[poky] question about task override

[Tian, Kevin]

>From: Richard Purdie [mailto:richard.purdie at linuxfoundation.org]
>Sent: Wednesday, December 15, 2010 9:11 PM
>
>On Wed, 2010-12-15 at 03:24 -0800, Tian, Kevin wrote:
>> I'm not sure whether "task override" is the right term here. Let me describe it:
>>
>> It's possible to have multiple places define same task, e.g:
>>
>> a.bbclass:
>> 	do_install () {
>>      ...
>>      }
>>
>> b.bbclass:
>>      b_do_install() {
>>      ...
>>      }
>>
>> c.bb:
>> 	inherit a b
>>
>> I know that if c.bb defines its own do_install, that would be the one being used which
>> simply overrides a.bbclass and b.bbclass.
>>
>> However I don't know if c.bb doesn't define its own do_install, which one from a.bbclass
>> or b.bbclass will take effect here? In inherit order?
>
>As an example you will see base.bbclass defines base_do_install and then
>later there is EXPORT_FUNCTIONS do_install.
>
>What this means is that if there is no do_install defined,
>base_do_install also becomes do_install.
>
>The reason for this is that it means a recipe can define do_install and
>yet still call base_do_install.
>
>So in your above example, you'd really want c.bb to be able to do:
>
>do_install () {
>        a_do_install
>        b_do_install
>}

That's very clear. thanks.

>
>> A second question is how and where b_do_install is converted into a plain do_install. I tried
>> to search the source but failed to locate the exact lines. For example, patch_do_patch is
>> one mysterious function which I don't how it becomes do_patch.
>
>Its done with EXPORT_FUNCTIONS.
>
>> Then comes the third question. How to reference a specific version of do_install from
>> another place? I want to add one exclusive variable dependency for do_deploy in
>> kernel.bbclass, however neither of below works:
>>
>> (meta/conf/distro/poky.conf)
>> do_deploy[vardepsexclude] = "DATE TIME"
>> kernel_do_deploy[vardepsexclude] = "DATE TIME"
>>
>> There's one example in poky.conf:
>>
>> patch_do_patch[vardepsexclude] = "DATE SRCDATE"
>>
>> which works. Does that mean I have to change do_deploy in kernel.bbclass to
>> kernel_do_deploy which is unique in global namespace and then can be referenced
>> from other places?
>
>You should probably add
>
>do_deploy[vardepsexclude] = "DATE TIME"
>
>alongside the definition of the function in kernel.bbclass. If that
>doesn't work we need to work out why as it should.
>
>kernel.bbclass could change to be kernel_do_deploy and add an
>EXPORT_FUNCTION, we've just not had the need for a do_deploy() which
>called kernel_do_deploy() before.
>

OK, I'll try both methods. If both work I perhaps want to choose the later one which
makes all the relevant lines in one place for easy maintenance.

Thanks
Kevin