netdev - Re: [RFC v3 3/6] can: make struct proto const

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Date:	Tue, 15 Mar 2011 22:28:13 +0100
From:	Oliver Hartkopp <socketcan@...tkopp.net>
To:	Kurt Van Dijck <kurt.van.dijck@....be>,
	Eric Dumazet <eric.dumazet@...il.com>
CC:	socketcan-core@...ts.berlios.de, netdev@...r.kernel.org
Subject: Re: [RFC v3 3/6] can: make struct proto const

On 14.03.2011 18:17, Kurt Van Dijck wrote:
> On Mon, Mar 14, 2011 at 05:42:23PM +0100, Eric Dumazet wrote:
>> Le lundi 14 mars 2011 à 16:02 +0100, Kurt Van Dijck a écrit :
>>
>>> I see your point.
>>> The reason I modified this was, as described, checkpatch.pl was complaining.
>>> Anyway, this sequence was protected by a spinlock 'proto_tab_lock'.
>>> I don't think it was a race.
>>>
>>> Did I miss something?
>>
>> As soon as proto_tab[proto] = cp; is done, another thread on another cpu
>> can read the pointer and follow it.
>>
>> Hmm, I missed can_create() also uses the spinlock protection, so you're
>> probably right.
>>
>> It seems a bit overkill :(
>> phonet uses RCU for example.

Hello Eric,

the RCU code in phonet is worth to consider. But loading and removing of
protocols is far away from being a hot path ... what would be the advantages
to move to RCU here?

> I'll keep that in mind.
> Switching CAN protos to RCU is far beyond to goal of this patch :-)

Anyway making the struct proto a const (and set the default defines in the CAN
protocols) is a nice cleanup. Let's wait for the feedback about the RCU from
Eric ... then this patch could be put into mainline independently from the
j1939 protocol.

Thanks,
Oliver
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