Bug 10011

Summary:	Suggested addition to the PROVIDES glossary entry to explain virtual targets
Product:	[Documentation] Reference	Reporter:	ulfalizer
Component:	handbook	Assignee:	Scott Rifenbark <srifenbark>
Status:	RESOLVED FIXED	QA Contact:
Severity:	normal
Priority:	Medium	CC:	bluelightning, poky.doc.watcher, poky.watcher, sgw, srifenbark
Version:	2.2
Target Milestone:	2.2 M4
Hardware:	x86
OS:	Multiple
Whiteboard:
OS type for building Yocto:	---	Type of Regression:	---
Verified:		Documentation change:	Done (doc changes complete)

Description ulfalizer 2016-07-23 11:47:12 UTC

There doesn't seem to be much documentation on virtual targets at the moment. I suggest adding the following to the end of the PROVIDES glossary entry in the Yocto Reference Manual and BitBake manual:

  In addition to providing recipes under alternate names, the PROVIDES
  mechanism is also used to implement <i>virtual targets</i>. A virtual target
  is a name that corresponds to some particular functionality, e.g. a Linux
  kernel. Recipes that provide the functionality in question list the virtual
  target in PROVIDES. Recipes that depend on the functionality in question can
  include the virtual target in DEPENDS to leave the choice of provider open.
  
  Conventionally, virtual targets have names on the form "virtual/function"
  (e.g. "virtual/kernel"). The slash is simply part of the name and has no
  syntactic significance.
  
  The [PREFERRED_PROVIDER] variable is used to select which particular recipe
  provides a virtual target.

Cheers,
Ulf

Comment 1 ulfalizer 2016-07-23 11:50:36 UTC

In the PREFERRED_PROVIDER glossary entry, the word "provide" in the opening sentence could be turned into a link as well:

  If multiple recipes [provide](http://www.yoctoproject.org/docs/2.2/ref-manual/ref-manual.html#var-PROVIDES) an item...

Comment 2 Scott Rifenbark 2016-07-29 17:14:59 UTC

Hi Ulf, 

See http://www.yoctoproject.org/docs/2.2/ref-manual/ref-manual.html#var-PROVIDES for the changes in the ref-manual.  When we settle on these, I will update the same variable in the BitBake User Manual.  I am going to wait though until we are good here.  

Regarding linking the normal work "provides", I don't want to do that as I have not done that in the past.

Scott

Comment 3 ulfalizer 2016-07-29 18:53:53 UTC

Looks good to me.

Thanks,
Ulf

Comment 4 Scott Rifenbark 2016-07-29 21:10:01 UTC

Thanks Ulf, 

I am closing the bug.  Here is the link to the changed version in the BitBake manual now - http://www.yoctoproject.org/docs/2.2/bitbake-user-manual/bitbake-user-manual.html#var-PROVIDES.

Scott