Difference between bitbake inclusion and inheritance

Difference between bitbake inclusion and inheritance

[Davis Roman]

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Hello,

I'm a yocto newbie and so I'm becoming familiar with the documentation.

I came across a bitbake feature that is somewhat confusing to me regarding
the difference between optional/required inclusion versus inheritance.

As far as optional/required inclusion is concerned, the documentation
states quite clearly that the main difference is that the former will not
issue an error message if the specified file is not found while the latter
will so there is no issue here.

My issue has to do with the 'inherit' command. Sounds to me like 'include'
and 'require' already do the trick so I'm curious to know what value does
'inherit' bring ?

Any clarification would be extremely appreciated.

Thank you,

Davis

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Re: Difference between bitbake inclusion and inheritance

[Khem Raj]

On Tue, Oct 18, 2016 at 3:37 PM, Davis Roman <davis.roman84@gmail.com> wrote:
> Hello,
>
> I'm a yocto newbie and so I'm becoming familiar with the documentation.
>
> I came across a bitbake feature that is somewhat confusing to me regarding
> the difference between optional/required inclusion versus inheritance.
>
> As far as optional/required inclusion is concerned, the documentation states
> quite clearly that the main difference is that the former will not issue an
> error message if the specified file is not found while the latter will so
> there is no issue here.
>
> My issue has to do with the 'inherit' command. Sounds to me like 'include'
> and 'require' already do the trick so I'm curious to know what value does
> 'inherit' bring ?

you can override pretty much everything from an inherited class if you wish to

>
> Any clarification would be extremely appreciated.
>
> Thank you,
>
> Davis
>
> --
> _______________________________________________
> yocto mailing list
> yocto@yoctoproject.org
> https://lists.yoctoproject.org/listinfo/yocto
>

Re: Difference between bitbake inclusion and inheritance

[Paul Eggleton]

Hi Davis,

On Tue, 18 Oct 2016 18:37:50 Davis Roman wrote:
> I'm a yocto newbie and so I'm becoming familiar with the documentation.
> 
> I came across a bitbake feature that is somewhat confusing to me regarding
> the difference between optional/required inclusion versus inheritance.
> 
> As far as optional/required inclusion is concerned, the documentation
> states quite clearly that the main difference is that the former will not
> issue an error message if the specified file is not found while the latter
> will so there is no issue here.
> 
> My issue has to do with the 'inherit' command. Sounds to me like 'include'
> and 'require' already do the trick so I'm curious to know what value does
> 'inherit' bring ?

The answer is that they are very similar - but tend to be used for slightly 
different purposes. inherit is for where you have some functionality that you 
expect to be applicable across a number of recipes, so it should show up in a 
standard location in a reasonably standard format. The technical differences 
really stem from that:

* Classes must appear in a classes subdirectory somewhere along BBPATH
* Classes must be named <something>.bbclass
* Classes can use EXPORT_FUNCTIONS so you can still call the original function 
from your overridden version
* It's easy to query from python code whether a recipe inherits a class (and 
it's something we do in quite a number of places); it's technically possible 
to do the same for include/require but more difficult

include/require are much more generic and applicable for any other kind of 
shared or encapsulated functionality or configuration that doesn't suit a 
.bbclass.

Note that not all classes are typically inherited from individual recipes with 
inherit - there are classes that are usually applied globally by adding their 
names to INHERIT (e.g. buildhistory).

Hope that helps.

Cheers,
Paul

-- 

Paul Eggleton
Intel Open Source Technology Centre

Re: Difference between bitbake inclusion and inheritance

[Davis Roman]

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Hi Khem, Paul

I understand now.

Thank you both for your answers!

- Davis

On Tue, Oct 18, 2016 at 10:00 PM, Paul Eggleton <
paul.eggleton@linux.intel.com> wrote:

> Hi Davis,
>
> On Tue, 18 Oct 2016 18:37:50 Davis Roman wrote:
> > I'm a yocto newbie and so I'm becoming familiar with the documentation.
> >
> > I came across a bitbake feature that is somewhat confusing to me
> regarding
> > the difference between optional/required inclusion versus inheritance.
> >
> > As far as optional/required inclusion is concerned, the documentation
> > states quite clearly that the main difference is that the former will not
> > issue an error message if the specified file is not found while the
> latter
> > will so there is no issue here.
> >
> > My issue has to do with the 'inherit' command. Sounds to me like
> 'include'
> > and 'require' already do the trick so I'm curious to know what value does
> > 'inherit' bring ?
>
> The answer is that they are very similar - but tend to be used for slightly
> different purposes. inherit is for where you have some functionality that
> you
> expect to be applicable across a number of recipes, so it should show up
> in a
> standard location in a reasonably standard format. The technical
> differences
> really stem from that:
>
> * Classes must appear in a classes subdirectory somewhere along BBPATH
> * Classes must be named <something>.bbclass
> * Classes can use EXPORT_FUNCTIONS so you can still call the original
> function
> from your overridden version
> * It's easy to query from python code whether a recipe inherits a class
> (and
> it's something we do in quite a number of places); it's technically
> possible
> to do the same for include/require but more difficult
>
> include/require are much more generic and applicable for any other kind of
> shared or encapsulated functionality or configuration that doesn't suit a
> .bbclass.
>
> Note that not all classes are typically inherited from individual recipes
> with
> inherit - there are classes that are usually applied globally by adding
> their
> names to INHERIT (e.g. buildhistory).
>
> Hope that helps.
>
> Cheers,
> Paul
>
> --
>
> Paul Eggleton
> Intel Open Source Technology Centre
>

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