netdev - Re: [PATCH rdma-next 1/1] RDMA/mana_ib: Set correct device into ib

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Date: Wed, 26 Jun 2024 18:33:54 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Stephen Hemminger <stephen@...workplumber.org>
Cc: Konstantin Taranov <kotaranov@...rosoft.com>,
	Konstantin Taranov <kotaranov@...ux.microsoft.com>,
	Wei Hu <weh@...rosoft.com>,
	"sharmaajay@...rosoft.com" <sharmaajay@...rosoft.com>,
	Long Li <longli@...rosoft.com>, "jgg@...pe.ca" <jgg@...pe.ca>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	linux-netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH rdma-next 1/1] RDMA/mana_ib: Set correct device into ib

On Wed, Jun 26, 2024 at 08:27:31AM -0700, Stephen Hemminger wrote:
> On Wed, 26 Jun 2024 15:11:18 +0300
> Leon Romanovsky <leon@...nel.org> wrote:
> 
> > On Wed, Jun 26, 2024 at 09:05:05AM +0000, Konstantin Taranov wrote:
> > > > > When mc->ports[0] is not slave, use it in the set_netdev.
> > > > > When mana is used in netvsc, the stored net devices in mana are slaves
> > > > > and GIDs should be taken from their master devices.
> > > > > In the baremetal case, the mc->ports devices will not be slaves.  
> > > > 
> > > > I wonder, why do you have "... | IFF_SLAVE" in __netvsc_vf_setup() in a first
> > > > place? Isn't IFF_SLAVE is supposed to be set by bond driver?
> > > >   
> > > 
> > > I guess it is just a valid use of the IFF_SLAVE bit. In the bond case it is also set
> > > as a BOND netdev. The IFF_SLAVE helps to show users that another master
> > > netdev should be used for networking. But I am not an expert in netvsc.  
> > 
> > The thing is that netvsc is virtual device like many others, but it is
> > the only one who uses IFF_SLAVE bit. The comment around that bit says
> > "slave of a load balancer.", which is not the case according to the
> > Hyper-V documentation.
> > https://learn.microsoft.com/en-us/windows-hardware/drivers/network/overview-of-hyper-v
> > 
> > You will need to get Ack from netdev maintainers to rely on IFF_SLAVE
> > bit in the way you are relying on it now.
> 
> This is used to tell userspace tools to not interact directly with the device.
> For example, it is used when VF is connected to netvsc device.
> It prevents things like IPv6 local address, and Network Manager won't modify device.

You described how hyper-v uses it, but I'm interested to get acknowledgment
that it is a valid use case for IFF_SLAVE, despite sentence written in the comment.

Thanks