Re: [OE-core] why "PREFERRED_PROVIDER_udev" and not "PREFERRED_PROVIDER_virtual/udev"?

Re: [OE-core] why "PREFERRED_PROVIDER_udev" and not "PREFERRED_PROVIDER_virtual/udev"?

[Robert P. J. Day]

On Mon, 30 Aug 2021, Robert P. J. Day wrote:

>   i was going to extend section 3.3.17, "Using Virtual Providers",
> with an intro example using "udev" until i realized that that
> example doesn't use the "virtual/" notation. so ... why not? is
> there some distinction between other components that use the
> "virtual/" prefix, but a reason that one does not specify:
>
>   PROVIDES = "virtual/udev"
>
> rather than just:
>
>   PROVIDES = "udev"
>
> and then use the corresponding PREFERRED_PROVIDER_virtual/udev
> notation?

  just to make sure folks understand what i'm getting at, the section:

https://docs.yoctoproject.org/dev-manual/common-tasks.html#using-virtual-providers

opens with, "Prior to a build, if you know that several different
recipes provide the same functionality, you can use a virtual provider
(i.e. virtual/*) as a placeholder for the actual provider."

  except there are cases where several different recipes provide the
same functionality that *don't* incorporate the "virtual/" notation,
so which ones merit that and which ones don't? (i mentioned "udev"
being provided by both "eudev" and "systemd", for which i wrote an
utterly brilliant explanation that i now realize isn't appropriate for
that section.)

  in the simpler cases, you have recipes that have a new name that
can now be used in place of the old, such that "stress-ng" provides
"stress", so you don't have to mess with all your old images and
packagegroups. and in situations like that, the "virtual/" notation
would seem out of place.

  OTOH, well, virtual "kernel" and "bootloader" makes perfect sense as
they represent a more abstract idea. so ... thoughts? even though
"udev" does not use the "virtual/" notation, would it still fall under
the category of "virtual provider"? if not, how would one describe it?

rday

Re: [OE-core] why "PREFERRED_PROVIDER_udev" and not "PREFERRED_PROVIDER_virtual/udev"?

[Khem Raj]

On Mon, Aug 30, 2021 at 12:52 AM Robert P. J. Day <rpjday@crashcourse.ca> wrote:
>
>
>   i was going to extend section 3.3.17, "Using Virtual Providers",
> with an intro example using "udev" until i realized that that example
> doesn't use the "virtual/" notation. so ... why not? is there some
> distinction between other components that use the "virtual/" prefix,
> but a reason that one does not specify:
>
>   PROVIDES = "virtual/udev"
>
> rather than just:
>
>   PROVIDES = "udev"
>
> and then use the corresponding PREFERRED_PROVIDER_virtual/udev
> notation?

we also have VIRTUAL-RUNTIME_dev_manager which spans across systemd to mdev
so I guess we could but perhaps we already have this functionality
>
> rday
>
> 
>

Re: [OE-core] why "PREFERRED_PROVIDER_udev" and not "PREFERRED_PROVIDER_virtual/udev"?

[Robert P. J. Day]

On Mon, 30 Aug 2021, Khem Raj wrote:

> On Mon, Aug 30, 2021 at 12:52 AM Robert P. J. Day <rpjday@crashcourse.ca> wrote:
> >
> >
> >   i was going to extend section 3.3.17, "Using Virtual Providers",
> > with an intro example using "udev" until i realized that that example
> > doesn't use the "virtual/" notation. so ... why not? is there some
> > distinction between other components that use the "virtual/" prefix,
> > but a reason that one does not specify:
> >
> >   PROVIDES = "virtual/udev"
> >
> > rather than just:
> >
> >   PROVIDES = "udev"
> >
> > and then use the corresponding PREFERRED_PROVIDER_virtual/udev
> > notation?
>
> we also have VIRTUAL-RUNTIME_dev_manager which spans across systemd to mdev
> so I guess we could but perhaps we already have this functionality

  a followup, perhaps silly question -- is there anything special
about the "virtual/" prefix in the sense of being a provider? i mean,
other than being more aesthetically obvious?

rday

Re: [OE-core] why "PREFERRED_PROVIDER_udev" and not "PREFERRED_PROVIDER_virtual/udev"?

[Richard Purdie]

On Mon, 2021-08-30 at 03:52 -0400, Robert P. J. Day wrote:
>   i was going to extend section 3.3.17, "Using Virtual Providers",
> with an intro example using "udev" until i realized that that example
> doesn't use the "virtual/" notation. so ... why not? is there some
> distinction between other components that use the "virtual/" prefix,
> but a reason that one does not specify:
> 
>   PROVIDES = "virtual/udev"
> 
> rather than just:
> 
>   PROVIDES = "udev"
> 
> and then use the corresponding PREFERRED_PROVIDER_virtual/udev
> notation?

The "virtual/" namespace is just a way of namespacing some key dependencies
outside of the direct recipe namespace. 

virtual/libc is a better example and there are a few toolchain related ones.
There are several different libc implementations and virtual/libc just says you
want one without being specific.

Cheers,

Richard

Re: [OE-core] why "PREFERRED_PROVIDER_udev" and not "PREFERRED_PROVIDER_virtual/udev"?

[Richard Purdie]

On Tue, 2021-08-31 at 04:27 -0400, Robert P. J. Day wrote:
> On Mon, 30 Aug 2021, Khem Raj wrote:
> 
> > On Mon, Aug 30, 2021 at 12:52 AM Robert P. J. Day <rpjday@crashcourse.ca> wrote:
> > > 
> > > 
> > >   i was going to extend section 3.3.17, "Using Virtual Providers",
> > > with an intro example using "udev" until i realized that that example
> > > doesn't use the "virtual/" notation. so ... why not? is there some
> > > distinction between other components that use the "virtual/" prefix,
> > > but a reason that one does not specify:
> > > 
> > >   PROVIDES = "virtual/udev"
> > > 
> > > rather than just:
> > > 
> > >   PROVIDES = "udev"
> > > 
> > > and then use the corresponding PREFERRED_PROVIDER_virtual/udev
> > > notation?
> > 
> > we also have VIRTUAL-RUNTIME_dev_manager which spans across systemd to mdev
> > so I guess we could but perhaps we already have this functionality
> 
>   a followup, perhaps silly question -- is there anything special
> about the "virtual/" prefix in the sense of being a provider? i mean,
> other than being more aesthetically obvious?

Not really, it just signifies particular groups like the libc example I mention
in another mail.

Cheers,

Richard