Re: [yocto] more nitpicky pedantry: question about DEFAULT_PREFERENCE

Re: [yocto] more nitpicky pedantry: question about DEFAULT_PREFERENCE

[rpjday]

On Sat, 8 Feb 2020, rpjday@crashcourse.ca wrote:
... snip ...
> which seems odd as there don't appear to be any other recipes that
> provide pkgconfig, and AIUI, the default provider for any recipe is
> the recipe with *exactly* the same name as the target -- in this case,
> "pkgconfig".
...

  also wanted to clarify, while the default provider of a dependency
is the recipe with *exactly* that name, i'm assuming (i think i
remember this from somewhere) that if you have a number of recipes
that all provide, say, "virtual/kernel", and you have an explicit
dependency of "virtual/kernel", you *must* supply a

  PREFERRED_PROVIDER_virtual/kernel = ...

line, yes? as in, there's no weird processing to figure out which
recipe you'll be arbitrarily handed among the several that could be
used.

rday

Re: [yocto] more nitpicky pedantry: question about DEFAULT_PREFERENCE

[Richard Purdie]

On Sat, 2020-02-08 at 13:48 -0500, rpjday@crashcourse.ca wrote:
> On Sat, 8 Feb 2020, rpjday@crashcourse.ca wrote:
> ... snip ...
> > which seems odd as there don't appear to be any other recipes that
> > provide pkgconfig, and AIUI, the default provider for any recipe is
> > the recipe with *exactly* the same name as the target -- in this
> > case,
> > "pkgconfig".
> ...
> 
>   also wanted to clarify, while the default provider of a dependency
> is the recipe with *exactly* that name, i'm assuming (i think i
> remember this from somewhere) that if you have a number of recipes
> that all provide, say, "virtual/kernel", and you have an explicit
> dependency of "virtual/kernel", you *must* supply a
> 
>   PREFERRED_PROVIDER_virtual/kernel = ...
> 
> line, yes? as in, there's no weird processing to figure out which
> recipe you'll be arbitrarily handed among the several that could be
> used.

The resolution code is deterministic (i.e. it might sort them) but
there is no specific default provider, no.

Cheers,

Richard

Re: [yocto] more nitpicky pedantry: question about DEFAULT_PREFERENCE

[rpjday]

On Mon, 10 Feb 2020, Richard Purdie wrote:

> On Sat, 2020-02-08 at 13:48 -0500, rpjday@crashcourse.ca wrote:
> > On Sat, 8 Feb 2020, rpjday@crashcourse.ca wrote:
> > ... snip ...
> > > which seems odd as there don't appear to be any other recipes that
> > > provide pkgconfig, and AIUI, the default provider for any recipe is
> > > the recipe with *exactly* the same name as the target -- in this
> > > case,
> > > "pkgconfig".
> > ...
> >
> >   also wanted to clarify, while the default provider of a dependency
> > is the recipe with *exactly* that name, i'm assuming (i think i
> > remember this from somewhere) that if you have a number of recipes
> > that all provide, say, "virtual/kernel", and you have an explicit
> > dependency of "virtual/kernel", you *must* supply a
> >
> >   PREFERRED_PROVIDER_virtual/kernel = ...
> >
> > line, yes? as in, there's no weird processing to figure out which
> > recipe you'll be arbitrarily handed among the several that could be
> > used.
>
> The resolution code is deterministic (i.e. it might sort them) but
> there is no specific default provider, no.

  ah, so if you don't specify a PREFERRED_PROVIDER, then *some*
provider will ultimately be selected, is that it? you just won't have
any gurarantee which one it will be.

rday

Re: [yocto] more nitpicky pedantry: question about DEFAULT_PREFERENCE

[rpjday]

On Mon, 10 Feb 2020, Richard Purdie wrote:

> On Sat, 2020-02-08 at 13:31 -0500, rpjday@crashcourse.ca wrote:

