Re: [PATCH RFC] RDMA/core: Handle ARPHRD_NONE devices

[Chuck Lever III <chuck.lever@oracle.com>]

> On Jun 2, 2023, at 6:18 PM, Tom Talpey <tom@talpey.com> wrote:
> 
> On 6/2/2023 3:24 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.
>> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
>> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
>> ---
>>  drivers/infiniband/core/cma.c |    4 ++++
>>  1 file changed, 4 insertions(+)
>> diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
>> index 56e568fcd32b..3351dc5afa17 100644
>> --- a/drivers/infiniband/core/cma.c
>> +++ b/drivers/infiniband/core/cma.c
>> @@ -704,11 +704,15 @@ cma_validate_port(struct ib_device *device, u32 port,
>>   ndev = dev_get_by_index(dev_addr->net, bound_if_index);
>>   if (!ndev)
>>   return ERR_PTR(-ENODEV);
>> + } else if (dev_type == ARPHRD_NONE) {
>> + sgid_attr = rdma_get_gid_attr(device, port, 0);
>> + goto out;
>>   } else {
>>   gid_type = IB_GID_TYPE_IB;
>>   }
>>     sgid_attr = rdma_find_gid_by_port(device, gid, gid_type, port, ndev);
>> +out:
>>   dev_put(ndev);
>>   return sgid_attr;
>>  }
> 
> I like it, but doesn't this test in siw_main.c also need to change?
> 
> static struct siw_device *siw_device_create(struct net_device *netdev)
> {
> ...
> --> if (netdev->type != ARPHRD_LOOPBACK && netdev->type != ARPHRD_NONE) {
> addrconf_addr_eui48((unsigned char *)&base_dev->node_guid,
>    netdev->dev_addr);
> } else {
> /*
> * This device does not have a HW address,
> * but connection mangagement lib expects gid != 0
> */
> size_t len = min_t(size_t, strlen(base_dev->name), 6);
> char addr[6] = { };
> 
> memcpy(addr, base_dev->name, len);
> addrconf_addr_eui48((unsigned char *)&base_dev->node_guid,
>    addr);
> }

I'm not sure that code does anything. The base_dev's name field
is actually not initialized at that point, so nothing is copied
here.

If you're asking whether siw needs to build a non-zero GID to
make the posted patch work, more testing is needed; but I don't
believe the GID has any relevance -- the egress ib_device is
selected based entirely on the source IP address in this case.


--
Chuck Lever