012 02:05 PM, Denys Dmytriyenko wrote:
> On Thu, Apr 05, 2012 at 09:17:28PM +0100, Chris Tapp wrote:
>> On 5 Apr 2012, at 21:10, Gary Thomas wrote:
>>
>>> On 2012-04-05 14:02, Chris Tapp wrote:
>>>> Quite a few machine conf files specify the kernel26 machine feature. e.g., crownbay.conf has:
>>>>
>>>> MACHINE_FEATURES = "kernel26 screen keyboard pci usbhost ext2 ext3 x86 \
>>>>                     acpi serial usbgadget"
>>>>
>>>> What does this do? It's not listed at http://www.yoctoproject.org/docs/latest/poky-ref-manual/poky-ref-manual.html#ref-features-machine and seems to be at odds with:
>>>>
>>>> PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
>>>> PREFERRED_VERSION_linux-yocto = "3.0%"
>>>
>>> I don't think it does anything any more.  I'm pretty sure it used
>>> to be used to select which style of kernel module utilities to
>>> install (there was a change in kernel module format between 2.4
>>> and 2.6), but it seems that's gone now.  At least in the Poky/Yocto
>>> tree (oe-core + meta-yocto), there is no active use of this feature.
> 
> Yes, Classic OE (unlike OE-Core) used to support 2.4 and 2.6 kernels, hence 
> the use flag.
> 
>> Thanks, I was hoping it was something as simple as that.
>>
>> Another (possibly related) question - when the kernel built I noticed that 
>> linux_libc_headers_yocto-2.6.37 was 'mentioned' in the log output. Why was 
>> this used and not the headers for 3.0.18 ? The host is 2.6.32, so it doesn't 
>> look like is was for the tool chain.
> 
> Those are "user-space" kernel headers for libc. Those usually don't need to 
> match the exact kernel version, as APIs don't change that often between the 
> kernel and user-space. Unless you need some specific new API that got added in 
> the latest kernel...
> 

It's done this way to speed the build process as it uses a simple
tarball download of the kernel sources to do this. Ultimately I believe
we should build this package as part of the kernel build and PROVIDE it
as well.


-- 
Darren Hart
Intel Open Source Technology Center
Yocto Project - Linux Kernel