netdev - Re: [RFC 02/10] IB/hfi-vnic: Virtual Network Interface Controller (VNIC) Bus driver

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Message-ID: <20161121232629.GA67988@knc-06.sc.intel.com>
Date:   Mon, 21 Nov 2016 15:26:29 -0800
From:   "Vishwanathapura, Niranjana" <niranjana.vishwanathapura@...el.com>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     Doug Ledford <dledford@...hat.com>, linux-rdma@...r.kernel.org,
        netdev@...r.kernel.org,
        Dennis Dalessandro <dennis.dalessandro@...el.com>
Subject: Re: [RFC 02/10] IB/hfi-vnic: Virtual Network Interface Controller
 (VNIC) Bus driver

On Mon, Nov 21, 2016 at 02:39:30PM -0700, Jason Gunthorpe wrote:
>On Mon, Nov 21, 2016 at 01:30:17PM -0800, Vishwanathapura, Niranjana wrote:
>> On Sat, Nov 19, 2016 at 12:04:45PM -0700, Jason Gunthorpe wrote:
>> >On Fri, Nov 18, 2016 at 02:42:10PM -0800, Vishwanathapura, Niranjana wrote:
>> >>+HFI-VNIC DRIVER
>> >>+M:	Dennis Dalessandro <dennis.dalessandro@...el.com>
>> >>+M:	Niranjana Vishwanathapura <niranjana.vishwanathapura@...el.com>
>> >>+L:	linux-rdma@...r.kernel.org
>> >>+S:	Supported
>> >>+F:	drivers/infiniband/sw/intel/vnic
>> >
>> >This is either a net driver or a ULP, no idea why it should go in this
>> >directory!?
>> >
>> >It sounds like an ethernet driver, so you should probably put it
>> >there...
>> >
>>
>> The hfi_vnic is an Ethernet driver. It is similar to ULP like ipoib, but
>> instead it is Ethernet over Omni-path here.
>> The VNIC Ethernet (hfi_vnic) driver encapsulates Ethernet packets in an
>> Omni-path header.
>> The hfi_vnic Ethernet driver do not access the HW. It interfaces with HFI1
>> driver which sends/receives Omni-Path encapsulated Ethernet frames from HW.
>> Also, the VNIC control path driver (VEMA) is an IB MAD agent which should be
>> under drivers/infiniband/.. .
>> Putting the VNIC Ethernet driver and the VNIC control driver together under
>> a single module (hfi_vnic.ko) provided a simpler interface between them.
>>
>> So, we have put the driver under drivers/infiniband/sw/intel for two reasons:
>> a) We have VNIC control driver (VEMA) which is an IB mad agent.
>> b) hfi_vnic Ethernet driver is dependent on HFI1 driver for sending/receving
>> Omni-path encapsulated Ethernet packets from HW.
>
>Sounds like this driver belongs under net/ someplace to me.
>
>NAK on drivers/infiniband/sw/ at least - that dir is only for HCA
>drivers.
>

I did not see any example IB mad agent outside drivers/inifiniband folder.
I did see some netdev drivers outside the net/ folder (like ipoib and 
drivers/infiniband/hw/nes/).
The hfi_vnic Ethernet driver is entirely a soft driver without any HW access.
Also, any interface changes between hfi_vnic and the HFI driver makes it 
difficult to manage if they are under two subsystems/maintainers.
So drivers/infiniband is probably more approriate for this driver.

We have 'rdmavt' and 'soft-roce' drivers under drivers/infiniband/sw/ folder 
which are soft drivers similar to hfi_vnic. So we decided to put 'hif_vnic' 
under there.
Other places under drivers/infiniband where we can put this driver are,
drivers/infiniband/ulp/hfi_vnic
drivers/infiniband/hw/hfi_vnic

>> >>+/* hfi_vnic_bus_init - initialize the hfi vnic bus drvier */
>> >>+static int hfi_vnic_bus_init(void)
>> >>+{
>> >>+	int rc;
>> >>+
>> >>+	ida_init(&hfi_vnic_ctrl_ida);
>> >>+	idr_init(&hfi_vnic_idr);
>> >>+
>> >>+	rc = bus_register(&hfi_vnic_bus);
>> >
>> >Why on earth do we need this? Didn't I give you enough grief for the
>> >psm stuff and now you want to create an entire subystem hidden away!?
>> >
>> >Use some netlink scheme to control your vnic like the rest of the net
>> >stack..
>> >
>>
>> The hfi_vnic_bus is only abstracting the HW independent functionality (like
>> Ethernet interface, encapsulation, IB MAD interface etc) with the HW
>> dependent functionality (sending/receiving packets on the wire).
>> Thus providing a cleaner interface between HW independent hfi_vnic Ethernet
>> and Control drivers and the HW dependent HFI1 driver.
>
>That doesn't explain anything, sound like you don't need it so get rid
>of it.
>
>> There is no other User interface here other than the standard Ethernet
>> interface through network stack.
>
>Good, then this isn't needed, because it doesn't provide a user interface.
>

Can you explain what exactly you are asking to get rid of here and why?

>> #ls /sys/bus/hfi_vnic_bus/devices/
>>    hfi_vnic_ctrl_00         /* control device for HFI instance 0 */
>>    hfi_vnic_00.01.00        /* first VNIC port on HFI instance 0, port 1 */
>
>Jason