Re: [Ksummit-discuss] [CORE TOPIC] More useful types in the linux kernel

[Alexey Dobriyan <adobriyan@gmail.com>]

On Fri, Aug 12, 2016 at 12:07:11AM -0400, Matthew Wilcox wrote:
> On Aug 11, 2016 9:02 PM, "Josh Triplett" <josh@joshtriplett.org> wrote:
> > On Thu, Aug 11, 2016 at 11:51:52PM -0400, Matthew Wilcox wrote:
> > > Can we introduce types for this? We have a number of different return
> type
> > > conventions in the kernel:
> > >
> > > bool
> > > errno_t (-4095 to 0 are valid)
> > > count_t (-4095 to INT_MAX)
> > > long_count_t (-4095 to LONG_MAX)
> > > ulong_count_t (-4095 to -4096)
> > > struct foo _err*
> > >
> > > I think this is good programmer documentation in addition to being
> > > potentially useful to smatch.
> >
> > I'd love to see an explicit type distinct from "int" for "potentially an
> > errno".  And if any code uses "potentially an errno *or* a non-errno
> > non-zero return value", that should ideally use a distinct type as well.
> 
> I think the biggest problem is coming up with good names for the types. And
> the churn of introducing them, particularly converting function pointers
> and all occurrences.

Names are easy part (errno_t is perfect actually). The problem is that
once error is cleared, variable doesn't change to regular type anymore:

	errno_t rv;

	rv = f();
	if (rv < 0)
		return rv;
	int rv = rv;

which agains boils down to a language with real type system.