> >    consider under recipes-devtools the two directories "pkgconfig"
> > and "pkgconf", and the respective .bb files:
> >
> >   - pkgconfig_git.bb
> >   - pkgconf_1.6.3.bb
> >
> > the pkgconfig recipe file does *not* contain a PROVIDES setting,
> > while pkgconfig_1.6.3.bb does:
> >
> >   PROVIDES += "pkgconfig"
>
> The above looks superfluous at a glance.

  sorry, i mistyped the above, i should have written:

  "the pkgconfig recipe file does *not* contain a PROVIDES setting,
  while pkgconf_1.6.3.bb does:"

so that PROVIDES line *would* be necessary, yes? (just not the "+="
part).  my apologies for reproducing incorrectly.

rday

Re: [yocto] more nitpicky pedantry: question about DEFAULT_PREFERENCE

[Richard Purdie]

On Sat, 2020-02-08 at 13:31 -0500, rpjday@crashcourse.ca wrote:
>   (part of the nitpickiness of some of these questions stems from
> that, in my updated courseware, i want to use actual examples out of,
> say, the openembedded layer, and not just contrived examples
> involving
> packages like "foo" and "bar". to that end, i want to be able to
> explain why some recipes are written the way they are and,
> conversely,
> to explain why some recipes might look weird.)
> 
>   the bitbake manual has a reasonable explanation of
> DEFAULT_PREFERENCE but there are examples in the OE layer that seem
> to
> not be written as cleanly as they could be.
> 
>    consider under recipes-devtools the two directories "pkgconfig"
> and
> "pkgconf", and the respective .bb files:
> 
>   - pkgconfig_git.bb
>   - pkgconf_1.6.3.bb
> 
> the pkgconfig recipe file does *not* contain a PROVIDES setting,
> while pkgconfig_1.6.3.bb does:
> 
>   PROVIDES += "pkgconfig"

It doesn't, pkgconf_1.6.3.bb does, which is quite different and it then
makes sense.

Cheers,

Richard

Re: [yocto] more nitpicky pedantry: question about DEFAULT_PREFERENCE

[Richard Purdie]

On Sat, 2020-02-08 at 13:31 -0500, rpjday@crashcourse.ca wrote:
>   (part of the nitpickiness of some of these questions stems from
> that, in my updated courseware, i want to use actual examples out of,
> say, the openembedded layer, and not just contrived examples
> involving
> packages like "foo" and "bar". to that end, i want to be able to
> explain why some recipes are written the way they are and,
> conversely,
> to explain why some recipes might look weird.)
> 
>   the bitbake manual has a reasonable explanation of
> DEFAULT_PREFERENCE but there are examples in the OE layer that seem
> to
> not be written as cleanly as they could be.
> 
>    consider under recipes-devtools the two directories "pkgconfig"
> and
> "pkgconf", and the respective .bb files:
> 
>   - pkgconfig_git.bb
>   - pkgconf_1.6.3.bb
> 
> the pkgconfig recipe file does *not* contain a PROVIDES setting,
> while pkgconfig_1.6.3.bb does:
> 
>   PROVIDES += "pkgconfig"

The above looks superfluous at a glance. 

> so, given that, one expects that other recipes should have a
> DEPENDency on "pkgconfig", which could be satisfied by either of
> those.
> 
>   however, oddly, the file pkgconf_1.6.3.bb contains the line:
> 
>   DEFAULT_PREFERENCE = "-1"
>
> which seems odd as there don't appear to be any other recipes that
> provide pkgconfig, and AIUI, the default provider for any recipe is
> the recipe with *exactly* the same name as the target -- in this
> case, "pkgconfig".

DEFAULT_PREFERENCE works against versions, not providers.
I'm not sure what that line is trying to do but I also suspect its superfluous.

>   so while that DEFAULT_PREFERENCE line doesn't hurt anything, in
> this specific case (assuming i haven't overlooked any other recipes
> that provide pkgconfig), that DEFAULT_PREFERENCE line is superfluous,
> correct?

For different reasoning, yes :)

Cheers,

Richard