Re: [PATCH v1] RDMA/core: Handle ARPHRD_NONE devices for iWARP

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Jun 09, 2023 at 04:49:49PM -0400, Tom Talpey wrote:
> On 6/7/2023 3:43 PM, Chuck Lever wrote:
> > From: Chuck Lever <chuck.lever@oracle.com>
> > 
> > We would like to enable the use of siw on top of a VPN that is
> > constructed and managed via a tun device. That hasn't worked up
> > until now because ARPHRD_NONE devices (such as tun devices) have
> > no GID for the RDMA/core to look up.
> > 
> > But it turns out that the egress device has already been picked for
> > us. addr_handler() just has to do the right thing with it.
> > 
> > Tested with siw and qedr, both initiator and target.
> > 
> > Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> > Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> > ---
> >   drivers/infiniband/core/cma.c |    3 +++
> >   1 file changed, 3 insertions(+)
> > 
> > This of course needs broader testing, but it seems to work, and it's
> > a little nicer than "if (dev_type == ARPHRD_NONE)".
> > 
> > One thing I discovered is that the NFS/RDMA server implementation
> > does not deal at all with more than one RDMA device on the system.
> > I will address that with an ib_client; SunRPC patches forthcoming.
> > 
> > diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
> > index 56e568fcd32b..c9a2bdb49e3c 100644
> > --- a/drivers/infiniband/core/cma.c
> > +++ b/drivers/infiniband/core/cma.c
> > @@ -694,6 +694,9 @@ cma_validate_port(struct ib_device *device, u32 port,
> >   	if (!rdma_dev_access_netns(device, id_priv->id.route.addr.dev_addr.net))
> >   		return ERR_PTR(-ENODEV);
> > +	if (rdma_protocol_iwarp(device, port))
> > +		return rdma_get_gid_attr(device, port, 0);
> 
> This might work, but I'm skeptical of the conditional. There's nothing
> special about iWARP that says a GID should come from the outgoing device
> mac. And, other protocols without IB GID addressing won't benefit.

The GID represents the source address, so it better come from the
outgoing device or something is really wrong.

iWARP gets a conditional because iwarp always has a single GID, other
devices do not work that way.

Jason