about virtual variable

[Adrian Ambrożewicz]

I feel rude for pointing out link to StackOverflow, but this guy really 
nailed it when it comes to easy explanation of 'virtual/' variable 
namespace :)

https://stackoverflow.com/a/37823742/8226884

W dniu 6/22/2020 o 14:48, zhouyuanqing8 at outlook.com pisze:
> Hi everyone,
> 
>       I would like to ask, is virtual a variable defined by bitbake? I 
> did not find it in the bitbake manual. What is the use of the virtual 
> variable? What would be the problem without this variable?
> 
> 
>     2.4. Preferences¶
>     <https://www.yoctoproject.org/docs/latest/bitbake-user-manual/bitbake-user-manual.html#bb-bitbake-preferences>
> 
> The|PROVIDES|list is only part of the solution for figuring out a 
> target's recipes. Because targets might have multiple providers, BitBake 
> needs to prioritize providers by determining provider preferences.
> 
> A common example in which a target has multiple providers is 
> "virtual/kernel", which is on the|PROVIDES|list for each kernel recipe. 
> Each machine often selects the best kernel provider by using a line 
> similar to the following in the machine configuration file:
> 
>       PREFERRED_PROVIDER_virtual/kernel = "linux-yocto"
> 
>