Re: [PATCH 10/18] rhashtable: remove rhashtable_walk_peek()

From: NeilBrown <neilb@suse.com>
To: Tom Herbert <tom@herbertland.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
	Thomas Graf <tgraf@suug.ch>,
	Linux Kernel Network Developers <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Tom Herbert <tom@quantonium.net>
Subject: Re: [PATCH 10/18] rhashtable: remove rhashtable_walk_peek()
Date: Wed, 06 Jun 2018 15:07:57 +1000	[thread overview]
Message-ID: <87in6wo636.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <CALx6S36Ce-rXQMzmFYZVPGD10Bo6udvRAHiZ5gWwnzVwoTVv0w@mail.gmail.com>

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On Tue, Jun 05 2018, Tom Herbert wrote:

> On Mon, Jun 4, 2018 at 6:00 PM, NeilBrown <neilb@suse.com> wrote:
>
>> On Mon, Jun 04 2018, Tom Herbert wrote:
>>
>> >>
>> >> Maybe a useful way forward would be for you to write documentation for
>> >> the rhashtable_walk_peek() interface which correctly describes what it
>> >> does and how it is used.  Given that, I can implement that interface
>> >> with the stability improvements that I'm working on.
>> >>
>> >
>> > Here's how it's documented currently:
>> >
>> > "rhashtable_walk_peek - Return the next object but don't advance the
>> iterator"
>> >
>> > I don't see what is incorrect about that.
>>
>> rhashtable_walk_next is documented:
>>
>>  * rhashtable_walk_next - Return the next object and advance the iterator
>>
>> So it seems reasonable to assume that you get the same object, no matter
>> which one you call.  Yet this is not (necessarily) the case.
>>
>>
>> >                                           Peek returns the next object
>> > in the walk, however does not move the iterator past that object, so
>> > sucessive calls to peek return the same object. In other words it's a
>> > way to inspect the next object but not "consume" it. This is what is
>> > needed when netlink returns in the middle of a walk. The last object
>> > retrieved from the table may not have been processed completely, so it
>> > needs to be the first one processed on the next invocation to netlink.
>>
>> I completely agree with this last sentence.
>> We typically need to process the last object retrieved.  This could also
>> be described as the previously retrieved object.
>> So rhashtable_walk_last() and rhashtable_walk_prev() might both be
>> suitable names, though each is open to misinterpretation.
>>
>
> rhashtable_walk_last is better, but still could have the connotation that
> it returns the last element in the list or table. How about
> rhashtable_walk_last_seen or rhashtable_walk_last_iter?

I'd be quite happy with rhashtable_walk_last_seen().
I also be happy to keep rhasthable_walk_peek() but to implement it
as
  rhashtable_walk_last_seen() ?: rhashtable_walk_next()

I'll send patches to that effect some time this week.

Thanks,
NeilBrown

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