Messages in this thread | | | Date | Tue, 20 Sep 2016 14:42:58 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 1/2] jump_labels: Add API to deal with keys embedded in structures |
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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.
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.
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