On Tue, Sep 20, 2016 at 02:42:58PM +0200, Peter Zijlstra wrote:
> On Tue, Sep 20, 2016 at 02:25:14PM +0200, Christoffer Dall wrote:
> > On Tue, Sep 20, 2016 at 11:42:23AM +0200, Peter Zijlstra wrote:
> > > On Mon, Sep 19, 2016 at 06:21:27PM +0100, Marc Zyngier wrote:
> > > > It is desirable to allow static keys to be integrated in structures,
> > > > as it can lead do slightly more readable code. But the current API
> > > > only provides DEFINE_STATIC_KEY_TRUE/FALSE, which is not exactly
> > > > nice and leads to the following idiom:
> > > >
> > > > static struct {
> > > > int foo;
> > > > struct static_key_false key;
> > > > } bar = {
> > > > .key = STATIC_KEY_FALSE_INIT,
> > > > };
> > > >
> > > > [...]
> > > >
> > > > if (static_branch_unlikely(&bar.key))
> > > > foo = -1;
> > > >
> > > > which doesn't follow the recommended API, and uses the internals
> > > > of the static key implementation.
> > > >
> > > > This patch introduces DECLARE_STATIC_KEY_TRUE/FALSE, as well as
> > > > INIT_STATIC_KEY_TRUE/FALSE, which abstract such construct and
> > > > allow the internals to evolve without having to fix everything else:
> > > >
> > > > static struct {
> > > > int foo;
> > > > DECLARE_STATIC_KEY_FALSE(key);
> > > > } bar = {
> > > > INIT_STATIC_KEY_FALSE(.key),
> > > > };
> > >
> > > Hurm..
> > >
> > > I think I like the first better, it looks more like actual C. Either way
> > > around you need to now manually match up the type and initializer.
> > >
> >
> > It may have been one of my review comments the prompted these patches,
> > because from reading Documentation/static-keys.txt, it seems that
> > referencing 'struct static_key' directly should be deprecated, and
> > instead developers should use the update API replacements.
>
> 'struct static_key' should indeed not be used and is deprecated. 'struct
> static_key_{true,false}' however should be fine.
ah, ok, didn't realize this, especially since static_key_false() is also
listed as deprecated ;)
>
> Part of the problem is naming, everything using 'struct static_key' has
> _insane_ names and the API is utterly confusing. The other part is that
> the new 2 type API simply has more functionality.
right, ok. As long as you're happy with slightly increased use of
directly embeddeing struct static_key_{true,false}, we're good.
Sorry for both if I encouraged confusion here.
Thanks,
-Christoffer
