Re: [Ksummit-discuss] Should we force include <linux/err.h> when compiling all .c files?

[Hugh Dickins <hughd@google.com>]

On Tue, 29 Jul 2014, Luck, Tony wrote:

> > Perhaps, though see above about the handling of new source files.
> 
> Sounds like a job for checkpatch.pl to make sure that <linux/err.h>
> is included if a new file uses any of  'IS_ERR\|ERR_PTR\|PTR_ERR\|ERR_CAST'
> to help stop this spreading to new files.
> 
> It might be harder, but presumably still possible, to have it also check if
> any use of those macros is added to a file ... but it couldn't tell just by
> looking at the patch ... it would have to peek at the original file to see
> if there was already a #include <linux/err.h>
> 
> Without a check, or some regular scan, this problem is going to recur.

I keep wondering, what _is_ the problem being discussed here?

If someone uses IS_ERR etc without linux/err.h being included,
does the kernel behave in a dangerously unpredictable way?
Or does the build just fail?

So, there's a rule that everybody should include every header
file that's used directly by a particular source file.

Good rule, but somehow I doubt that omitting linux/err.h
is the sole example of that rule being broken.

And our response to that is to get the kbuild system to include
automatically any header files frequently forgotten?

Hugh