Selecting different kernel inside an image recipe

Selecting different kernel inside an image recipe

[Klaus Knopper]

Hello list,

I'm trying to build variantions/brands of an image that only differ in
kernel configuration and kernel modules included, but everything else stays
the same, for the exact same board, as in the main image.

Setting PREFERRED_PROVIDER_virtual/kernel = "different_kernel"
right inside in the new image recipe does not have any effect, as that
variable seems to be evaluated exclusively in the local.conf machine
file, which is read by all recipes.

I'm confident that it is somehow possible in yocto to create an
additional image recipe that only differs in kernel, but I'm missing the
HOWTO for this seemingly trivial task. :-(

Any hints/links?

With kind regards
-Klaus

Re: Selecting different kernel inside an image recipe

[Leonardo Sandoval]

On 07/08/2015 09:50 AM, Klaus Knopper wrote:
> Hello list,
>
> I'm trying to build variantions/brands of an image that only differ in
> kernel configuration and kernel modules included, but everything else stays
> the same, for the exact same board, as in the main image.
>
> Setting PREFERRED_PROVIDER_virtual/kernel = "different_kernel"
> right inside in the new image recipe does not have any effect, as that
> variable seems to be evaluated exclusively in the local.conf machine
> file, which is read by all recipes.

This variable is commonly used inside configuration metadata (machine or 
distro conf files). You may try it there.

>
> I'm confident that it is somehow possible in yocto to create an
> additional image recipe that only differs in kernel, but I'm missing the
> HOWTO for this seemingly trivial task. :-(
>
> Any hints/links?
>
> With kind regards
> -Klaus
>

Re: Selecting different kernel inside an image recipe

[Klaus Knopper]

Hello Leonardo,

On Wed, Jul 08, 2015 at 10:40:10AM -0500, Leonardo Sandoval wrote:
> On 07/08/2015 09:50 AM, Klaus Knopper wrote:
> >Hello list,
> >
> >I'm trying to build variantions/brands of an image that only differ in
> >kernel configuration and kernel modules included, but everything else stays
> >the same, for the exact same board, as in the main image.
> >
> >Setting PREFERRED_PROVIDER_virtual/kernel = "different_kernel"
> >right inside in the new image recipe does not have any effect, as that
> >variable seems to be evaluated exclusively in the local.conf machine
> >file, which is read by all recipes.
> 
> This variable is commonly used inside configuration metadata (machine or
> distro conf files). You may try it there.

Please help me to understand your answer: You are saying that I do have
to change the machine or distro config used for ALL recipes, to be able
to use a different kernel configuration in ONE recipe, right?

I was really trying to avoid that. :-(

So it is really not possible to just select a different kernel config
within a normal recipe without changing the global configuration?

Regards
-Klaus

Re: Selecting different kernel inside an image recipe

[Bruce Ashfield]

On 2015-07-08 12:36 PM, Klaus Knopper wrote:
> Hello Leonardo,
>
> On Wed, Jul 08, 2015 at 10:40:10AM -0500, Leonardo Sandoval wrote:
>> On 07/08/2015 09:50 AM, Klaus Knopper wrote:
>>> Hello list,
>>>
>>> I'm trying to build variantions/brands of an image that only differ in
>>> kernel configuration and kernel modules included, but everything else stays
>>> the same, for the exact same board, as in the main image.
>>>
>>> Setting PREFERRED_PROVIDER_virtual/kernel = "different_kernel"
>>> right inside in the new image recipe does not have any effect, as that
>>> variable seems to be evaluated exclusively in the local.conf machine
>>> file, which is read by all recipes.
>>
>> This variable is commonly used inside configuration metadata (machine or
>> distro conf files). You may try it there.
>
> Please help me to understand your answer: You are saying that I do have
> to change the machine or distro config used for ALL recipes, to be able
> to use a different kernel configuration in ONE recipe, right?
>
> I was really trying to avoid that. :-(
>
> So it is really not possible to just select a different kernel config
> within a normal recipe without changing the global configuration?

