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

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Date: Wed, 26 Jun 2024 18:29:02 +0000
From: Haiyang Zhang <haiyangz@...rosoft.com>
To: Konstantin Taranov <kotaranov@...rosoft.com>, Stephen Hemminger
	<stephen@...workplumber.org>, Leon Romanovsky <leon@...nel.org>
CC: 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



> -----Original Message-----
> From: Konstantin Taranov <kotaranov@...rosoft.com>
> Sent: Wednesday, June 26, 2024 2:20 PM
> To: Stephen Hemminger <stephen@...workplumber.org>; Leon Romanovsky
> <leon@...nel.org>; Haiyang Zhang <haiyangz@...rosoft.com>
> Cc: Konstantin Taranov <kotaranov@...ux.microsoft.com>; Wei Hu
> <weh@...rosoft.com>; sharmaajay@...rosoft.com; Long Li
> <longli@...rosoft.com>; jgg@...pe.ca; 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 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.
> > > > >
> > > > > 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.
> >
> > There is no documented semantics around any of the IF flags, only
> historical
> > precedent used by bond, team and bridge drivers. Initially Hyper-V VF
> used
> > bonding but it was impossibly difficult to make this work across all
> versions of
> > Linux, so transparent VF support was added instead. Ideally, the VF
> device
> > could be hidden from userspace but that required more kernel
> modifications
> > than would be accepted.
> 
> Thanks Stephen for the explanation!
> 
> I am also CCing Haiyang, who maintains Hyper-V netvsc.
> 

Yes, netvsc sets the IFF_SLAVE on VF for the bonding.

Acked-by: Haiyang Zhang <haiyangz@...rosoft.com>