netdev - Re: [v3 PATCH 1/2] rhashtable: Add rhlist interface

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Date:   Mon, 19 Sep 2016 23:16:21 +0200
From:   Thomas Graf <tgraf@...g.ch>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Johannes Berg <johannes@...solutions.net>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org, tom@...bertland.com,
        Ben Greear <greearb@...delatech.com>
Subject: Re: [v3 PATCH 1/2] rhashtable: Add rhlist interface

On 09/19/16 at 07:00pm, Herbert Xu wrote:
> The insecure_elasticity setting is an ugly wart brought out by
> users who need to insert duplicate objects (that is, distinct
> objects with identical keys) into the same table.
> 
> In fact, those users have a much bigger problem.  Once those
> duplicate objects are inserted, they don't have an interface to
> find them (unless you count the walker interface which walks
> over the entire table).
> 
> Some users have resorted to doing a manual walk over the hash
> table which is of course broken because they don't handle the
> potential existence of multiple hash tables.  The result is that
> they will break sporadically when they encounter a hash table
> resize/rehash.
> 
> This patch provides a way out for those users, at the expense
> of an extra pointer per object.  Essentially each object is now
> a list of objects carrying the same key.  The hash table will
> only see the lists so nothing changes as far as rhashtable is
> concerned.
> 
> To use this new interface, you need to insert a struct rhlist_head
> into your objects instead of struct rhash_head.  While the hash
> table is unchanged, for type-safety you'll need to use struct
> rhltable instead of struct rhashtable.  All the existing interfaces
> have been duplicated for rhlist, including the hash table walker.
> 
> One missing feature is nulls marking because AFAIK the only potential
> user of it does not need duplicate objects.  Should anyone need
> this it shouldn't be too hard to add.
> 
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

Nice, I like how this simplifies users! Is this suitable for
ILA as well?

Acked-by: Thomas Graf <tgraf@...g.ch>