You really want a different kernel recipe to provide that different
kernel configuration.  Which looks to be what you are describing, and
you just want to switch the provider (again, what you are saying).

Changing the included kernel via that different kernel recipe/package
name, and setting it via the preferred provider is the same as any
bitbake variable.

So you should be able to set it in any .conf file, and then have what
you want. I've used layers with layer.conf files, and similar mechanisms
to do what you are trying in the past .. but the longer serving oe/bitbake
folks may have a better example to point at.

Cheers,

Bruce

>
> Regards
> -Klaus
>

Re: Selecting different kernel inside an image recipe

[Klaus Knopper]

Hello Bruce & list,

I need to come back to the topic after quite some failed attempts to
solve the problem of switching kernel configurations specific to an
image recipe.

On Wed, Jul 08, 2015 at 01:30:54PM -0400, Bruce Ashfield wrote:
> On 2015-07-08 12:36 PM, Klaus Knopper wrote:
> >Hello Leonardo,
> >
> >On Wed, Jul 08, 2015 at 10:40:10AM -0500, Leonardo Sandoval wrote:
> >>On 07/08/2015 09:50 AM, Klaus Knopper wrote:
> >>>Hello list,
> >>>
> >>>I'm trying to build variantions/brands of an image that only differ in
> >>>kernel configuration and kernel modules included, but everything else stays
> >>>the same, for the exact same board, as in the main image.
> >>>
> >>>Setting PREFERRED_PROVIDER_virtual/kernel = "different_kernel"
> >>>right inside in the new image recipe does not have any effect, as that
> >>>variable seems to be evaluated exclusively in the local.conf machine
> >>>file, which is read by all recipes.
> >>
> >>This variable is commonly used inside configuration metadata (machine or
> >>distro conf files). You may try it there.
> >
> >Please help me to understand your answer: You are saying that I do have
> >to change the machine or distro config used for ALL recipes, to be able
> >to use a different kernel configuration in ONE recipe, right?
> >
> >I was really trying to avoid that. :-(
> >
> >So it is really not possible to just select a different kernel config
> >within a normal recipe without changing the global configuration?
> 
> You really want a different kernel recipe to provide that different
> kernel configuration.  Which looks to be what you are describing, and
> you just want to switch the provider (again, what you are saying).

Yes, and I had indeed already added a new kernel recipe, which builds
the desired kernel as uImage when calling "bitbake kernel-recipename"
directly, but it's ignored by the image recipes. All of them use only
the kernel that's defined in build/conf/local.conf as
PREFERRED_PROVIDER_virtual/kernel . Redefining the variable in the image
recipes has no effect.

> Changing the included kernel via that different kernel recipe/package
> name, and setting it via the preferred provider is the same as any
> bitbake variable.

I thought so, but apparently I'mmissing something. It looks like
PREFERRED_PROVIDER_virtual/kernel only works in local.conf, i.e. I need
to fork the project or change the local.conf file each time I want to
use a different kernel. Is this a known or desired behavior?

> So you should be able to set it in any .conf file, and then have what
> you want.

So, can you confirm that it is not possible to set
PREFERRED_PROVIDER_virtual/kernel inside an image recipe?

> I've used layers with layer.conf files, and similar mechanisms
> to do what you are trying in the past .. but the longer serving oe/bitbake
> folks may have a better example to point at.

If there are examples for a more convenient way to switch kernels in a
recipe rather than inside a .conf file, please point me to the right
direction.

Regards
-Klaus

Re: Selecting different kernel inside an image recipe

[Trevor Woerner]

Hi Klaus,

On 08/04/15 00:15, Klaus Knopper wrote:
> So, can you confirm that it is not possible to set
> PREFERRED_PROVIDER_virtual/kernel inside an image recipe?

Confirmed, this is not possible.

I too thought it would make sense to choose one's kernel based on which
image you want to build. I was trying this a couple weeks ago and ran
into the exact same issue.

The way it was explained to me is as follows: your choice of kernel
affects a great many other "downstream" choices, therefore it needs to
be known early in the process of bitbake parsing your metadata. As a
result, there are only a few, select places where you can select your
kernel. Some of these include conf/local.conf, your distro.conf, and
your <machine>.conf. Unfortunately your <image>.conf is not one of them.

