netdev - Re: [PATCH net-next v2 5/6] bonding: restructure and add rcu for bond_for_each_slave

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Date:	Wed, 04 Sep 2013 23:02:28 +0800
From:	Ding Tianhong <dthxman@...il.com>
To:	Veaceslav Falico <vfalico@...hat.com>
CC:	Ding Tianhong <dingtianhong@...wei.com>,
	Jay Vosburgh <fubar@...ibm.com>,
	Andy Gospodarek <andy@...yhouse.net>,
	"David S. Miller" <davem@...emloft.net>,
	Nikolay Aleksandrov <nikolay@...hat.com>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 5/6] bonding: restructure and add rcu for
 bond_for_each_slave_next()

于 2013/9/4 18:35, Veaceslav Falico 写道:
> On Wed, Sep 04, 2013 at 05:44:15PM +0800, Ding Tianhong wrote:
> ...snip...
>> +/* Check whether the slave is the only one in bond */
>> +#define bond_is_only_slave(bond, pos) \
>> + (((pos)->list.prev == &(bond)->slave_list) && \
>> + ((pos)->list.next == &(bond)->slave_list))
>
> Could be done without pos at all -
>
> !list_empty(&(bond)->slave_list) && \
> &(bond)->slave_list.next == &(bond)->slave_list.prev
>
> If we have only one slave and pos is NOT our slave then... well.. we have
> big troubles.
>
yes, more simple more beautiful, thanks.

but if the pos is not our slave, it is the mistake, not bug. :)

>> +
>> /**
>> * bond_for_each_slave_from - iterate the slaves list from a starting 
>> point
>> * @bond: the bond holding this list.
>> * @pos: current slave.
>> - * @cnt: counter for max number of moves
>> * @start: starting point.
>> *
>> * Caller must hold bond->lock
>> */
>> -#define bond_for_each_slave_from(bond, pos, cnt, start) \
>> - for (cnt = 0, pos = start; pos && cnt < (bond)->slave_cnt; \
>> - cnt++, pos = bond_next_slave(bond, pos))
>> +#define bond_for_each_slave_from(bond, pos, start) \
>> + for (pos = start; pos && (bond_is_only_slave(bond, start) ? \
>> + &pos->list != &bond->slave_list : \
>> + &pos->list != &start->list); bond_is_only_slave(bond, start) ? \
>> + (pos = list_entry(pos->list.next, typeof(*pos), list)) : \
>> + (pos = bond_next_slave(bond, pos)))
>
> Did you check that?
>
> pos = slave1 (bond has more than one slave);
> pos && &pos->list != &slave1->list - false.
>
> We won't ever enter this loop if we have >1 slaves.
>
> I don't understand this at all.
>

ok, the logic is : if slaves == 1, run once for the slave.
if slaves > 1, run loops until reach the end list.
I could not get a better way to simplify the function, I think it is a 
suitable scheme.

by the way, I test the function and works well. :)

>> +
>> +/**
>> + * bond_for_each_slave_from_rcu - iterate the slaves list from a 
>> starting point
>> + * @bond: the bond holding this list.
>> + * @pos: current slave.
>> + * @start: starting point.
>> + *
>> + * Caller must hold rcu_read_lock
>> + */
>> +#define bond_for_each_slave_from_rcu(bond, pos, start) \
>> + for (pos = start; pos && (bond_is_only_slave(bond, start) ? \
>> + &pos->list != &bond->slave_list : \
>> + &pos->list != &start->list); bond_is_only_slave(bond, start) ? \
>> + (pos = list_entry_rcu(pos->list.next, typeof(*pos), list)) : \
>> + (pos = bond_next_slave_rcu(bond, pos)))
>
> Ditto as bond_for_each_slave_from() and, also, see my comment about RCU
> from patch 1.
>
>>
>> /**
>> * bond_for_each_slave - iterate over all slaves
>> -- 
>> 1.8.2.1
>>
>>
>>
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