[PATCH 0/6] drm: Introduce consistent reference counting APIs

[Thierry Reding]

On Thu, Feb 09, 2017 at 08:07:41PM +0100, Daniel Vetter wrote:
> On Thu, Feb 09, 2017 at 07:39:33PM +0200, Jani Nikula wrote:
> > On Thu, 09 Feb 2017, Daniel Vetter <daniel at ffwll.ch> wrote:
> > > On Thu, Feb 09, 2017 at 04:10:12PM +0200, Jani Nikula wrote:
> > >> On Wed, 08 Feb 2017, Thierry Reding <thierry.reding at gmail.com> wrote:
> > >> > This series introduces DRM reference counting APIs that are consistent
> > >> > with other reference counting APIs in the kernel. They are also much
> > >> > shorter. Compatibility aliases are added to keep existing code working
> > >> > and will stay in place until all users of the old APIs are gone.
> > >> 
> > >> I like it.
> > >> 
> > >> But it makes drm_connector_list_iter_{get,put} stick out like a sore
> > >> thumb. Something for the TODO list I guess.
> > >
> > > Hm, why is that one the sore thumb now? Just because it's really long? It
> > > does acquire/drop references behind the scenes, that's why I went with the
> > > _get/put postfixes ...
> > 
> > I think the assumption is that get/put work on an object, and you can
> > get/put as many times as you like, as long as you keep them at
> > balance. AFAICT this doesn't hold for iter.
> 
> Hm right. What else should we use instead? start/stop are confusing in the
> context of list walking, create/destroy maybe?

I rather like the _begin()/_end() suffix that I think iterators have in
the C++ STL. Well, I guess it's really .end() and .begin() methods in
C++.

But the following reads rather nicely:

	drm_connector_list_iter_begin(dev, &iter);

	drm_for_each_connector_iter(connector, &iter)
		...

	drm_connector_list_iter_end(&iter);

Alternatively some other iterators simply use an _init() suffix to
initialize the iterator. The kernel has a few of these, such as the
of_phandle_iterator (see include/linux/of.h) or of_pci_range_parser (see
include include/linux/of_address.h).

EFI code uses _begin()/_end() in include/linux/efi.h, cgroups seems to
have _start()/_end() in include/linux/cgroup.h. include/linux/klist.h
uses klist_iter_init()/klist_iter_exit(). include/linux/rhashtable.h has
rhashtable_walk_start()/rhashtable_walk_stop().

A quick grep also shows other variants, one of them being _first(), but
those don't have an explicit end function.

So there's quite a few options to choose from, but I guess that doesn't
make it any easier.

If this was a poll, my vote would go to _begin()/_end().

Thierry
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