netdev - Re: [net-next][PATCH 5/5] rds: rdma: update rdma transport for tos

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Date:   Tue, 5 Mar 2019 08:41:28 -0800
From:   Santosh Shilimkar <santosh.shilimkar@...cle.com>
To:     Gerd Rausch <gerd.rausch@...cle.com>, netdev@...r.kernel.org,
        davem@...emloft.net
Cc:     yanjun.zhu@...cle.com
Subject: Re: [net-next][PATCH 5/5] rds: rdma: update rdma transport for tos

On 3/5/2019 8:33 AM, Gerd Rausch wrote:
> Hi,
> 
> This patchset breaks compatibility...
> 
> On 04/02/2019 16.04, Santosh Shilimkar wrote:
>> --- a/net/rds/ib_cm.c
>> +++ b/net/rds/ib_cm.c
>> @@ -868,7 +870,7 @@ int rds_ib_cm_initiate_connect(struct rdma_cm_id *cm_id, bool isv6)
>>   
>>   	/* If the peer doesn't do protocol negotiation, we must
>>   	 * default to RDSv3.0 */
>> -	rds_ib_set_protocol(conn, RDS_PROTOCOL_VERSION);
>> +	rds_ib_set_protocol(conn, RDS_PROTOCOL_4_1);
>>   	ic->i_flowctl = rds_ib_sysctl_flow_control;	/* advertise flow control */
>>   
>>   	ret = rds_ib_setup_qp(conn);
> 
> The comment calls out to fallback to RDSv3.0, but the code assumes that v4.1 is
> the new common standard.
> 
> If there's a mechanism that ensures compatibility with older (pre-4.1) versions
> of RDS I am not seeing it.
Thats handled as part of the connection reject handler as part of 
negotiation.

> The inconsistency in comment vs. code doesn't help in that regard.
>
Yeah the comment should have been updated.

> And tests illustrated this incompatibility:
> 2 peers with this patchset can talk to eachother.
> Peers with a mix of post-this-patchset and pre-this-patchset can no longer talk
> to eachother.
> 
They can talk to each other as per Yanjun tests. He is working on 
setting it up net-next to see if something got missed out. Stay tune. 
Will update about the results.

Regards,
Santosh