managing layer priorities

managing layer priorities

[Tomas Frydrych]

Hi,

Is there a way to change the priority that a layer assigns itself in its
layer.conf? E.g., I want to add meta-oe alongside of meta-yocto, but I
want it to have a lower priority than the latter. Currently meta-yocto
gives itself "5" and meta-oe "6", I'd like to change this without having
to modify meta-oe/conf/layer.conf, but can't find a way to do this.

Tomas

Re: managing layer priorities

[Tomas Frydrych]

On 08/04/12 23:28, Tomas Frydrych wrote:
> Is there a way to change the priority that a layer assigns itself in its
> layer.conf? E.g., I want to add meta-oe alongside of meta-yocto, but I
> want it to have a lower priority than the latter. Currently meta-yocto
> gives itself "5" and meta-oe "6", I'd like to change this without having
> to modify meta-oe/conf/layer.conf, but can't find a way to do this.

Never mind, it is possible to override these in the last layer listed in
BBLAYERS.

Tomas

Re: managing layer priorities

[Gary Thomas]

On 2012-04-09 00:18, Tomas Frydrych wrote:
> On 08/04/12 23:28, Tomas Frydrych wrote:
>> Is there a way to change the priority that a layer assigns itself in its
>> layer.conf? E.g., I want to add meta-oe alongside of meta-yocto, but I
>> want it to have a lower priority than the latter. Currently meta-yocto
>> gives itself "5" and meta-oe "6", I'd like to change this without having
>> to modify meta-oe/conf/layer.conf, but can't find a way to do this.
>
> Never mind, it is possible to override these in the last layer listed in
> BBLAYERS.

How so?

-- 
------------------------------------------------------------
Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
------------------------------------------------------------

Re: managing layer priorities

[Tomas Frydrych]

On 09/04/12 14:04, Gary Thomas wrote:
> On 2012-04-09 00:18, Tomas Frydrych wrote:
>> On 08/04/12 23:28, Tomas Frydrych wrote:
>>> Is there a way to change the priority that a layer assigns itself in its
>>> layer.conf? E.g., I want to add meta-oe alongside of meta-yocto, but I
>>> want it to have a lower priority than the latter. Currently meta-yocto
>>> gives itself "5" and meta-oe "6", I'd like to change this without having
>>> to modify meta-oe/conf/layer.conf, but can't find a way to do this.
>>
>> Never mind, it is possible to override these in the last layer listed in
>> BBLAYERS.
> 
> How so?

You can set the various BBFILE_PRIORITY_**** and other variables in the
layer.conf for the last layer listed in your bblayers.conf. The layer
priorities get evaluated only after all of the layer.conf files have
been parsed, so anything that is set in the last layer.conf will be the
final value. I use the Yocto model where (unlike with OE layers) the
layer.conf prepends its layer path to BBPATH, so my custom layer is
last, but I imagine it would be possible to create a fake layer with no
recipes just for this specific purpose.

Tomas

> 

Re: managing layer priorities

[Paul Eggleton]

On Monday 09 April 2012 14:58:49 Tomas Frydrych wrote:
> On 09/04/12 14:04, Gary Thomas wrote:
> > On 2012-04-09 00:18, Tomas Frydrych wrote:
> >> On 08/04/12 23:28, Tomas Frydrych wrote:
> >>> Is there a way to change the priority that a layer assigns itself in its
> >>> layer.conf? E.g., I want to add meta-oe alongside of meta-yocto, but I
> >>> want it to have a lower priority than the latter. Currently meta-yocto
> >>> gives itself "5" and meta-oe "6", I'd like to change this without having
> >>> to modify meta-oe/conf/layer.conf, but can't find a way to do this.
> >> 
> >> Never mind, it is possible to override these in the last layer listed in
> >> BBLAYERS.
> > 
> > How so?
> 
> You can set the various BBFILE_PRIORITY_**** and other variables in the
> layer.conf for the last layer listed in your bblayers.conf. The layer
> priorities get evaluated only after all of the layer.conf files have
> been parsed, so anything that is set in the last layer.conf will be the
> final value. I use the Yocto model where (unlike with OE layers) the
> layer.conf prepends its layer path to BBPATH, so my custom layer is
> last, but I imagine it would be possible to create a fake layer with no
> recipes just for this specific purpose.

I realise what you're trying to do, but you should bear in mind when you do 
this you are relying on unintentional behaviour that may change in future.

There were some discussions at the recent BSP summit about improving bitbake 
so that layer priorities work in a more helpful manner. Also worth noting is 
that work to split up meta-oe is ongoing, so it may be in the near future that 
you don't have to shuffle layers around such that meta-oe doesn't have any 
undesired effects.

Cheers,
Paul

-- 

Paul Eggleton
Intel Open Source Technology Centre

Re: managing layer priorities

[Tomas Frydrych]

Hi Paul,

On 09/04/12 15:09, Paul Eggleton wrote:
> On Monday 09 April 2012 14:58:49 Tomas Frydrych wrote:
> I realise what you're trying to do, but you should bear in mind when you do 
> this you are relying on unintentional behaviour that may change in future.

I am not sure whether unintentional is an accurate description; layer
priority is explicitly and intentionally the function of other layers
due to inter-layer dependency. So I prefer to think of it as an
undocumented feature. :-) But I know, if it does not work, it's my own
fault.

The reason for doing this is that I'd like to be able to treat an
external layer as a read-only entity, and to enforce this. My experience
suggests that if you fork external layers alongside your custom layers,
this over time leads to unnecessary maintenance costs. On the other
hand, if each external layer is a read-only entity, it can be integrated
as a read-only git submodule, and no naughty developers will then make
changes to it.

Tomas