Also, if your distro or machine set the preferred kernel with an equals
sign, it is harder to override in your local.conf. In this case you
would need to try appending "_forcevariable" to your choice.

Best regards,
	Trevor

Re: Selecting different kernel inside an image recipe

[Mike Looijmans]

There are several solutions:

- Pick one kernel as the "master" one. Create recipes for alternative kernels 
as required, but blank the (R)PROVIDES so that they do not "provide" a kernel 
and bitbake will treat them as yet another package to build. In the scripts 
that you use to deploy the images, pick the kernel that you want.

- Create a new MACHINE for each alternative.

- Set up multiple build environments, share the sstate-cache and similar 
directories. Each environment can then pick its own kernel etc.


On 04-08-15 06:15, Klaus Knopper wrote:
> Hello Bruce & list,
>
> I need to come back to the topic after quite some failed attempts to
> solve the problem of switching kernel configurations specific to an
> image recipe.
>
> On Wed, Jul 08, 2015 at 01:30:54PM -0400, Bruce Ashfield wrote:
>> On 2015-07-08 12:36 PM, Klaus Knopper wrote:
>>> Hello Leonardo,
>>>
>>> On Wed, Jul 08, 2015 at 10:40:10AM -0500, Leonardo Sandoval wrote:
>>>> On 07/08/2015 09:50 AM, Klaus Knopper wrote:
>>>>> Hello list,
>>>>>
>>>>> I'm trying to build variantions/brands of an image that only differ in
>>>>> kernel configuration and kernel modules included, but everything else stays
>>>>> the same, for the exact same board, as in the main image.
>>>>>
>>>>> Setting PREFERRED_PROVIDER_virtual/kernel = "different_kernel"
>>>>> right inside in the new image recipe does not have any effect, as that
>>>>> variable seems to be evaluated exclusively in the local.conf machine
>>>>> file, which is read by all recipes.
>>>>
>>>> This variable is commonly used inside configuration metadata (machine or
>>>> distro conf files). You may try it there.
>>>
>>> Please help me to understand your answer: You are saying that I do have
>>> to change the machine or distro config used for ALL recipes, to be able
>>> to use a different kernel configuration in ONE recipe, right?
>>>
>>> I was really trying to avoid that. :-(
>>>
>>> So it is really not possible to just select a different kernel config
>>> within a normal recipe without changing the global configuration?
>>
>> You really want a different kernel recipe to provide that different
>> kernel configuration.  Which looks to be what you are describing, and
>> you just want to switch the provider (again, what you are saying).
>
> Yes, and I had indeed already added a new kernel recipe, which builds
> the desired kernel as uImage when calling "bitbake kernel-recipename"
> directly, but it's ignored by the image recipes. All of them use only
> the kernel that's defined in build/conf/local.conf as
> PREFERRED_PROVIDER_virtual/kernel . Redefining the variable in the image
> recipes has no effect.
>
>> Changing the included kernel via that different kernel recipe/package
>> name, and setting it via the preferred provider is the same as any
>> bitbake variable.
>
> I thought so, but apparently I'mmissing something. It looks like
> PREFERRED_PROVIDER_virtual/kernel only works in local.conf, i.e. I need
> to fork the project or change the local.conf file each time I want to
> use a different kernel. Is this a known or desired behavior?
>
>> So you should be able to set it in any .conf file, and then have what
>> you want.
>
> So, can you confirm that it is not possible to set
> PREFERRED_PROVIDER_virtual/kernel inside an image recipe?
>
>> I've used layers with layer.conf files, and similar mechanisms
>> to do what you are trying in the past .. but the longer serving oe/bitbake
>> folks may have a better example to point at.
>
> If there are examples for a more convenient way to switch kernels in a
> recipe rather than inside a .conf file, please point me to the right
> direction.
>
> Regards
> -Klaus
>



Kind regards,

Mike Looijmans
System Expert

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