netdev - Re: [Open-FCoE] [PATCH] fcoe: correct checking for bonding

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Date:	Tue, 01 Mar 2011 10:06:02 -0800
From:	Jay Vosburgh <fubar@...ibm.com>
To:	Joe Eykholt <joe.eykholt@...il.com>
cc:	Jiri Pirko <jpirko@...hat.com>,
	James.Bottomley@...senPartnership.com, netdev@...r.kernel.org,
	devel@...n-fcoe.org, linux-scsi@...r.kernel.org
Subject: Re: [Open-FCoE] [PATCH] fcoe: correct checking for bonding

Joe Eykholt <joe.eykholt@...il.com> wrote:

>On 2/28/11 10:37 PM, Jiri Pirko wrote:
>> Mon, Feb 28, 2011 at 06:54:29PM CET, joe.eykholt@...il.com wrote:
>>> On 2/28/11 9:15 AM, Jay Vosburgh wrote:
>>>> Jiri Pirko<jpirko@...hat.com>   wrote:
>>>>
>>>>> Check for IFF_BONDING as this flag is set-up for all bonding devices.
>>>>>
>>>>> Signed-off-by: Jiri Pirko<jpirko@...hat.com>
>>>>> ---
>>>>> drivers/scsi/fcoe/fcoe.c |    4 +---
>>>>> 1 files changed, 1 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/drivers/scsi/fcoe/fcoe.c b/drivers/scsi/fcoe/fcoe.c
>>>>> index 9f9600b..67714a4 100644
>>>>> --- a/drivers/scsi/fcoe/fcoe.c
>>>>> +++ b/drivers/scsi/fcoe/fcoe.c
>>>>> @@ -285,9 +285,7 @@ static int fcoe_interface_setup(struct fcoe_interface *fcoe,
>>>>> 	}
>>>>>
>>>>> 	/* Do not support for bonding device */
>>>>> -	if ((netdev->priv_flags&   IFF_MASTER_ALB) ||
>>>>> -	    (netdev->priv_flags&   IFF_SLAVE_INACTIVE) ||
>>>>> -	    (netdev->priv_flags&   IFF_MASTER_8023AD)) {
>>>>> +	if (netdev->priv_flags&   IFF_BONDING) {
>>>>> 		FCOE_NETDEV_DBG(netdev, "Bonded interfaces not supported\n");
>>>>> 		return -EOPNOTSUPP;
>>>>> 	}
>>>>
>>>> 	Based on past discussions, I believe the intent of the code is
>>>> to permit FCOE over bonding only for active-backup mode, and possibly
>>>> for -xor/-rr as well.
>>>>
>>>> 	I'm not sure if the slave or the master is what's being tested
>>>> here, so I'm not sure what the right thing to do is.  I suspect it's the
>>>> master, as I recall discussion of one configuration involving
>>>> active-backup mode balancing FCOE traffic over both the active and
>>>> inactive slaves.  FCOE uses the "orig_dev" logic in __netif_receive_skb
>>>> to have the packets delivered even on the nominally inactive slave.
>>>>
>>>> 	-J
>>>>
>>>> ---
>>>> 	-Jay Vosburgh, IBM Linux Technology Center, fubar@...ibm.com
>>>
>>> Right.  That was the intent.  It should work on the physical dev, but probably
>>> not on the master of the bond.
>>>
>>> If you have a master/slave bond for IPv4 between eth1 and eth2, say,
>>> and they are going to two different DCE (FCoE) switches, presumably on
>>> different VSANs but with ultimate access to the same disks,
>>> then you want to split the FCoE traffic in active/active
>>> mode using separate FCoE instances on eth1 and eth2 even though IP
>>> is using active/standby on bond0.  This should work.  But, putting fcoe
>>> on bond0 isn't going to do what you want.
>>>
>>> However, it seems like the check above shouldn't be checking
>>> IFF_SLAVE_INACTIVE.   I can't test this.
>>
>> OK. So I guess the right check should be for:
>> (netdev->priv_flags&  IFF_BONDING&&  netdev->flags&  IFF_MASTER)
>
>I think that's OK.  How about just checking for MASTER?
>When is MASTER going to be set without BONDING?

	One or two other things besides bonding use IFF_MASTER, but
IFF_BONDING is only for bonding.

>Otherwise I'd add some parens or I might code this as:
>
>	if ((netdev->priv_flags & (IFF_BONDING | IFF_MASTER)) ==
>	    (IFF_BONDING | IFF_MASTER))

	This doesn't work because the flags are kept in different
places, IFF_MASTER is in flags and IFF_BONDING in priv_flags.

	-J

>Which is less clear, I know, but used to generate better code.
>The compiler might generate the same code these days.
>Not that this is performance-critical or anything.
>
>> This would disable adding all bond devices (like bond0 etc) and allows
>> to use enslaved physdevs.
>>
>> Note that checking for mode is irrelevant here. Mode could be easily
>> changed later without fcoe knowing that.

	This is also true.

	-J

---
	-Jay Vosburgh, IBM Linux Technology Center, fubar@...ibm.com
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