[GitHub] [incubator-nuttx] patacongo edited a comment on issue #856: A error in include/errno.h?

[GitBox <gi...@apache.org>]

patacongo edited a comment on issue #856:
URL: https://github.com/apache/incubator-nuttx/issues/856#issuecomment-618799837


   > This logic seems to be wrong,(**&& !defined(**KERNEL****))seems redundant.
   > This error looks like copying a line of code, changing it, but forgetting to delete the extra parts.
   > To be honest, I often make this kind of mistakes.
   > 
   > #elif defined(CONFIG_BUILD_KERNEL) && !defined(**KERNEL**)
   
   No, it is not redundant `CONFIGI_BUILD_KERNEL` and `__KERNEL__` mean very different things.  The first is a build mode much like Linux where the kernel is built as a separately linked blob and applications a build as separately linked process blobs.
   
   `__KERNEL__` is an indication that we are currently compiling a portion of the kernel code.  `__KERNEL__` is valid is all build modes.
   
   So the too definitions are not related and it is correct to specify both.
   
   > ```
   > # if defined(**KERNEL**)
   > 
   > /* Kernel build. Kernel code has direct access */
   > # define __DIRECT_ERRNO_ACCESS 1
   > # else
   > 
   > /* User libraries for the kernel. Only indirect access from user
   > * libraries
   > */
   > # undef __DIRECT_ERRNO_ACCESS
   > # endif
   > 
   > #endif
   > ```
   
   This is also correct.  When we are build internal components of the OS then `__KERNEL__` will be defined and is is correct to access the `errno `variable in a different way by directly accessin OS internal data.
   
   Code that is not part of the internal OS components must use the indirect method by accessing the fake variable `errno`.  That is indirect in the since the `errno` is really a function call and may even translate to an OS system call in certain build modes.
   
   So it all looks correct to me and all makes good sense.
   
   
   


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